The Senate passed the measure early this morning by a vote of 77-23, after the House approved it yesterday, 296-133.
Under the measure, Bush could attack Iraq so long as he certified to Congress in advance -- or no more than 48 hours afterward -- that diplomatic efforts had failed and that the use of force would be consistent with the war on terrorism.
The president wanted overwhelming votes in Congress as a way to show the world -- and the United Nations -- that America is unified in its willingness to disarm Hussein of his weapons of mass destruction.
"The House of Representatives has spoken clearly to the world and to the United Nations Security Council," Bush said after the vote. "The gathering threat of Iraq must be confronted fully and finally."
The House vote, though, included a thinner base of Democratic support than many had expected. Nearly two-thirds of Democrats voted against the resolution, going against their leader, Rep. Richard A. Gephardt of Missouri. In the Senate, by contrast, a majority of Democrats supported the measure.
Bush has said repeatedly that the resolution's passage does not guarantee that he will launch an attack. He has said he will do so only as a last resort, if Hussein continues to ignore demands that he disarm. Still, lawmakers cast their votes with the understanding that the resolution could lead to an open-ended war with Iraq.
"We are confronting the grave issues of war and peace," said Senate Majority Leader Tom Daschle, a South Dakota Democrat, who threw his support to the measure only this week.
"These questions go directly to who we are as a nation. How we answer them will have profound consequences -- for our nation, for our allies, for the war on terrorism, and -- perhaps most importantly -- for the men and women in our armed forces who could be called to risk their lives because of our decisions."
Senate debate stretched into the night, as members of both parties exercised their rights to be heard on a measure of historic magnitude. Broad approval was not in doubt, though, even as Democrats made several unsuccessful efforts to narrow the authority they were granting Bush.
But the wide margins of support in both chambers masked an uneasiness among many -- particularly Democrats. Some argued that in a pre-election atmosphere, after persistent calls from an administration intent on striking a hawkish stance on Iraq, Congress had too readily yielded its prerogatives and handed too much authority to the president.
"The Senate, in following this preordained course of action, will be doing a grave disservice to the nation, and to the Constitution on which it was founded."
Many opponents blamed Bush, and the pressure his administration imposed to approve a resolution before the November elections, for what they characterized as a rush to judgment on an overly sweeping authorization. They also acknowledged that the bipartisan support of congressional leaders for the resolution had made it hard for their voices to be heard.
"The leaders -- all of them, in both parties -- could have gotten us a better deal, and they didn't," said Rep. Benjamin A. Cardin, a Baltimore Democrat who voted against the resolution. "Congress made a mistake. We gave [Bush] far too much power. It becomes an historic mark against Congress in yielding too quickly to an entirely new foreign policy."
The resolution was backed in the House by 215 Republicans and 81 Democrats; opponents included 126 Democrats, one independent and six Republicans, including Rep. Constance A. Morella of Montgomery County.
Among the Maryland lawmakers, Cardin and Morella were joined in their opposition by Rep. Elijah E. Cummings, a Baltimore Democrat.