Obama, an Illinois senator, and Clinton, a New York senator, focused on the nearly 4 1/2 year war in dueling speeches only a few city blocks apart in the first-in-the-nation voting state of Iowa. Senators will have a chance to vote in the coming days on whether to begin withdrawing US forces from Iraq, where the conflict has claimed more than 3,600 US lives.

"Being a leader means that you'd better do what's right and leave the politics aside because there are no do-overs on an issue as important as war," Obama said, adding that the Iraq war should never should have been authorized or waged.

Obama, then a state lawmaker in Illinois, opposed the war from the start. Clinton voted in 2002 to give President Bush the authority to launch the invasion to topple Saddam Hussein's regime, but has said she would have opposed the war if she knew then what she knows now.

"Our message to the president is clear," Clinton told a crowd of about 250. "It is time to begin ending this war not next year, not next month but today."

Throughout the campaign, the two who have raised more money than their rivals and rank high in most opinion polls have debated the nuances of their opposition to the war.

In the Senate, Clinton and Obama are both sponsoring Iraq-related amendments to the defense bill being considered this week. Two other Democrats with White House ambitions Sens. Joe Biden of Delaware and Chris Dodd of Connecticut are sponsoring proposals as well.

Clinton, along with West Virginia Sen. Robert Byrd, will introduce an amendment to repeal congressional authorization for the war. It would require President Bush to seek new authority from Congress to extend the conflict beyond Oct. 11, 2007, five years after the original permission was given.

Obama is taking the lead on amendments that would boost funding for mental health services for veterans and require better government oversight of military contractors.

Most Democrats are expected to support an amendment that would require combat troops to begin redeployment from Iraq within 120 days of enactment.

Dodd wants to take matters a step further: He will introduce an amendment that would require troops to be withdrawn immediately and end funding for all combat operations by March 31, 2008.