The House voted by 223 votes to 201 to pass the measure, in defiance of President George W. Bush, who has already vetoed a previous troop withdrawal timeline framed by the Democratic Party, and has pledged to do so again.

Four Republicans voted in favour of the plan, while 10 members of the majority Democratic Party voted against, on a day a new US government report offered a bleak snapshot of progress in Iraq.

House Democratic leaders argued during a day-long debate on the measure that Bush's war plan had failed and it was time to change tack.

"Let's change our strategy, and demand that the Iraqis step up and be responsible for their country, let's responsibly redeploy our troops," said Democratic House majority leader Steny Hoyer.

But Republicans accused their foes of backing a plan for defeat in Iraq.

House Minority leader John Boehner branded the measure a "meaningless bill that undermines our troops."

"If we fail in Iraq we know what happens, we make America less safe," he said.

Meanwhile, President George W Bush insisted the Iraq war could still be won and dismissed mounting calls for a change in strategy as US lawmakers voted again for troop withdrawals.

Bush struck a defiant tone Thursday, insisting on his authority to run the war despite a report from his administration showing the Iraqi government was making only paltry progress and growing anxiety over the war from fellow Republicans.

"I believe we can succeed in Iraq, and I know we must," Bush said at a news conference dominated by the unpopular war, which has now killed 3,612 US troops.

Bush frequently invoked al-Qaeda, warning the withdrawal of 160,000 US troops in the country would mean "surrendering the future of Iraq to al-Qaeda."

The House of Representatives answered Bush with a vote to withdraw most combat troops by April, as Democratic leaders said the president's strategy deploying an additional 30,000 troops had proven a failure.

The House voted by 223 votes to 201 to pass the measure, but the Republican coalition stayed intact: only four party members voted with the Democrats.

The troop withdrawal deadlines have almost no chance of becoming law as the Democrats are well short of the two-thirds majority needed to override a Bush veto.

But Democratic leaders see votes for troop withdrawals as a way of keeping up pressure on the president and his Republican allies.

"The president hasn't seen the last of these votes," said Jim Manley, spokesman for Senate Majority Leader Harry Reid. "We'll look forward to additional votes in September."

Bush reiterated that he is not ready to consider a change of course until the commander of US forces in Iraq, General David Petraeus, issues his assessment of the troop "surge" strategy in September.

The embattled president accused his Democratic foes of trying to encroach on his legal authority as commander-in-chief.

"I don't think Congress ought to be running the war," he said.

In a concession to lawmakers demanding more regional diplomacy, Bush said he would send Secretary of State Condoleezza Rice and Secretary of Defence Robert Gates to the Middle East in August to consult US allies on the conflict.

Both cabinet heavy hitters had postponed foreign trips to launch an intense lobbying effort of wavering lawmakers, after several key Republican senators broke with Bush in recent weeks.

The political combat came amid more violence in Iraq, where US forces clashed with Shia militants in Baghdad on Thursday in a battle that claimed the lives of two Iraqis working for the international news agency Reuters.