Washington ? 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 adviser, 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 National Election Pool exit polls conducted by Edison Media Research and Mitofsky International showed that 80 percent of voters who disapproved of the Iraq war voted Democratic for Congress, while 80 percent 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.

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

Democrats also made gains among more socially conservative, economically strained swing voters, who have provided critical votes for Republicans in recent years.

John C. Green, a political scientist at the University of Akron, said the erosion Republicans faced among affluent and working-class swing voters underscored the risks of Bush’s decision to push an agenda opposed by nearly half the country on even his best days.

“The Bush people chose to put up with a very high level of conflict,” Green said. “They didn’t try to build a large consensus majority.”

Bush wasn’t on the ballot Tuesday, but he loomed as a decisive factor. Attitudes toward Bush powerfully shaped the results.

In Missouri, for instance, site of Democrat Claire McCaskill’s nail-biting win over Republican Sen. Jim Talent, the exit poll showed that almost 90 percent of those who approved of Bush’s performance backed Talent, while nearly 85 percent of those who disapproved backed McCaskill.

That was a key to McCaskill’s victory because the majority of Missouri voters disapproved of Bush’s performance.

In other states such as Ohio, Rhode Island, New Jersey and Maryland, exit polls found much more lopsided majorities than in Missouri disapproving of Bush’s performance – a trend that created large hurdles for GOP candidates.

Especially ominous for the GOP may have been the reopening of the gender gap. In 2004, Bush used security issues to narrow the traditional Democratic advantage among women.

But with surveys for months showing women especially dismayed over the course of the Iraq war, Democrats ran up decisive margins with female voters in Missouri and other states, according to the exit polls.