Despite optimistic claims by American officials that the tide is finally turning against cancer, a growing number of patient advocates and researchers say they are discouraged by continuing slow progress in the 36-year-war against the disease in the United States.

Many of the most anticipated new drugs have extended patients' lives by only a few months, often at great expense, they say, and researchers still do not understand what makes the disease spread to other parts of the body - the cause of 90 percent of cancer deaths.

Although the number of deaths from cancer has declined slightly since 2002, cancer specialists say that reflects earlier detection of the disease as well as lifestyle changes, like quitting smoking, rather than dramatic improvements in treatment.

For many types of cancer, once the disease has metastasized the patient's chance of survival is not much better than when President Richard Nixon declared "war" on the disease in 1971, triggering a cumulative $69 billion U.S. government investment in cancer research. A patient whose lung cancer has spread to other organs, for example, has a 3 percent chance of surviving five years after the original diagnosis.

With government financing for cancer research frozen since 2003, critics say the pace of progress could slow even more as young researchers leave the field.

This year, the disease is expected to kill 560,000 Americans, putting cancer on a course to become the number one killer in the United States in the next few years.

Heart disease, the current leading cause of death, has become almost 50 percent less lethal since the early 1970s, thanks to breakthroughs like artery-clearing stents and drugs for reducing cholesterol.

"I would have expected us to be doing a heck of a lot better based on the investment that we've made and based on the prevalence of the disease," said Kathy Giusti, founder of the Multiple Myeloma Research Foundation, an organization based in Connecticut and one of several groups pressing researchers to develop better cancer medications more quickly.

When she was diagnosed with multiple myeloma, a rare blood cancer, in 1996, Giusti said, "the treatments they offered me were exactly the same ones they offered my grandfather when he had the disease."

Advocates acknowledge that treatment is improving for some cancers - four new medications have been approved for multiple myeloma alone in the past five years, in part thanks to Giusti's efforts, while drugs like Herceptin have extended the lives of women with breast cancer. But that is not enough to ease the fears of the 1.4 million people who will learn this year that they have cancer. And after cancer spreads from its original location, doctors can only slow down the disease, not cure it.

Moreover, studies show that many patients are not sharing in the modest progress, including those who have less common cancers as well as people with limited access to health care. Black women with advanced breast cancer typically live no longer now than in 1988, while life expectancy after diagnosis of white women has grown to 27 months from 20 months in the same period. The researchers said the likely cause of the discrepancy was poor access to the latest treatments.

"I have never been as worried about our nation's commitment to the war on cancer as I am today," said Nancy Brinker, a breast cancer survivor and founder of an advocacy group called Susan G. Komen for the Cure, in a speech to thousands of cancer specialists in Chicago in June. She called on researchers to come up with better medicines: "There is a Great Divide between discovery and delivery," she said, "when we celebrate as 'breakthroughs' treatments that cost $50,000 and that extend life, at most, a few months. This is progress?"

Ironically, the pessimism comes at a time when knowledge about cancer is exploding and when officials at the National Cancer Institute and the American Cancer Society talk hopefully about a day when doctors can stop cancer without the toxic side effects of traditional radiation and chemotherapy treatment. In 2005, Andrew von Eschenbach, who was then the director of the National Cancer Institute, was so encouraged he set a goal of eliminating cancer by 2015.

Today, the directors of both institutions are careful not to declare victory, but they say they see clear signs of improvement, including the slight decline in the number of deaths from cancer that began in 2003 and continued through 2004, the latest year for which data are available. With a record number of cancer drugs now undergoing human testing, many cancer specialists say the future for patients looks brighter than it has in years.

"The evidence is unmistakable: We are truly turning the tide in the cancer battle," John Seffrin, chief executive of the Cancer Society, said in an October statement celebrating the declining death rate.

But critics of the war on cancer say they have heard this sunny rhetoric before, beginning in 1969, when a powerful coalition of doctors and scientists ran a full-page ad in The New York Times urging Nixon to "conquer cancer by America's 200th birthday" in 1976. For decades, promising cancer treatments have fizzled and officials have used statistics, sometimes misleadingly, to make the case that the war is going well.

The most-used measure of progress is the five-year survival rate - the percentage of patients who live five years from the date of diagnosis. But the wider use of screening tests for some cancers has led to tumors being found earlier, increasing the years patients live with cancer on average - the "survival rate" - without actually extending their lives.

Americans "have heard the same song for a generation - that we're finally making progress against the disease, that we've turned the corner. And it doesn't jibe with what they see and experience in their own lives," said Clifton Leaf, a survivor of Hodgkin's disease and a former Fortune Magazine editor who is writing a book on the "dysfunctional" cancer research industry.

Leaf believes that researchers have created their own problems by avoiding the toughest issue in cancer. The National Cancer Institute does not track how much of its budget goes toward metastasis research, but Leaf found that only 0.5 percent of institute grant proposals have focused on stopping the spread of cancer since the efforts to fight cancer began.

Today, doctors have few medicines that can shrink large metastatic tumors, and, for most cancers, no reliable way to tell patients after cancer treatment that the disease will or will not spread. The difference is profound: A patient who has localized colon cancer has a 90 percent chance of being alive in five years. But if the cancer has spread to distant parts of his body, the five-year survival rate drops to 10 percent.

"People come out of cancer surgery feeling like time bombs" because they do not know whether the disease will return, said Bruce Zetter, chief scientific officer at Children's Hospital Boston, who specializes in metastasis.