That's lower than in the other countries polled - Canada, France, Germany, South Korea, Spain and the United Kingdom, where three-fourths or more in each country felt the vote count is accurate.

"If we're going to have an effective democracy, we can't lose confidence in the institutions that deal with the votes," said Gabriel Nunez, a 39-year-old sales clerk in Mexico City.

In Mexico, Italy and the United States, recent contested elections left one side feeling cheated.

- In Mexico this past summer, ruling party candidate Felipe Calderon was proclaimed the winner after the country's top electoral court rejected claims by leftist candidate Andres Manual Lopez Obrador of widespread fraud. By the end of the year, Mexicans will have an elected president, and the man he beat will have been "inaugurated" president by his followers.

- In Italy's parliamentary elections last April, outgoing Premier Silvio Berlusconi alleged the vote was marred by irregularities and for weeks refused to accept the narrow-margin victory of Romano Prodi's center-left coalition.

- In the United States, the 2000 election was contested for more than a month before the Supreme Court ended the dispute, enabling Republican George W. Bush to be certified the winner over Democrat Al Gore. The 2004 election had enough problems to bring back memories from four years earlier.

- Germans had a close election in 2005 but worked out a compromise and the German people accepted the count with little outcry.

The U.S. complaints in 2000 and again in 2004 left Charlotte Blum, an independent voter from Fairfax, Vt., with doubts about the accuracy of the vote count. "People were asking for recounts," she said of the 2004 voting. "It's a bad atmosphere for the country."

The doubts come at a time that voter turnout has been sliding in many different countries.

Only half in the United States said they always vote, the lowest level in any of the nine countries polled. More than seven in 10 in Canada, France and Germany say they always vote, with almost that many in Spain and Britain saying that.

Voter turnout is traditionally higher in many European democracies than in the United States, and some voting analysts blame U.S. voter registration laws that put much of the burden on the voter to register.

Voter turnout has been dropping in many democracies, however, and the lack of interest among young adults is frequently cited.

For example:

- In the United Kingdom's 2001 election, just 59 percent of registered voters cast a ballot, the lowest turnout since 1918. The 2005 national elections brought out 61 percent of voters, recording a slight upturn in a trend that has been moving down.

- Voter turnout in Canada has waned steadily over recent years, dropping from 75 percent of registered voters in 1988 to an all-time low of 60 percent in the June 2004 election.

- Turnout for German parliamentary elections usually hovers around 80 percent, matching a post-World War II low last year with about 78 percent of the electorate turning out - still high for most democracies.

- In France, voter turnout has been dropping, especially in parliamentary elections, but the 2002 results when right-wing candidate Jean-Marie Le Pen forced a runoff - eventually won by President Jacques Chirac - were a shocker for many.

Margot Gillouard, a 19-year-old student in Paris who would be voting for the first time in 2007, is aware of the high stakes in the French elections. "When you see what happened the last time, I wouldn't miss it for anything," she said.

Turnout in the United States has been dropping over the last few decades, but was higher in 2004 when 122 million, or 62 percent of the voting age population, turned out in the presidential contest.

The drop in voting levels is widespread and often involves young people, said Bruce Cain, a political scientist at University of California-Berkeley.

"There seems to be a general wave of demobilization, a problem of disengagement," he said, noting that voting is marked by "peaks and valleys." "A major part of it in many countries is young people. They move a lot, they don't have a vested interest in the society."

Compulsory voting is one approach that scattered countries have tried over the years - though few enforce the law. That approach to improving voter turnout was backed by 63 percent in France, 59 percent in Mexico and 58 percent in Britain.

Only 33 percent in the United States favored that approach, according to the polling of about 1,000 people in each of the countries. The telephone polls, conducted between Sept. 8 and Oct. 1, have margins of sampling error of plus or minus 3 percentage points in each country.

Skeptical attitudes about how much an individual's vote counts runs high in European democracies - with totals ranging from 32 percent in Germany and 51 percent in Spain saying they feel their vote doesn't count.

But occasional election problems don't upset Giancarlo Rossi, a 60-year-old export manager in Rome, who agrees with six in 10 in his country that he's confident his vote counts.

"Little tricks can happen often," he said, "but they don't influence the overall result."

He declined to identify the specific Republican campaign Wednesday, citing the ongoing investigation. The Los Angeles Times and The Orange County Register both reported Thursday that the investigation appeared to be focused on the campaign of Tan D. Nguyen, a Republican challenger to Democratic U.S. Rep. Loretta Sanchez.

The letter, written in Spanish, tells recipients: "You are advised that if your residence in this country is illegal or you are an immigrant, voting in a federal election is a crime that could result in jail time."

In fact, immigrants who are naturalized U.S. citizens can vote.

Complaints about the letters this week prompted state and federal investigations, and Barankin said investigators had been questioning people in Orange County.

The two newspapers reported state investigators had found the location where the letters were printed and mailed to an estimated 14,000 Democratic voters in central Orange County. The Los Angeles Times, citing an unnamed source, said authorities had interviewed Nguyen at his office.

Nguyen did not return messages left by The Associated Press or either newspaper.

Sanchez said in an interview Thursday on Univision that the sender should be punished for stating that immigrants can't vote. It would be unfortunate if the person responsible was another immigrant, she said.

"What a shame, really, that this is still happening in the United States today," Sanchez said.

The owner of Huntington Beach-based Mailing Pros, Christopher West, told The Orange County Register that he was hired to do the mailings but didn't know what they said and didn't know any laws were being broken when the mailer was sent. He said he gave investigators the name of the person who hired him.

"I'm the one that processed it, and I don't read Spanish," West said. "Until the investigator read it to me, I didn't know the content."

Scott Baugh, chairman of the Orange County Republican Party, condemned the letter as "an obnoxious, grotesque piece of work."

"Regardless of who did it - Republican or Democrat - if it's a crime, then whoever did it should be prosecuted," Baugh said.

A group of six Vietnamese-American political candidates running for offices in Orange County issued a joint statement saying: "The content of this mailer is offensive to the immigrant voters, regardless of their ethnicity."

The note's letterhead resembles that of an anti-illegal immigration group, California Coalition for Immigration Reform, but group leader Barbara Coe said she told investigators for the attorney general's office Wednesday that her group didn't authorize the letter and she didn't know who sent it.

"The letterhead was altered and I've never head of any Sergio Ramirez," the name signed to the letter, Coe said.

Numerous political leaders including Gov. Arnold Schwarzenegger have denounced the letter and called for the investigations.

Arizona, California, Georgia, Indiana, Maryland, Mississippi, Missouri, North Carolina, Ohio and Pennsylvania are among the states considered most likely to experience difficulties, according to voting experts who have been tracking the technology and other election changes.

"We've got new laws, new technology, heightened partisanship and a growing involvement of lawyers in the voting process," said Tova Wang, who studies elections for the Century Foundation, a nonpartisan research group. "We also have the greatest potential for problems in more places next month than in any voting season before."

Election officials in many of the states are struggling with delays in the delivery of machines before the election as old-fashioned lever and punch-card machines are phased out. A chronic shortage of poll workers, many of them retirees uncomfortable with new technology, has worsened matters.

Wendy S. Noren, the top election official for Boone County, Mo., which includes Columbia, said delays in the delivery of new machines had left her county several weeks behind schedule and with 600 poll workers yet to be trained. Ms. Noren said she also had not yet been provided with the software coding she needed to print the training manuals.

"I think we will make it," she said, "but my staff is already at the point of passing out, and the sprint is just starting."

New computerized registration rolls and litigation over new voter identification laws in states like Arizona, Georgia, Indiana and Missouri have left many poll workers and voters unclear about the rules, including whether they are in effect, as the courts have blocked many of the new laws.

"We're expecting arguments at the polls in these states that will slow everything down and probably cause large numbers of legitimate voters to be turned away or to be forced to vote on provisional ballots," said Barbara Burt, an elections reform director for Common Cause.

Meanwhile, votes in about half of the 45 most competitive Congressional races, including contests in Florida, Georgia and Indiana, will be cast on electronic machines that provide no independent means of verification.

"In a close race, a machine error in one precinct could leave the results in doubt and the losing candidates won't be able to get a recount," said Warren Stewart, policy director for VoteTrustUSA, an advocacy group that has criticized electronic voting.

Deborah L. Markowitz, president of the National Association of Secretaries of State, was less inclined to sound the alarm. She said that since it was not a presidential election year and many states had encouraged voting by mail, fewer people would turn up at the polls than in 2004.

With computerized registration rolls, Ms. Markowitz said, there will be far fewer people incorrectly excluded from the new databases compared with when registration rolls were on paper.

"There will be isolated incidents, there is no doubt about that," she said. "But over all the system will move faster and with fewer problems."

Charles Stewart, head of the political science department at the Massachusetts Institute of Technology, published a study this year indicating that from 2000 to 2004, new technology helped reduce the number of improperly marked ballots by about one million votes.

"If you think things are bad and worrisome now, they were much worse before 2000," Mr. Stewart said, adding that breakdowns in the mechanics of voting are simply more highlighted, not more prevalent.

Still, this is a year of firsts for some local election officials. Cherie Poucher, elections director for Wake County, N.C., which includes Raleigh, said she expected 350,000 voters on Election Day, up from the 30,000 in the May primary. She worries that the county's 218 optical scan machines may be unable to handle the increased load. During the primary, 12 of the new machines would not boot up and needed to be replaced.

In October 1994, when Democrats held congressional majorities, Congress had a 24 percent job approval, NBC said. Democrats lost 52 House and 8 Senate seats in the 1994 midterm elections.

NBC said the poll indicates people have been paying attention to the issues they are hearing about -- from Iraq and Bob Woodward's new book on the Bush administration's handling of the war to the unfolding scandal over former Florida Rep. Mark Foley's e-mail messages to teenage congressional aides.

The poll numbers and President George W. Bush's own job approval ratings, which have been mired in the 30 percent range, are an ominous sign for a party trying to maintain control of Congress, NBC said.

Bush had a job approval rating of 38 percent, down 1 percentage point from a previous NBC News/Wall Street Journal poll released earlier this month after the Foley news first broke, NBC said.

Asked who they planned to vote for in the congressional election, 37 percent of those polled said Republicans and 52 percent said Democrats. The 15 percent difference was the highest disparity ever in the poll and up from a 9-point difference a month ago, NBC said.

The poll of 1,006 registered voters was taken from October 13-16 and has a margin of error of plus or minus 3.1 percentage points.