President George W. Bush was set to veto a bill including a Congress-mandated Iraq withdrawal timeline within hours Tuesday, exactly four years after declaring the end of major combat operations.
White House officials said Bush would wield only his second veto in six years and make a public statement at 6:10 pm (2210 GMT), defying calls by Democratic leaders to "listen to the American people" and end the bloody war.
Sharpening a constitutional clash for control of the Iraq war, House of Representatives Speaker Nancy Pelosi and Senate Majority Leader Harry Reid formally sent the bill to the White House after weeks of fierce debate.
"With the benchmarks to hold the Iraqi government accountable, this legislation respects the wishes of the American people to end the Iraq war," Pelosi said as she signed a bill agreed by both chambers.
Reid added: "We renew our call to President Bush. There is still time to listen to the American people. There is still time to sign this bill and change course in Iraq."
The bill makes 124 billion dollars of military funding conditional on pulling most troops out of Iraq by March 2008. But Bush was determined to veto an Iraq withdrawal timeline four years after he declared the war "one victory" over terrorism on a US aircraft carrier under a giant "Mission Accomplished" banner.
Bush, pleading for patience with his unpopular decision to send more US troops to Iraq, earlier warned at the US Central Command headquarters in Florida that a hasty withdrawal would turn Iraq into "a cauldron of chaos."
"Our enemy - the enemies of freedom - love chaos. Out of that chaos they could find new safe havens," he said. "Failure in Iraq should be unacceptable to the civilised world. The risks are enormous."
But he did not directly refer to his political game of chicken with his Democratic foes, who seek to bring home most of the roughly 150,000 US troops now in Iraq starting in October. The White House expressed anger that the Democrats timed their efforts to send Bush the legislation on the anniversary of his May 1, 2003 speech.
That was when Bush strode in a flight suit aboard the USS Abraham Lincoln aircraft carrier, where he trumpeted the fall of Baghdad and declared that "major combat operations in Iraq have ended."
"The battle of Iraq is one victory in a war on terror that began on September the 11, 2001," with the attacks on New York and Washington, Bush declared, a giant "Mission Accomplished" banner hanging behind him.
When he spoke, just 139 US soldiers had been killed since the US-led invasion launched in March 2003. But more than 3,000 have died in Iraq since then, and April has been the bloodiest month of 2007 with 104 killed.
White House spokeswoman Dana Perino told reporters that the timing "is a trumped-up political stunt that is the height of cynicism and it's very disturbing."
But Pelosi said she had signed the bill and sent it to the White House at the first opportunity, as Democratic presidential hopefuls pounded Bush over his Iraq strategy.
"We are now one signature away from ending this war," Senator Barack Obama said in a statement, urging Bush to "avoid making another tragic mistake by signing the bill that will end this war and bring our troops home."
"All the photo ops in the world can't hide the truth - his disastrous mismanagement of the war has left our troops in harm's way and made Iraq a breeding ground for terrorists," said former senator John Edwards.
"When Bush vetoes the bill, Congress should send him another bill with a timetable for withdrawal and if he vetoes that one, Congress should send him another and another until we end this war and bring our troops home," he added. Senator Hillary Clinton branded Bush's 2003 speech "one of the most shameful episodes in American history."
"America is ready for a president who will respect our armed forces by properly planning for the missions we ask our troops to undertake. America is ready to end this war and when I am president, that's exactly what I'll do," she said. It was unclear what would follow the veto - Bush's only other one rejecting legislation expanding embryonic stem cell research - because Democrats lack the votes to override the president.
Bush has said he wants to work with Democrats to get much-needed monies to the US military, but has not publicly signalled that he is ready to compromise. He plans to meet top lawmakers on Wednesday.