WASHINGTON - In a breakthrough for the White House, key Republicans and Democrats agreed with President Bush yesterday on a measure authorizing him to use force against Iraq. The agreement sets the stage for Congress' approval of a war resolution as early as next week.

The compromise - the product of negotiations by the White House and bipartisan House and Senate leaders - won broad backing. It would allow Bush to invade Iraq, provided he declared to Congress that further diplomacy was useless and that an attack would not hinder the war on terrorism.

Leaders on both sides of the Capitol predicted that the proposal would win congressional approval.

"The statement of support from the Congress will show to friend and enemy alike the resolve of the United States," Bush said yesterday, flanked by Republicans and Democrats in the White House Rose Garden.

"Saddam [Hussein] must disarm, period. If he persists in his defiance, the use of force may become unavoidable," the president said of the Iraqi leader.

Emboldened by the rising support in Congress, the administration is also preparing to take a harder line with other permanent members of the United Nations Security Council in pushing for a new U.N. resolution against Iraq.

After a month of contentious debate on Capitol Hill about U.S. policy on Iraq, including wrangling over the language for a congressional resolution, House Democratic leaders and rank-and-file members of both parties fell in line behind the president's position.

"Iraq's use and continuing development of weapons of mass destruction, combined with efforts of terrorists to acquire such weapons, pose a unique and dangerous threat to our national security," said Democratic Rep. Richard A. Gephardt, the minority leader in the Republican-led House, who stood beside Bush. "We need to deal with this threat diplomatically if we can, militarily if we must."

Some senators, including Majority Leader Tom Daschle, a South Dakota Democrat, said they remain opposed to such a broad grant of authority for Bush to wage war. But they conceded that they had little chance - given the backing of House Democratic leaders - to prevail with an alternative measure.

"The honest answer is, it's probably too late," said Sen. Joseph R. Biden Jr., the Delaware Democrat who is chairman of the Foreign Relations Committee.

Biden has been pushing a more limited resolution, along with the ranking Republican on his committee, Sen. Richard G. Lugar of Indiana. But he predicted that the House would pass the Bush compromise by a wide margin. And he seemed to concede that the Senate would follow suit.

"I'm a realist," Biden said.

Daschle not on hand

Conspicuously absent from the Rose Garden yesterday was Daschle, who broke with Gephardt and declined to endorse the resolution.

Daschle conceded that the measure agreed to yesterday includes "improvements" that White House negotiators have made during the past two weeks. But Daschle and a group of Senate Democrats and Republicans seek further changes.

"The final resolution should include greater emphasis on eliminating Iraq's weapons of mass destruction, a stronger statement that operations against Iraq will not undermine the ongoing international effort against al-Qaida, and a clearer assessment of the administration's plan for the political and economic reconstruction of a post-Saddam Iraq," Daschle said in a statement.

The Senate is expected today to begin floor debate on Iraq, while the House International Relations Committee works on the compromise measure.

A small group of protesters was escorted from the International Relations Committee room yesterday after interrupting the session with shouts of "Americans do not want this war!" and "We ask you please to not go to war - the American people don't want it!"

Some House Democrats are likely to try to alter the resolution today through amendments. But Rep. Henry J. Hyde, the Illinois Republican who is chairman of the International Relations Committee, said he would try to preserve the White House language.