Senate majority leader Harry Reid said yesterday that, although the withdrawal date would be non-binding, the bill would signal a determination within Congress to pressurise President George Bush into ending the war.
"The president has had a long time to dig the ditch we're in, but we're working very hard every day to dig out of that ditch," Mr Reid said.
Mr Bush yesterday repeated his threat to veto any bill that links funding the war in Iraq to a timetable for withdrawal, rejecting what he described as an attempt by Congress to "micromanage" the war.
"I believe strongly that politicians in Washington shouldn't be telling generals how to do their job. And I believe artificial timetables of withdrawal would be a mistake.
"An artificial timetable of withdrawal would say to an enemy, 'just wait them out'; it would say to the Iraqis, 'don't do hard things necessary to achieve our objectives', and it would be discouraging for our troops. And therefore I will strongly reject an artificial timetable withdrawal and/or Washington politicians trying to tell those who wear the uniform how to do their job," he said.
Speaking after a meeting at the Oval Office with Gen David Petraeus, the top US commander in Iraq, Mr Bush said that his decision to send more troops to Iraq had already borne fruit.
"There've been some horrific bombings, of course. There's also a decline in sectarian violence," he said.
If Mr Bush vetoes the war spending bill, Democrats need a two-thirds majority to overturn his decision and they are currently well short of that number. Mr Reid said yesterday that, if Mr Bush does not like the bill he receives from Congress, he should come up with an alternative that would unite Democrats and Republicans.
"If the president disagrees, let him come to us with an alternative. Instead of sending us back to square one with a veto, some tough talk and nothing more, let him come to the table in the spirit of bipartisanship that Americans demand and deserve," Mr Reid said.
Mr Reid said that in addition to the timetable for withdrawal, the new legislation would establish standards for the Iraqi government to meet for making progress on security and political reconciliation and would launch diplomatic, economic and political policy changes. He urged anti-war Democrats to be patient, asserting that Congress had limited room for manoeuvre on the issue.
"I understand the restlessness that some feel. Many who voted for change in November anticipated dramatic and immediate results in January. But like it or not, George W Bush is still the commander in chief - and this is his war," Mr Reid said.