"Controls on information are growing significantly, and official efforts to exploit personal data are also on the rise," said Steven Aftergood, director of the Project on Government Secrecy at the Federation of American Scientists, or FAS.

The change has been dramatic. In the 1997 fiscal year, the federal government spent $3.4 billion on securing classified information, a figure that rose to $7.7 billion for 2005. Similarly, the government declassified 204 million pages of documents in 1997 but a mere 29.6 million in 2005. (Those numbers come from calculations by OpenTheGovernment.org, an umbrella group that includes FAS, the Reporters Committee for Freedom of the Press, the Electronic Frontier Foundation, and the Society of Professional Journalists.)

At the same time, surveillance of Americans by the federal government has steadily increased. President Bush has acknowledged bypassing the checks and balances of the courts when enlisting the National Security Agency in an extensive surveillance program. Congress is discussing whether to rewrite that law.

A lawsuit pending in San Francisco has yielded allegations of far more extensive NSA surveillance. Former AT&T employee Mark Klein released documents alleging the company spliced its fiber optic cables and ran a duplicate set for the NSA to Room 641A at its 611 Folsom St. building in San Francisco. Redacted documents show that AT&T has tried to offer benign reasons for the existence of such a room. (AT&T refuses to comment.)

Listening in

The Bush administration has been especially secretive about the extent of the NSA program and how it works. But even the far smaller number of known wiretaps performed under court order has grown since 2001, government statistics show. Not only has eavesdropping on criminal activities increased, but Internet and telephone wiretaps performed under the Foreign Intelligence Surveillance Act have roughly doubled from 2001 to 2005.

That has happened as executive branch agencies have become far more resistant to Freedom of Information Act requests. "The very fabric of our democracy is undergoing a kind of a mutation, in which access to information is no longer a given," said FAS's Aftergood. "It's something that you increasingly have to struggle for or make a conscious effort to obtain."

In addition, new justifications for not releasing unclassified government documents to the public are proliferating. In the last few years, especially, terms like "For Official Use Only," "Controlled But Unclassified," "DEA Sensitive," "Confidential Business Information" have appeared on more and more documents--even though, in almost all cases, there's no legal justification for them.

"Such unchecked secrecy threatens accountability in governments and promotes conflicts of interest by allowing those with an interest in disclosure or concealment to decide between openness or secrecy," a recent report by OpenTheGovernment.org states.

In addition, some expansions of government secrecy--perhaps including NORAD's deletion of the transcript--appear to be driven by fear of public criticism. In 2003, the U.S. Army surreptitiously pulled the plug on one of its more popular Web sites after a report embarrassing to the military appeared on it. In another example, the names of the members of the Defense Science Board--an obscure but influential advisory body that influences military policy and had a budget of $3.6 million a year--have vanished from the group's public Web site.

That also happened in 2002 when the Defense Department tried to quell public concern about the now-defunct Total Information Awareness project by deleting files from the Web.

First, biographical information about TIA project leaders, including retired Adm. John Poindexter, disappeared. Then the TIA site shrank even more, with the slogan and logo for the TIA project--a Masonic pyramid that eyeballs the globe--vanishing, a highly unusual move for any government agency. Finally, a few weeks later, a diagram that explained the TIA project was erased.

For their part, the Bush administration and its allies argue that critics are blind to the fact that the United States is embroiled in a war on terror that could last for many more years.

Critics of such programs "seem surprised that we wouldn't tell the targets, that we would keep surveillance secret," said Todd Gaziano, director of the Center for Legal and Judicial Studies at the Heritage Foundation, a conservative Washington, D.C., think tank, referring to the NSA program. "It would be kind of laughable in any other era, and I don't know why it's not laughable now."

Gaziano, who likened the Sept. 11 attacks to those on Pearl Harbor, said he found it "absurd" that anyone would argue surveillance and secrecy have been hallmarks of the Bush administration. Anyone who's read up on American history should know that Woodrow Wilson and Franklin Delano Roosevelt conducted far more sweeping interceptions during World Wars I and II, he said.

"My theory is that we are not doing enough surveillance," Gaziano said.

"If Osama bin Laden calls up the next Mohammad Atta and says, 'Start Operation Anthrax.' And then Mohammad Atta starts calling around to a company inquiring about helicopter rides or about machinery that's useful in milling anthrax, it doesn't matter whether the caller on the other side is a legitimate, innocent American," he added. "We ought to know every plan."

Heather Mac Donald, a senior fellow at the conservative-oriented Manhattan Institute for Policy Research, said she's unconvinced that any "significant incursions" on civil liberties have occurred since Sept. 11. "This has been one of the most law-abiding wars, overseen by lawyers at every step," she said.

The Patriot Act's expansion of government powers, for instance, is "shot through with checks and balances," she said. "There's hardly a power in it that doesn't require some sort of judicial oversight. The government simply doesn't have the resources available to be engaged in completely groundless fishing expeditions or spying for the sake of spying."

And allegations of heightened government secrecy are just "preposterous," she added. Take, for instance, a Patriot Act provision that allows delayed search warrants, permitting police to secretly enter a home and notify the targeted person after the fact. "People thought that was improper, that there should be full sunshine disclosure of terrorism investigations," Mac Donald said. "Well, that's absolutely absurd."

Mac Donald acknowledged that she hadn't been persuaded by the Bush administration's assertions that it had the power to ignore the Foreign Intelligence Surveillance Act when authorizing the NSA to engage in widespread surveillance of communications involving suspected terrorists. But that's no reason to shut down the program, she said. The administration could have resolved those concerns by simply asking for changes to FISA, whose requirements of probable cause don't make sense "when you're initially looking at computers working with large amounts of data."

"I think the NSA program is a good program and an essential program," she added. "I don't think it has been used abusively to violate anybody's privacy."

The level of surveillance conducted by the United States also pales in comparison with other countries, particularly in Europe, said Gary Schmitt, a resident scholar at the conservative-leaning American Enterprise Institute.

"Even though we're far less intrusive than many people would suspect, the intrusive capabilities we have are probably about right given the threat that we face," Schmitt said. "I think we've probably got pretty much the right balance."

In a new age of rapid and widespread ID checks, locked and bulletproof cockpit doors in airliners, armed pilots, tracking foreigners' visas and monitoring Muslim and Arab communities, few expect a precise repeat of the plot that used airline hijackings to bring down big buildings.

The unsettling reality of terrorism, however, is that it is always in search of new ways to accomplish mass death and destruction. And always in search of the weakest link.

Authorities have disrupted a number of high-profile plots, including last month's bombing scare on as many as 10 Britain-to-U.S. flights. The CIA has helped ensnare some 5,000 terror suspects around the world.

And the government has imposed hundreds of security measures on foreign visitors and U.S. residents alike, from making travelers take off their shoes at airport checkpoints to eavesdropping on phone and e-mail conversations.

But glaring gaps in the security net remain.

Undercover inspectors testing the nation's security system have repeatedly sneaked weapons through airport checkpoints, entered the country with fake identification and foiled detectors that catch the trace amounts of radiation in kitty litter and bananas, but not always nuclear materials. Air testers to sniff out biological agents are becoming obsolete. And not all port or airline cargo is rigorously inspected.

And, as Hurricane Katrina showed last year, disaster response systems at all levels of government are woefully unprepared for a catastrophe.

"No matter what you do, it's not enough," said Rep. Carolyn Maloney, D-N.Y., co-chair of a congressional 9/11 caucus. "But the systems we've worked hard on to put in place are not working."

Homeland Security Secretary Michael Chertoff, whose department was created in 2003 as a result of 9/11, points to strides made in sharing intelligence and screening passengers and cargo on flights and at seaports as proof that the country has been made safer without shutting down commerce. Yet he acknowledges more needs to be done in his agency that largely grapples with reacting to past crises while also thinking about what terrorists might try next.

The intelligence community spends a significant amount of time doing what Chertoff described as "putting ourselves in the heads of terrorists - looking at emerging techniques and trying to figure out how terrorists might exploit our systems."

In one example, Chertoff said, the department last year relaxed its ban on scissors and small innocuous tools from being carried on planes to give inspectors more time to look for explosive devices. Screeners also are now being trained to interpret facial expressions and other behavioral patterns to pick out suspicious travelers.

"We will live with some form of this problem for a very long time," Chertoff said in an hour-long interview last month wedged between a phone call with British Home Secretary John Reid about the foiled flight plot and a meeting with FEMA director David Paulison about the hurricane season.

Several government-appointed panels - including the 9/11 Commission - have concluded over the last five years that the nation was vastly unprepared for the deadly attacks.

Their findings triggered a massive reshuffling of the government's counterterror missions, the largest since the Defense Department was created in 1947. In addition to merging 22 agencies into the new Homeland Security Department, a new position of intelligence director to oversee the nation's 16 spy agencies was established.

Congress approved policies such as the USA Patriot Act, allowing more surveillance in counterterrorism investigations. Federal spending on domestic security programs has more than tripled since 2001, to $55 billion this year, almost equal to what is spent on education.

The results have been mixed. Criticism for Homeland Security has run from sweeping (for cutting emergency responder funding to New York and Washington) to nitpicky (the color-coded threat alert system is too vague to be meaningful).

"Everything the department was supposed to do is still, at best, a work in progress," said Clark Kent Evin, Homeland Security's former inspector general.

Meanwhile, the government's once-greatest target in the war on terror - Osama bin Laden - remains on the loose. Michael Scheuer, the former head of the now-defunct CIA unit dedicating to finding the al-Qaida leader, said catching him now is mostly a matter of luck. "He's going to have to zig when we zag and we'll end up in the same place at once," Scheuer said.

With or without bin Laden, authorities expect al-Qaida's threat won't dim in coming years.

Some sympathizers - including small pockets of homegrown Islamic extremists already in the United States - may not even be directly linked to al-Qaida but aim to carry out its mission. Those who make up al-Qaida's core will wait years, and even decades, for the chance to attack when America least expects it.

"I'm convinced they're prepared to wait centuries if they have to," former Homeland Security Secretary Tom Ridge said. "They're looking much longer term than we are. So we have to match their patience with our persistence and our continued focus. We can never let our guard down."

"I believe we have done well in some tactical areas, but we are slipping strategically. That is to say, our actions over the long term are making the terror threat much worse," said Daniel Benjamin, a senior fellow with the Washington-based think tank, the Center for Strategic & International Studies (CSIS).

"Although we have made some tactical strides in terms of dismantling al-Qaida, the threat has spread to many different regions," he said.

Benjamin said he "absolutely" didn't believe that Iraq was the right place to fight terrorism.

"I consider now as I did at the time that the invasion of Iraq is a huge mistake," he added.

The United States is not going to win the war on terror very soon because "the consequences of going into Iraq are going to be with us for a while and has set us back considerably," he added.

The way the United States will win over the terror threat is "by convincing the Muslim world that there is a viable way to be modernized and that part of the world has an interest in being allied with the West," he said. "But we are not doing that."

"I think the struggle against terrorism is going to be quite long. And the question really is, how long it will be before we start to go into the right direction?" said Benjamin, who served the National Security Council in the Clinton administration from 1994 to 1999.

If Democrats take over the Congress in November, that may bring changes to Iraq, but that "is not going to make the jihadist threat go away," he said.

On the possibility of another 9/11-like attack, Benjamin said, "I think at the moment that the ability of those who are most skilled to carry out catastrophic attacks has been limited, so we are more likely to see attacks on the scale of Madrid in places like Europe or the Mideast."

"But I don't think you can really rule out a catastrophic attack because these (terrorists) are very capable actors," he added.

Benjamin said he didn't believe eliminating al-Qaida meant the endgame.

"I think it (terrorism) is a very durable ideology. It appears that their ranks are growing," he said.

The events of Sept. 11 transformed life for Muslims in the United States, and the flow of immigrants from countries like Egypt, Pakistan and Morocco thinned sharply.

But five years later, as the United States wrestles with questions of terrorism, civil liberties and immigration control, Muslims appear to be moving here again in surprising numbers, according to statistics collected by the Department of Homeland Security and the Census Bureau.

Immigrants from predominantly Muslim countries in the Middle East, North Africa and Asia are planting new roots in states from Virginia to Texas to California.

In 2005, more people from Muslim countries became legal permanent United States residents - nearly 96,000 - than in any year in the previous two decades.

More than 40,000 of them were admitted last year, the highest annual number since the terrorist attacks, according to data on 22 countries provided by the Department of Homeland Security.

Many have made the journey unbowed by tales of immigrant hardship, and despite their own opposition to American policy in the Middle East. They come seeking the same promise that has drawn foreigners to the United States for many decades, according to a range of experts and immigrants: economic opportunity and political freedom.

Those lures, both powerful and familiar, have been enough to conquer fears that America is an inhospitable place for Muslims.

"America has always been the promised land for Muslims and non-Muslims," said Behzad Yaghmaian, an Iranian exile and author of "Embracing the Infidel: Stories of Muslim Migrants on the Journey West." "Despite Muslims' opposition to America's foreign policy, they still come here because the United States offers what they're missing at home."

For Ms. Fatima, it was the freedom to dress as she chose and work as a security guard. For Mr. Youssef, it was the chance to earn a master's degree.

He came in spite of the deep misgivings that he and many other Egyptians have about the war in Iraq and the Bush administration. In America, he said, one needs to distinguish between the government and the people.

"Who am I dealing with, Bush or the American public?" he said. "Am I dealing with my future in Egypt or my future here?"

Muslims have been settling in the United States in significant numbers since the mid-1960's, after immigration quotas that favored Eastern Europeans were lifted. Spacious mosques opened in Chicago, Los Angeles and New York as a new, highly educated Muslim population took hold.

Over the next three decades, the story of Muslim migration to the United States was marked by growth and prosperity. A larger percentage of immigrants from Muslim countries have graduate degrees than other American residents, and their average salary is about 20 percent higher, according to census data.

But Sept. 11 altered the course of Muslim life in America. Mosques were vandalized. Hate crimes rose. Deportation proceedings began against thousands of men.

Some Muslims changed their names to avoid job discrimination, making Mohammed "Moe," and Osama "Sam." Scores of families left for Canada.

Yet this period also produced something strikingly positive, in the eyes of many Muslims: they began to mobilize politically and socially. Across the country, grass-roots groups expanded to educate Muslims on civil rights, register them to vote and lobby against new federal policies such as the Patriot Act.

"There was the option of becoming introverted or extroverted," said Agha Saeed, national chairman of the American Muslim Task Force on Civil Rights and Elections, an umbrella organization in Newark, Calif. "We became extroverted."

In some ways, new Muslim immigrants may be better off in the post-9/11 America they encounter today, say Muslim leaders: Islamic centers are more organized, and resources like English instruction and free legal help are more accessible.

But outside these newly organized mosques, life remains strained for many Muslims. To avoid taunts, women are often warned not to wear head scarves in public, as was Rubab Razvi, 21, a Pakistani who arrived in Brooklyn nine months ago. (She ignored the advice, even though people stare at her on the bus, she said.) Muslims continue to endure long waits at airports, where they are often tagged for questioning.

To some longtime immigrants, the life embraced by newcomers will never compare to the peaceful era that came before.

"They haven't seen the America pre-9/11," said Khwaja Mizan Hassan, 42, who left Bangladesh 30 years ago. He rose to become the president of Jamaica Muslim Center, a mosque in Queens, and has a comfortable job with the New York City Department of Probation.

But after Sept. 11, he was stopped at Kennedy Airport because his name matched one on a watch list.

A Drop, Then a Surge

Up to six million Muslims live in the United States, by some estimates. While the Census Bureau and the Department of Homeland Security do not track religion, both provide statistics on immigrants from predominantly Muslim countries. It is presumed that many of these immigrants are Muslim, but people of other faiths, such as Iraqi Chaldeans and Egyptian Copts, have also come in appreciable numbers.

Immigration from these regions slowed considerably after Sept. 11. Fewer people were issued green cards and nonimmigrant visas. By 2003, the number of immigrants arriving from 22 Muslim countries had declined by more than a third. For students, tourists and other nonimmigrants from these countries, the drop was even more dramatic, with total visits down by nearly half.

The falloff affected immigrants from across the post-9/11 world as America tightened its borders, but it was most pronounced among those moving here from Pakistan, Morocco, Iran and other Muslim nations.

Several factors might explain the drop: more visa applications were rejected due to heightened security procedures, said officials at the State Department and Department of Homeland Security; and fewer people applied for visas.

But starting in 2004, the numbers rebounded. The tally of people coming to live in the United States from Bangladesh, Turkey, Algeria and other Muslim countries rose by 20 percent, according to an analysis of Census Bureau data.

The uptick was also notable among foreigners with nonimmigrant visas. More than 55,000 Indonesians, for instance, were issued those visas last year, compared with roughly 36,000 in 2002.

The rise does not reflect relaxed security measures, but a higher number of visa applications and greater efficiency in processing them, said Chris Bentley, a spokesman for United States Citizenship and Immigration Services, part of Homeland Security.

Like other immigrants, Muslims find their way to the United States in myriad ways: they come as refugees, or as students and tourists. Others arrive with immigrant visas secured by relatives here. A lucky few win the green-card lottery.

Ahmed Youssef, 29, never thought he would be among the winners. But in 2003, Mr. Youssef, who taught Arabic in Egypt, was one of 50,000 people randomly chosen from 9.5 million applicants around the world.

As he prepared to leave Benha, a city north of Cairo, some friends asked him how he could move to a country that is "killing people in Iraq and Afghanistan," he recalled. But others who had been to the United States encouraged him to go.

He arrived in May 2005, and he found work loading hot dog carts from sunrise to sundown. He shared an apartment in Washington Heights with other Egyptians, but for the first month, he never saw his neighborhood in daylight.

"I joked to my roommates, 'When am I going to see America?' " said Mr. Youssef, a slight man with thinning black hair and an easy smile.

Only three months later, when he began selling hot dogs on Seventh Avenue, did Mr. Youssef discover his new country.

He missed hearing the call to prayer, and thought nothing of unrolling his prayer rug beside his cart until other vendors warned him against it. He could be mistaken for an extremist, they told him.

Eventually, Mr. Youssef found a job as the secretary of the Islamic Center of Jersey City. He plans to apply to a master's program at Columbia University, specializing in Arabic. For now, he lives in a spare room above the mosque. Near his bed, he keeps a daily log of his prayers. If he makes them on time, he writes "Correct" in Arabic. "I am much better off here than selling hot dogs," he said.

Awash in American Flags

Nur Fatima landed in Midwood, Brooklyn, at a propitious time. Had she come three years earlier, she would have seen a neighborhood in crisis.

Hundreds of Pakistani immigrants disappeared after being asked to register with the government. Thirty shops closed along a stretch of Coney Island Avenue known as Little Pakistan. The number of new Urdu-speaking pupils at the local elementary school, Public School 217, dropped by half in the 2002-3 school year.

But then Little Pakistan got organized. A local businessman, Moe Razvi, converted a former antique store into a community center offering legal advice, computer classes and English instruction. Local Muslim leaders began meeting with federal agents to soothe relations.

The annual Pakistan Independence Day parade is now awash in American flags.

It is a transformation seen in Muslim immigrant communities around the nation.

"They have to prove that they are living here as Muslim Americans rather than living as Pakistanis and Egyptians and other nationalities," said Zahid H. Bukhari, the director of the American Muslim Studies Program at Georgetown University.

Ms. Fatima arrived in Brooklyn from Pakistan in March with an immigrant visa. She began by taking English classes at Mr. Razvi's center, the Council of Peoples Organization.

She has heard stories of the neighborhood's former plight but sees a different picture.

"This is a land of opportunity," Ms. Fatima said. "There is equality for everyone."

Five days after she came to Brooklyn, Ms. Fatima removed her head scarf, which she had been wearing since she was 10. She began to change her thinking, she said: She liked living in a country where people respected the privacy of others and did not interfere with their religious or social choices.

"I came to the United States because I want to improve myself," she said. "This is a second birth for me."

"Here you've got a guy who's gone off the net and is hiding in some of the most formidable terrain in one of the most remote parts of the world surrounded by people he trusts implicitly," said T. McCreary, spokesman for the National Counterterrorism Center. "And he stays off the net and is probably not mobile. That's an extremely difficult problem."

Intelligence officials think that bin Laden is hiding in the northern reaches of the autonomous tribal region along the Afghanistan-Pakistan border. This calculation is based largely on a lack of activity elsewhere and on other intelligence, including a videotape, obtained exclusively by the CIA and not previously reported, that shows bin Laden walking on a trail toward Pakistan at the end of the battle of Tora Bora in December 2001, when U.S. forces came close but failed to capture him.

Many factors have combined in the five years since the Sept. 11, 2001, attacks to make the pursuit more difficult. They include the lack of CIA access to people close to al-Qaeda's inner circle; Pakistan's unwillingness to pursue him; the reemergence of the Taliban and al-Qaeda in Afghanistan; the strength of the Iraqi insurgency, which has depleted U.S. military and intelligence resources; and the U.S. government's own disorganization.

But the underlying reality is that finding one person in hiding is difficult under any circumstances. Eric Rudolph, the confessed Olympics and abortion clinic bomber, evaded authorities for five years, only to be captured miles from where he was last seen in North Carolina.

It has been so long since there has been anything like a real close call that some operatives have given bin Laden a nickname: "Elvis," for all the wishful-thinking sightings that have substituted for anything real.

After playing down bin Laden's importance and barely mentioning him for several years, Bush last week repeatedly invoked his name and quoted from his writings and speeches to underscore what Bush said is the continuing threat of terrorism.

Many terrorism experts, however, say the importance of finding bin Laden has diminished since Bush first pledged to capture him "dead or alive" in the aftermath of the Sept. 11 attacks. Terrorists worldwide have repeatedly shown they no longer need him to organize or carry out attacks, the experts say. Attacks in Europe, Asia and the Middle East were perpetrated by homegrown terrorists unaffiliated with al-Qaeda.

"Will his capture stop terrorism? No," Rep. Jane Harman (D-Calif.), vice chairman of the House Intelligence Committee, said in a recent interview. "But in terms of a message to the world, it's a huge message."

Despite a lack of progress, at CIA headquarters bin Laden and his deputy, Ayman al-Zawahiri, are still the most wanted of the High Value Targets, referred to as "HVT 1 and 2." The CIA station in Kabul still offers a briefing to VIP visitors that declares: "We are here for the hunt!" -- a reminder that finding bin Laden is a top priority.

Gary Berntsen, the former CIA officer who led the first and last hunt for bin Laden at Tora Bora, in December 2001, says, "This could all end tomorrow." One unsolicited walk-in. One tribesman seeking to collect the $25 million reward. One courier who would rather his kids grow up in the United States. One dealmaker, "and this could all change," Berntsen said.

Bin Laden Still Alive

On the videotape obtained by the CIA, bin Laden is seen confidently instructing his party how to dig holes in the ground to lie in undetected at night. A bomb dropped by a U.S. aircraft can be seen exploding in the distance. "We were there last night," bin Laden says without much concern in his voice. He was in or headed toward Pakistan, counterterrorism officials think.

That was December 2001. Only two months later, Bush decided to pull out most of the special operations troops and their CIA counterparts in the paramilitary division that were leading the hunt for bin Laden in Afghanistan to prepare for war in Iraq, said Flynt L. Leverett, then an expert on the Middle East at the National Security Council.

"I was appalled when I learned about it," said Leverett, who has become an outspoken critic of the administration's counterterrorism policy. "I don't know of anyone who thought it was a good idea. It's very likely that bin Laden would be dead or in American custody if we hadn't done that."

Several officers confirmed that the number of special operations troops was reduced in March 2002.

White House spokeswoman Michele Davis said she would not comment on the specific allegation. "Military and intelligence units move routinely in and out," she said. "The intelligence and military community's hunt for bin Laden has been aggressive and constant since the attacks."

The Pakistani intelligence service, notoriously difficult to trust but also the service with the best access to al-Qaeda circles, is convinced bin Laden is alive because no one has ever intercepted or heard a message mourning his death. "Al-Qaeda will mourn his death and will retaliate in a big way. We are pretty sure Osama is alive," Pakistan's interior minister, Aftab Khan Sherpao, said in a recent interview with The Washington Post.

Pakistani intelligence officials also say they think bin Laden remains actively involved in al-Qaeda activities. They cite the interrogations of Ahmed Khalfan Ghailani, a key planner of the bombings of two U.S. embassies in East Africa in 1998, and Abu-Faraj al-Libbi, who served as a communications conduit between bin Laden and senior al-Qaeda operatives until his capture last year.

Libbi and Ghailani, who was arrested in Pakistan in July 2004, were the last two people taken into custody to have met with and taken orders from Zawahiri and to hear directly from bin Laden. "Both Ghailani and Libbi were informed that Osama was well and alive and in the picture by none other than Zawahiri himself," one Pakistani intelligence official said.

Two Pakistani intelligence officials recently interviewed in Karachi said that the last time they received firsthand information on bin Laden was in April 2003, when an arrested al-Qaeda leader, Tawfiq bin Attash, disclosed having met him in the Khost province of Afghanistan three months earlier.

Attash, who helped plan the 2000 USS Cole bombing, told interrogators that the meeting took place in the Afghan mountains about two hours from the town of Khost.

By then, Pakistan was the United States' best bet for information after an infusion of funds from the U.S. intelligence community, particularly in the area of expensive NSA eavesdropping equipment.

"For technical intelligence ISI (Inter-Services Intelligence) works hand in hand with the NSA," a senior Pakistani intelligence official said. "The U.S. assistance in building Pakistan's capabilities for technical intelligence since 9/11 is superb."

Since early 2002, the United States has stationed a small number of personnel from the NSA and the CIA near where bin Laden may be hiding. They are embedded with counterterrorism units of the Pakistan army's elite Special Services Group, according to senior Pakistani intelligence officials.

The NSA and other specialists collect imagery and electronic intercepts that their CIA counterparts then share with the Pakistani units in the tribal areas and with the province of Baluchistan to the south.

But even with sophisticated technology, the local geography presents formidable obstacles. In a land of dead-end valleys, high peaks and winding ridge lines, it is easy to hide within the miles of caves and deep ravines, or to live unnoticed in mud-walled compounds barely distinguishable from the surrounding terrain.

The Afghan-Pakistan border is about 1,500 miles. Pakistan deploys 70,000 troops there. Its army had never entered the area until October 2001, more than a half century after Pakistan's founding.

Pakistani Sources Lost

A Muslim country where many consider bin Laden a hero, Pakistan has grown increasingly reluctant to help the U.S. search. The army lost its best source of intelligence in 2004, after it began raids inside the tribal areas. Scouts with blood ties to the tribes ceased sharing information for fear of retaliation.

They had good reason. At least 23 senior anti-Taliban tribesmen have been assassinated in South and North Waziristan since May 2005. "Al-Qaeda footprints were found everywhere," Interior Minister Sherpao said in a recent interview. "They kidnapped and chopped off heads of at least seven of these pro-government tribesmen."

Pakistani and U.S. counterterrorism and military officials admit that Pakistan has now all but stopped looking for bin Laden. "The dirty little secret is, they have nothing, no operations, without the Paks," one former counterterrorism officer said.

Last week, Pakistan announced a truce with the Taliban that calls on the insurgent Afghan group to end armed attacks inside Pakistan and to stop crossing into Afghanistan to fight the government and international troops. The agreement also requires foreign militants to leave the tribal area of North Waziristan or take up a peaceable life there.

In Afghanistan, the hunt for bin Laden has been upstaged by the reemergence of the Taliban and al-Qaeda, and by Afghan infighting for control of territory and opium poppy cropland.

Lt. Gen. John R. Vines, who commanded U.S. troops in Afghanistan in 2003, said he thinks bin Laden kept close to the border, not wandering far into either country. That belief is still current among military and intelligence analysts.

"We believe that he held to a pretty narrow range of within 15 kilometers of the border," said Vines, who now commands the XVIII Airborne Corps, "so that if the Pakistanis, for whatever reason, chose to do something to him, he could cross into Afghanistan and vice versa."

He said he thinks bin Laden's protection force "had a series of outposts with radios that could alert each other" if helicopters were coming or other troop movements were evident.

Pakistani military officials in Wana, the capital of South Waziristan, described bin Laden as having three rings of security, each ring unaware of the movements and identities of the other. Sometimes they communicated with specially marked flashlights. Sometimes they dressed as women to avoid detection by U.S. spy planes.

Pakistan will permit only small numbers of U.S. forces to operate with its troops at times and, because their role is so sensitive politically, it officially denies any U.S. presence. A frequent complaint from U.S. troops is that they have too little to do. The same complaint is also heard from U.S. forces in Afghanistan, where there were few targets to go after.

Although the hunt for bin Laden has depended to a large extent on technology, until recently unmanned aerial vehicles (UAVs) were in short supply, especially when the war in Iraq became a priority in 2003.

In July 2003, Vines said that U.S. forces under his command thought they were close to striking bin Laden, but had only one drone to send over three possible routes he might take. "A UAV was positioned on the route that was most likely, but he didn't go that way," Vines said. "We believed that we were within a half-hour of possibly getting him, but nothing materialized."

Faced with the most sophisticated technology in the world, bin Laden has gone decidedly low-tech. His 23 video or audiotapes in the last five years are thought to have been hand-carried to news outlets or nearby mail drops by a series of couriers who know nothing about the contents of their deliveries or the real identity of the sender, a simple method used by spies and drug traffickers for centuries.

"They are really good at operational security," said Ben Venzke, chief executive officer of IntelCenter, a private company that analyzes terrorist information and has obtained, analyzed and published all bin Laden's communiques. "They are very good at having enough cut-outs" to move videos into circulation without detection. "It's some of the simplest things to do."

Uncertain Command Structure

Bureaucratic battles slowed down the hunt for bin Laden for the first two or three years, according to officials in several agencies, with both the Pentagon and the CIA accusing each other of withholding information. Defense Secretary Donald H. Rumsfeld's sense of territoriality has become legendary, according to these officials.

In early November 2002, for example, a CIA drone armed with a Hellfire missile killed a top al-Qaeda leader traveling through the Yemeni desert. About a week later, Rumsfeld expressed anger that it was the CIA, not the Defense Department, that had carried out the successful strike.

"How did they get the intel?" he demanded of the intelligence and other military personnel in a high-level meeting, recalled one person knowledgeable about the meeting.

Gen. Michael V. Hayden, then director of the National Security Agency and technically part of the Defense Department, said he had given it to them.

"Why aren't you giving it to us?" Rumsfeld wanted to know.

Hayden, according to this source, told Rumsfeld that the information-sharing mechanism with the CIA was working well. Rumsfeld said it would have to stop.

A CIA spokesman said Hayden, now the CIA director, does not recall this conversation. Pentagon spokesman Bryan Whitman said, "The notion that the department would do anything that would jeopardize the success of an operation to kill or capture bin Laden is ridiculous." The NSA continues to share intelligence with the CIA and the Defense Department.

At that time, Rumsfeld was putting in place his own aggressive plan, led by the U.S. Special Operations Command (SOCOM), to dominate the hunt for bin Laden and other terrorists. The overall special operations budget has grown by 60 percent since 2003 to $8 billion in fiscal year 2007.

Rows and rows of temporary buildings sprang up on SOCOM's parking lots in Tampa as Rumsfeld refocused the mission of a small group of counterterrorism experts from long-term planning for the war on terrorism to manhunting. The group "went from 20 years to 24-hour crisis-mode operations," one former special operations officer said. "It went from planning to manhunting."

In 2004, Rumsfeld finally won the president's approval to put SOCOM in charge of the "Global War on Terrorism."

Today, however, no one person is in charge of the overall hunt for bin Laden with the authority to direct covert CIA operations to collect intelligence and to dispatch JSOC units. Some counterterrorism officials find this absurd. "There's nobody in the United States government whose job it is to find Osama bin Laden!" one frustrated counterterrorism official shouted. "Nobody!"

"We work by consensus," explained Brig. Gen. Robert L. Caslen Jr., who recently stepped down as deputy director of counterterrorism under the Joint Chiefs of Staff. "In order to find Osama bin Laden, certain departments will come together. . . . It's not that effective, or we'd find the guy, but in terms of advancing United States power for that mission, I think that process is effective."

But Lt. Gen. Stanley A. McChrystal, the JSOC commander since 2003, has become the de facto leader of the hunt for bin Laden and developed a good working relationship with the CIA to the extent that he recently was able to persuade the former station chief in Kabul to become his special assistant. He asks for targets from the CIA, and it tries to comply. "We serve the military," one intelligence officer said.

McChrystal's troops have shuttled between Afghanistan and Iraq, where they succeeded in killing al-Qaeda leader Abu Musab al-Zarqawi and killed or captured dozens of his followers.

Under McChrystal, JSOC has improved its ability to quickly turn captured documents, computers and cellphones into leads and then to act upon them, while waiting for more analysis from CIA or SOCOM.

Industry experts and military officers say they are being aided by computer forensic field kits that let technicians retrieve information from surviving hard drives, cellphones and other electronic devices, as was the case in the Zarqawi strike.

McChrystal, who has commanded JSOC since 2003, now has the authority to go after bin Laden inside Pakistan without having to seek permission first, two U.S. officials said.

"The authority," one knowledgeable person said, "follows the target," meaning that if the target is bin Laden, the stakes are high enough for McChrystal to decide any action on his own. The understanding is that U.S. units will not enter Pakistan, except under extreme circumstances, and that Pakistan will deny giving them permission.

Such was the case in early January, when JSOC troops clandestinely entered the village of Saidgai, two officials familiar with the operation said, and Pakistan protested.

A week later, acting on what Pakistani intelligence officials said was information developed out of Libbi's interrogation, the CIA ordered a missile strike against a house in the village of Damadola, about 120 miles northwest of Islamabad, where Pakistani and American officials thought Zawahiri to be hiding.

The missile killed 13 civilians and several suspected terrorists. But Zawahiri was not among them. The strike "could have changed the destiny of the war on terror. Zawahiri was 100 percent sure to visit Damadola . . . but he disappeared at the last moment," one Pakistani intelligence official said.

Tens of thousands of Pakistanis staged an angry anti-American protest near Damadola, shouting, "Death to America!"

"Once again, we have lost track of Ayman al-Zawahiri," the Pakistani intelligence official said in a recent interview. "He keeps popping on television screens. It's miserable, but we don't know where he or his boss are hiding."