Democrats won control of the House of Representatives yesterday for the first time in more than a decade, but it was still in doubt early this morning whether the party would gain enough Senate seats to effect a complete takeover of the legislative branch.

The San Francisco Democrat who is expected to become Speaker of the House, Nancy Pelosi, said Americans had “voted for change.”

She said that Democrats are “ready to lead”and she said they would govern “working together with the administration and the Republicans in Congress, in partnership, not in partisanship.” She called for a new direction in the war in Iraq.

“This is one great victory for America,” the head of the Democratic Senatorial Campaign Committee, Senator Schumer, told supporters at an election night party in Washington. “We have taken back the House…. In terms of the Senate majority, the night is still young.”

Soon after 11 p.m., when polls closed in many Western states, television networks projected that Democrats would capture at least the 15 seats needed to form a majority. In the Senate, Democrats needed to pick up six seats. Missouri, Montana, Ohio, Pennsylvania, Rhode Island, Tennessee, and Virginia offered the best prospects.

Democratic candidates defeated incumbent Republicans in Ohio, Pennsylvania, and Rhode Island, leaving the battle to be fought in the remaining four states.

As of press time, there were no projections of winners in the other tight Senate contests.

An exit poll taken for television networks and the Associated Press offered gloomy signs for Republicans. About 37% of those surveyed said the Iraq War was very important to their votes. However, slightly larger numbers of voters said government corruption, scandals, and the economy were important factors. While President Bush highlighted the economy as a political strong point in the final days of the campaign, exit polls showed those who thought the issue important broke strongly in favor of the Democrats.

In the hard-fought Senate race in Virginia, Senator Allen, a Republican, faced a former Navy secretary running as a Democrat, James Webb Jr. With 99% of precincts reporting, Mr. Webb held a narrow lead, 50% to 49%, over Mr. Allen. According to the Associated Press, the two men were separated by about 2,500 votes out of nearly 2.3 million votes cast. Thousands of absentee votes were still to be counted.

A ballot measure to amend Virginia’s constitution to ban same-sex marriage passed, 58% to 42%, but it was not clear that the measure had the expected spillover benefit for Mr. Allen. Exit polls indicated nearly a third of those voting against same-sex marriage supported Mr. Webb.

In Tennessee, Rep. Harold Ford, a Democrat, trailed his Republican opponent, Robert Corker Jr., 48% to 51%, with about 88% of the precincts reporting.

In Missouri, Senator Talent, a Republican, faced a feisty challenge from a Democrat, Claire McCaskill. With about half the precincts in, Mr. Talent led, 51% to 45%. The gap was expected to narrow as still-uncounted votes from urban areas were tabulated.

A Missouri ballot measure to promote stem cell research was trailing last night 47% to 53%. The referendum prompted a public squabble between Rush Limbaugh and Michael J. Fox.

Television commentators, who gained access to the exit poll numbers at 5 p.m., offered downbeat assessments of Republican performance in the election. However, Fox News reported that, as in past years, there were signs that the exit poll results may have been skewed towards Democrats. Fox said it would not rely on the exit survey to project outcomes because Democratic candidates were running 6% to 8% better in the survey than in early returns from the same precincts.

While those exit polls suggested voters were motivated by a series of concerns, Democratic officials described the election results as a direct rebuke to Mr. Bush’s policy in Iraq.

“All Americans have acknowledged that what were doing in Iraq isn’t working and we desperately need to change course,” the chairman of the Democratic Congressional Campaign Committee, Rep. Rahm Emanuel of Illinois, told backers in Washington last night.

However, the chairman of the Democratic National Committee, Howard Dean, acknowledged that the new Congress might disappoint some voters expecting immediate action on the war. “There’s not a lot we can do to actually force the president to leave Iraq,” Dr. Dean told CNN.

According to exit polls, voters’ views on the Iraq war closely tracked political party affiliation. Only 12% of Democrats said they supported the war, while 79% of Republicans did. Among independents, about 39% said they were in favor of the war.

An independent who has been generally supportive of the Iraq War, Senator Lieberman of Connecticut, won re-election handily last night over Ned Lamont, who had defeated Mr. Lieberman in the Democratic primary. Exit polls showed Mr. Lieberman did better with Republican voters than with Democrats. Mr. Lieberman has said repeatedly that he will continue to caucus with Democrats.

Shortly after polls closed in New Jersey last night, the only Democratic incumbent in the Senate facing a strong Republican challenge, Senator Menendez, was projected as a winner over Thomas Kean Jr. Republicans also hoped for a victory in Maryland, but returns showed their candidate there, Michael Steele, coming up short against the Democrat, Rep. Benjamin Cardin.

Across the nation, there was a flurry of reports of voting site irregularities and incidents of election-related intimidation. In at least seven states, polling places were kept open late, often due to problems with voting equipment. A federal judge in Ohio ordered some Cleveland-area polling sites which were scheduled to close at 7:30 p.m. kept open until 9 p.m. because technical issues with electronic voting machines caused polling stations to open late. Some sites reverted to paper ballots.

In many states, new requirements for identification tripped up poll workers and voters, even some who live and breathe politics. Governor Sanford of South Carolina, a Republican up for reelection yesterday, forgot his voter registration card and was turned away when he tried to vote. He said he planned to obtain a duplicate and return to the polls later in the day.

Rep. Steve Chabot, a Republican of Ohio, was turned away from his polling place because the address on his driver’s license differed from his home address. He returned a short time later with a bank statement and was allowed to cast his ballot.

In New Jersey, one of Mr. Kean’s offices was padlocked shut and keys were broken off in the office’s lock. Mr. Kean’s aides blamed workers for his Democratic opponent, Mr. Menendez. His campaign denied involvement.

Automated calls to voters also triggered charges and counter-charges. In Virginia, Mr. Webb’s campaign released audio of a phone message in which a prospective voter was threatened with jail. “This is the Virginia elections commission. We’ve determined that you’re registered in New York, as well. Therefore, you will not be allowed to cast your vote on—on Tuesday. If you do show up, you will be charged criminally,” the message said.

The most bizarre incident of the day may have come in Kentucky, where a poll worker was arrested after he allegedly choked a voter who refused to mark his ballot for a judicial contest.

In California, opinion polls suggested that Governor Schwarzenegger, a Republican, would be swept back into office with a substantial win over his Democratic challenger, Phil Angelides. Mr. Schwarzenegger’s popularity suffered last year as a series of ballot measures he backed were soundly defeated. However, in recent months, Mr. Schwarzenegger’s numbers have soared as he aped Democratic positions on global warming and the minimum wage.

California was also one of 12 states considering ballot measures aimed at limiting government intrusions on private property. Sponsors of the initiatives said they were needed to counteract the Supreme Court’s ruling last year upholding broad eminent domain powers, even for projects destined for private developers. Opponents said the measures would mire local governments in litigation and make it costly or impossible to change zoning laws or enforce environment-related restrictions on land use.

In Michigan, voters were asked to decide the future of race- and gender-based affirmative action in state contracting, employment, and education.