British lawmakers on Wednesday backed Tony Blair's determination to disarm Iraq, but rebels from his own Labor Party mounted their biggest challenge to the prime minister since he came to power in 1997.

While the government carried two votes decisively, the losing dissenters made a stronger-than-expected showing, underlining the strength of opposition to war among Britons and within Blair's party.

The prime minister emphasized that the House of Commons vote was not about whether Britain should go to war against Saddam Hussein -- he said it was too soon to make such a decision.

Instead, lawmakers by a vote of 434-124 approved a government-sponsored motion which backed the prime minister's efforts to resolve the crisis through the United Nations and called on Iraq "to recognize this as its final opportunity" to disarm. Opponents included 59 Labor lawmakers.

By a tally of 393-199, legislators rejected an amendment that said "the case for military action against Iraq [is] as yet unproven." Among those supporting the measure were 122 of Labor's 410 lawmakers, making it the biggest revolt within the usually disciplined party since it took power.

In May 1999, 67 lawmakers opposed the government in what was previously the biggest Labor revolt, over plans to cut benefits for the disabled.

Foreign Secretary Jack Straw said the House of Commons would get another chance to vote on military action if the confrontation escalates, but warned that to protect the safety of British troops it might be necessary for lawmakers to have their say after hostilities begin.

So many saw Wednesday's daylong debate and votes as their last chance to weigh in.

"If the government motion is passed unamended by this house tonight, a signal will have been given that this house endorses the timetable that is now upon us, which leads I fear inexorably to war within the next three to four weeks," said Chris Smith, a former member of Blair's Cabinet and prime sponsor of the defeated anti-war amendment.

That timetable, Smith said, "appears to be determined by the decisions of the president of the United States and not by the logic of events."

Both votes showed solid support for the government, but the strength of opposition, particularly within the Labor Party, was likely to be unsettling for the prime minister.

"It is important to recognize what [the rebels] are saying, but nobody was asking them to go to war tonight," Labor Party chairman John Reid told the British Broadcasting Corp.

The British media focused on the strength of the rebellion against Blair. Some say the prime minister could be risking his job if he leads the nation to war without U.N. support.

"This is a very significant Parliamentary occasion," said Charles Kennedy, leader of the Liberal Democrat party. The number of rebels "sends a potent signal to the governments of both Britain and the United States."

The prime minister has paid a high political price at home for his staunch support of President Bush's Iraq policy, and has been struggling to convince a skeptical British public that war may be necessary. Polls show a majority of Britons oppose any war that lacks U.N. support.

Many of the lawmakers who supported the government emphasized in debate that they were not voting for war, saying they wanted U.N. backing for any use of force and hoped to see weapons inspections continue.

When Labor lawmaker Eric Martlew told Blair as much, the prime minister, referring to a U.N. resolution that Britain, the United States and Spain introduced this week, said: "That's exactly what I want. I can assure him I am working flat out to achieve it."

"We are not voting actually on the issue of war tonight, we are voting on the issue of the government's strategy," Blair said as he answered questions from lawmakers Wednesday afternoon.

"The whole issue before the international community comes down to this -- when we said last November this was a final opportunity to Saddam, when we said there had to be full unconditional and immediate compliance, did we really mean it?" Blair said.

Blair won solid support from the opposition Conservative Party.

"Sometimes it is the threat of conflict which can establish peace," Tory foreign affairs spokesman Michael Ancram said.

But Kenneth Clarke, Treasury chief in the last Conservative government, said peaceful solutions had not been exhausted.

"I cannot rid myself of doubts that the course to war we are now embarked on was actually decided on many months ago, primarily in Washington, and we've seen a fairly remorseless unfolding of events since that time."

The House of Lords, Parliament's upper chamber, also debated Iraq but did not plan a vote. Former Prime Minister Margaret Thatcher, now a member of the Lords, attended but did not speak.