Sen. Rick Santorum, R-Pa., and wife Karen appear with their children in Pittsburgh to concede to Democrat Bob Casey yesterday.

AP / GENE J. PUSKAR

WASHINGTON — Borne on a wave of dissatisfaction with President Bush that swept away even such antiwar Republicans as Sen. Lincoln D. Chafee, the Democrats were poised late last night to reclaim control of the House of Representatives.

The Republican majority in the Senate hung in the balance as well, with GOP losses in Rhode Island, Ohio and Pennsylvania, and pitched battles still under way for three more GOP-held seats.

A Democratic House majority would challenge Mr. Bush on several fronts for the rest of his presidency, with investigations of the handling of the war in Iraq, a push for such priorities as a higher minimum wage, and tough opposition to his tax-cutting and free-trade policies.

While falling support for the war was a key to yesterday’s Republican gains, the potential influence of a Democratic House on war policy was less clear. Mr. Bush is still the commander in chief and Democrats are divided on whether and how quickly to insist on the withdrawal of U.S. troops from the war zone.

But yesterday’s results seem likely at a minimum to hasten a reevaluation of the Bush administration’s conduct of the war in Iraq. Exit polls in Rhode Island and other key states showed that dissatisfaction with the war was a major factor motivating voters to choose Democrats.

Six out of 10 voters surveyed in a national exit poll as they left the polls yesterday declared themselves strongly opposed to the war. Exit polls also showed that corruption was a major issue behind yesterday’s results.

By late last night, the Democrats were almost halfway to making the net gain of 15 seats they needed to seize majority control of the House for the first time since the Republican takeover of 1994. Democrats had apparently won key Republican-held seats in Kentucky, Indiana and New Hampshire, while losing none of their own.

Among the casualties were Indiana Rep. John Hostetler, one of only six House Republicans to oppose the war resolution, and New Hampshire Rep. Charlie Bass.

In the Senate, the early news for the GOP was mostly bad, with the trend embodied in former Attorney General Sheldon Whitehouse’s victory over Chafee, the Senate Republican most frequently at odds with Mr. Bush and the only one who voted against the Iraq war resolution four years ago.

Republican Senators Chafee, Rick Santorum of Pennsylvania and Mike DeWine of Ohio all lost. But Republican Bob Corker was leading for a GOP seat in a hard-fought Tennessee contest against Democratic Rep. Harold Ford Jr.

In order to claim majority control of the Senate, the Democrats appeared to need to sweep the three closely contested races for Republican-held seats in Virginia, Missouri and Montana. Results from all remained undecided late last night.

In one New England race that commanded much attention but did not change the Senate majority picture, Connecticut Sen. Joseph I. Lieberman, running as an independent, defeated Ned Lamont, the political newcomer who had defeated Lieberman in the Democratic primary by attacking his support for the war. Lieberman has promised to caucus with the Democrats.

Majority control of the House would bring new faces — including some from the Northeast — into powerful new positions. San Francisco-area Rep. Nancy Pelosi would face no opposition to become Democratic Speaker of the House. Pennsylvania Rep. John Murtha, a hawkish Democrat who made headlines late last year when he called for withdrawal of U.S. troops from Iraq, is running against Maryland Rep. Steny Hoyer for the number-two Democratic leadership job.

Rep. Barney Frank of Massachusetts is in line to be the new chairman of the House Committee on Banking, Housing and Urban Affairs. He would likely steer the panel toward more initiatives to provide low-cost housing and improve various programs for the nation’s cities.

Rhode Island Representatives Patrick J. Kennedy and James R. Langevin both foresaw advances in their committee work and priority legislation in the event of a Democratic House majority.

Kennedy predicted, for example, that he would “have a seat at the table” when Democratic legislative priorities are set for the 110th Congress, by virtue of his fundraising work for Democratic candidates around the country.

Kennedy and others have said that his top legislative priority — a mandate for equal health insurance coverage for sufferers of mental illness — stands a good chance of House passage under a Democratic majority.

Langevin said he would hope to be elected chairman of a significant subcommittee of the House Homeland Security Committee under a Democratic majority.

Some Democratic legislative initiatives seem likely to be blocked, however, if not by a continued Senate Republican majority, then by a freer use of Mr. Bush’s veto pen.

The president is especially likely to veto the kind of big spending bills that often got a pass when written by Republicans over past few years.

Immigration is one issue that holds out some hope for bipartisanship with a Democratic House because it was the GOP House majority that frustrated Mr. Bush’s effort to enact a bill that might have included at least some provision for letting illegal residents seek citizenship in the future.

Mr. Bush’s tax-cutting program, on the other hand, seemed all but doomed to stall in the new congress.