For six tumultuous years President Bush has provoked intense opposition while mobilizing passionate support for an ambitious conservative agenda.

On Tuesday, that perilous strategy crumbled — and triggered his party's abrupt fall from power.

Republicans lost control of the House, and teetered on the edge of losing the Senate as well. The widespread losses will present Bush and the GOP with a sharpened challenge from congressional Democrats eager to command attention for their policy priorities, such as raising the national minimum wage, and to investigate the administration's performance on Iraq, global warming and other issues.

In the long run, the reversals raise fundamental questions about the viability of the strategy Bush and his chief political advisor, Karl Rove, have pursued to build a lasting Republican political majority.

Bush and Rove placed their main emphasis on unifying and energizing Republicans and right-leaning independents with an agenda that focused squarely on the goals of conservatives.

But Tuesday's broad Democratic advance underscored the risks in that approach: In many races, Republicans were overwhelmed by an energized Democratic base and a sharp turn toward the Democrats by moderate swing voters unhappy with the president's performance.

"The story line really is that the Democrats are winning the middle," said Democratic pollster Al Quinlan.

Veteran GOP pollster Bill McInturff said: "Iraq is front and center of this election, and people voted for change. The GOP base held — was motivated and voted — but the margins among independents and moderates [for Democrats] was too much to overcome."

The National Election Pool exit polls conducted by Edison Media Research and Mitofsky International showed that 80% of voters who disapproved of the Iraq war voted Democratic for Congress, while 80% who approved voted Republican. But only about two in five voters approved of the war, while nearly three-fifths disapproved, according to figures posted by CNN.

Tuesday's election may represent a bookend to the historic Republican landslide in 1994.

In that election, Republicans captured the Senate by gaining eight seats and won the House for the first time in 40 years by gaining 52 seats. The engine for the GOP advance was a widespread backlash, both among its core supporters and independent swing voters, when Democratic President Clinton veered left on several key issues after promising to govern as a centrist.

Republicans have controlled the House since then, and the Senate for all but 18 months. But on Tuesday, a political uprising that looked like the mirror image of the voter revolt against Clinton broke the GOP's grip on the House and left Democrats within reach of a Senate majority, depending on final results in Virginia and Montana.

The election saw Democrats strengthen their hold over the regions in the country where they are already strong, with Senate victories in Maryland, New York, New Jersey and Rhode Island, and House gains in Pennsylvania, Connecticut and New York.

At the same time, Democrats pushed into Republican territory with a big Senate win in Ohio, a pick up of three House seats in Indiana, as well as gains in the interior West.

The Democratic successes in such places chipped away at one of the most powerful patterns of the last few decades: a tendency for each party to consolidate its control of House and Senate seats from states it usually carries in the presidential races.

Republicans continued to enjoy strong support from their core supporters, based on the results from several key races and exit polls.

In Virginia's tight Senate race, for instance, Republican Sen. George Allen stayed nearly step-for-step with Democrat Jim Webb partly by capturing nearly 60% of the vote in Chesterfield County, a traditional GOP stronghold outside Richmond, and running slightly better than he did six years ago in Chesapeake, a conservative military-influenced community in the state's far southeast corner.

Republicans also held hotly contested GOP-leaning districts in Florida and Virginia and mounted strong challenges against Democratic House incumbents in Georgia.