WASHINGTON — A Democratic presidential candidate, Senator Biden, said yesterday he would move to repeal the authority Congress gave President Bush in 2002 to send American troops into Iraq and replace it with a narrower mandate.

The chairman of the Senate Foreign Relations Committee said the legislation was based on the idea that Iraq had weapons of mass destruction and was designed to oust Iraqi leader Saddam Hussein.

“The WMDs were not there,” Mr. Biden said in prepared remarks at the Brookings Institution, a private research group. “Saddam Hussein is no longer there. The 2002 authorization is no longer relevant to the situation in Iraq.”

The Delaware senator, who voted in 2002 to authorize military intervention in Iraq, said he was working to repeal the authorization and to replace it with “a much narrower mission statement for our troops in Iraq.”

Congress should make clear the mission is to draw down America’s forces in Iraq while continuing to combat terrorists, train Iraqis, and respond to emergencies, he said.

“We should make equally clear what their mission is not: to stay in Iraq indefinitely and get mired in a savage civil war,” Mr. Biden said.

Mr. Biden long has criticized Mr. Bush’s strategy in Iraq. It is not clear whether he would be able to draw enough congressional support to succeed in his effort which also would face a Bush veto.

The three top auditors overseeing contract work in Iraq told a House committee of $10 billion in spending that was wasteful or poorly tracked.