In only the second veto of his presidency, Mr. Bush rejected legislation pushed by Democratic leaders that would require the first U.S. combat troops to be withdrawn from Iraq by Oct. 1 with a goal of a complete pullout six months later.
"This is a prescription for chaos and confusion and we must not impose it on our troops," Bush said in a nationally broadcast statement from the White House. He said the bill would "mandate a rigid and artificial deadline" for troop pullouts, and "it makes no sense to tell the enemy when you plan to start withdrawing."
Democrats made a last-minute plea for Mr. Bush to sign the bill, knowing their request would be ignored. "The president has put our troops in the middle of a civil war," said Senate Majority Leader Harry Reid. "Reality on the ground proves what we all know: A change of course is needed."
House Speaker Nancy Pelosi said the legislation "respects the wishes of the American people to end the Iraq war."
A Senate Democrat says they've pushed their demand for troop deadlines as far as they can, reports CBS News chief White House correspondent Jim Axelrod. Democrats know they don't have the two-thirds majority needed to override the veto.
Lacking the votes to override the president, Democratic leaders quietly considered what might be included or kept out of their next version of the $124 billion spending bill. Mr. Bush will meet with congressional leaders — Democrats and Republicans alike — on Wednesday to discuss a new bill.
Mr. Bush said Democrats had made a political statement by passing anti-war legislation. "They've sent their message, and now it's time to put politics behind us and support our troops with the funds," the president said.
He said the need to act is urgent because without a war-funding bill, the armed forces will have to consider cutting back on buying or repairing equipment.
"Our troops and their families deserve better, and their elected leaders can do better," Mr. Bush said.
He vetoed the bill immediately upon his return to the White House from a visit to MacDill Air Force Base in Tampa, Fla., the headquarters of U.S. Central Command, which oversees military operations in the Middle East, including Iraq.
Earlier on Tuesday, Democratic congressional leaders sent Mr. Bush legislation setting timetables for U.S. troop withdrawals from Iraq. The move came on the fourth anniversary of Mr. Bush's "Mission Accomplished" speech on the war.
The Democratic leaders staged a special ceremony to send the legislation — already approved by both the House and Senate — on its way to the White House.
On Wednesday, Mr. Bush is to meet at the White House with congressional leaders from both parties, including Reid, D-Nev., and Pelosi, D-Calif., to begin discussing follow-up spending legislation.
"This legislation honors the sacrifice of our men and women in uniform," Pelosi said at the ceremony in the Capitol. She said that provisions of the measure respect "the wishes of the American people to end the Iraq war."
Said Reid: "After more than four years of a failed policy, it's time for Iraq to take responsibility for its own future. Today, right now, we renew our call to President Bush: There is still time to listen. There is still time to sign this bill and change course in Iraq."
Some Republicans say they would support tying benchmarks to the more than $5 billion provided to Iraq in foreign aid, but nothing that would tie the hands of military commanders. It's not clear whether the White House is open to this approach, either. Secretary of State Condoleezza Rice said over the weekend that Mr. Bush would not sign a bill containing any penalties for the Iraqi government.
"House Republicans will oppose any bill that includes provisions that undermine our troops and their mission, whether it's benchmarks for failure, arbitrary readiness standards or a timetable for American surrender," said Minority Leader John Boehner, R-Ohio.