By a vote of 51-46, the Senate joined the House of Representatives in backing the bill that would provide about US$100 billion for the wars in Iraq and Afghanistan this year while setting a deadline to withdraw US forces from Iraq over the next 11 months.

It was the first time that the entire Congress, controlled by Democrats since January, has defied the president. Mr Bush has repeatedly said he will not accept "surrender" dates.

The president will veto this legislation," White House spokeswoman Dana Perino said. "The president is determined to win in Iraq. The bill they sent us today is mission defeated."

Democrats might arrange to deliver their bill to the White House on May 1.

Democrats, however, doubt they have two-thirds support in Congress to overturn a presidential veto. The House passed the bill on Wednesday 218-208 on a mostly partisan vote.

If there is a veto and it is not overturned, lawmakers would likely craft another bill sending money to the troops in Iraq, possibly with some watered-down conditions that Mr Bush could accept, and leave the withdrawal fight for the future.

Just two Republican senators voted for the withdrawal bill, but Democrats hope that as 2008 elections approach, more Republicans will join the push to wind down the war.