W By Janet Hook and Nick Anderson

ASHINGTON – A somber House on Thursday voted decisively to authorize the use of military force against Iraq, giving President Bush a bipartisan mandate and broad power to challenge an adversary who has bedeviled the United States for more than a decade.

The Senate was poised to provide its approval of the resolution following a debate that continued late Thursday.

Bush hailed the House’s 296-133 vote, a much needed victory as he attempts to build international support for a concerted effort to disarm Iraqi President Saddam Hussein of his regime’s suspected weapons of mass destruction.

“The House of Representatives has spoken clearly to the world and to the United Nations Security Council,” Bush said. “The gathering threat of Iraq must be confronted fully and finally.”

If diplomacy fails, the congressional resolution clears the way for Bush to launch a military strike in one of the most volatile regions of the world. The measure is a foreign policy milestone that could mark the beginning of a long, potentially costly new U.S. commitment in the Middle East.

With that in mind, many lawmakers expressed the hope that the resolution will make it less likely that force will actually need to be used.

“I strongly believe that our diplomacy will achieve its purpose only if the Iraqi regime knows that a sword of Damocles hangs over its head,” Rep. Tom Lantos, D-Calif., said Thursday.

But opponents warned that, by allowing Bush to launch a unilateral first strike if he chose to, the resolution represented a troubling shift away from long standing U.S. strategy of eschewing pre-emptive attacks.

The resolution gives Bush the power to use any means he determines necessary and appropriate – including military force – to respond to the perceived threat posed by Iraq.

Bush has said repeatedly that he has not yet decided whether to resort to war. If he does, the resolution requires Bush to certify to Congress, within 48 hours after the launch of a military strike, that diplomatic avenues had proved fruitless and that an attack was “consistent” with ongoing efforts to fight terrorism.

In the Senate, key lawmakers who on Thursday lined up behind the resolution included Majority Leader Tom Daschle, D-S.D., and Dianne Feinstein, D-Calif.

Although the outcome of the Senate vote was not in doubt, the debate stretched deep into the night because virtually every senator wanted to speak. A final vote was expected late Thursday or early Friday.

In a key vote that signaled a big Bush victory was at hand, the Senate early Thursday voted 75-25 to end delaying tactics and bring debate to a close. That was a defeat for impassioned critics of Bush’s Iraqi policy, who complained Congress was being buffaloed into authorizing war even before the White House has decided to prosecute one.

“I’m in my 50th year in Congress, and I never thought I would find a Senate which lacks the backbone to stand up against this stampede, this rush to war,” said Sen. Robert C. Byrd, D-W.Va. “I think we are making one horrible mistake.”

Just a month ago, as Bush pressed his case for confronting Iraq, he had faced a phalanx of such skeptics, who included members of his own party. Although he made some concessions to congressional concerns, the final resolution gave him most of the broad powers he sought. In the final House vote, only six Republicans voted against him.

Bush’s ability to sway Democrats proved more limited – 81 of the party’s House members supported the resolution, while 126 opposing it. Also voting against the measure was independent Rep. Bernie Sanders of Vermont.

It was a stronger showing of opposition than expected by anti-war Democrats, who had predicted about 100 votes for their side.

“This represents a great accomplishment for the Americans who have expressed their concern with this rush to war,” said Rep. Lloyd Doggett, D-Texas.

But Rep. Howard Berman, D-Calif., a leading Bush ally on the Iraq issue, said the overall House vote was lopsided enough to send a message of strong U.S. resolve behind Bush’s policy.

“It gives him the tools to go to the U.N. and produce a very strong inspection resolution,” said Berman.

The administration has been trying to build support for a U.N. resolution that would establish a strict new regimen of weapons inspection inside Iraq, and threaten “consequences” if Hussein refuses to comply.

The House vote also amounted to a more resounding show of support than Bush’s father received in 1991, when a Democratic controlled House authorized the Persian Gulf War, 250-183.

The Senate vote is also expected to be far more decisive than 52-47 vote for the 1991 resolution.