WASHINGTON — Senator Clinton, the New York Democrat whose husband authorized the bombing of Serbia without explicit congressional approval, is maneuvering to ensure that President Bush must go through Congress before launching any military action against Iran.

The senator spoke about Iran on the Senate floor yesterday after Mr. Bush backed away from a central claim of some of his commanders in Iraq, who presented evidence Sunday that they said proved Tehran is supplying insurgents in Iraq with advanced roadside mines that have claimed the lives of 170 American soldiers.

While Mrs. Clinton is not the first Democratic leader in Congress to demand prior congressional approval for any strike on Iran, her speech yesterday marks a turn for the New York lawmaker, who has reversed her hawkish approach to the wider war on Islamic terrorism as public approval for the war in Iraq has ebbed.

“It would be a mistake of historical proportion if the administration thought that the 2002 resolution authorizing force against Iraq was a blank check for the use of force against Iran without further congressional authorization,” Mrs. Clinton said. “Nor should the president think that the 2001 resolution authorizing force after the terrorist attacks of 9/11 in any way authorizes force against Iran. If the administration believes that any, any use of force against Iran is necessary, the president must come to Congress to seek that authority.”

That position is at odds with President Clinton’s unilateral decision to bomb Serb military targets beginning on March 26, 1999, when America and NATO launched a war to stop Slobodan Milosevic from cleansing the province of Kosovo of ethnic Albanians.

Twenty-six members of Congress later sued the Clinton administration on the grounds that the bombing campaign constituted a violation of the War Powers Act. Mr. Clinton’s Justice Department argued at the time that the War Powers Act not only gave the president the authority to drop the bombs on Belgrade — over two congressional votes rejecting a declaration of war on Yugoslavia — but that he was not required to seek congressional approval because Congress had appropriated the funding to launch the air offensive.

Mrs. Clinton defended the Kosovo campaign in a speech on October 10, 2002, before casting her vote to authorize the use of force in Iraq. “We and our NATO allies did not depose Mr. Milosevic, who was responsible for more than a quarter of a million people being killed in the 1990s. Instead, by stopping his aggression in Bosnia and Kosovo, and keeping on the tough sanctions, we created the conditions in which his own people threw him out and led to his being in the dock being tried for war crimes as we speak,” she said in the 2002 speech. Milosevic died in prison in the Hague in 2006.

Mr. Bush has said repeatedly over the last two weeks that he has no intention of authorizing an invasion of Iran. He has also said for more than two years that “all options are on the table” for an aerial bombardment of Iran’s centrifuge facilities.

Since January 10, however, when Mr. Bush outlined his new Iraq strategy, Democrats have worried aloud about the prospect of a new war with Iran.

Yesterday, Mr. Bush responded to the questions of a press corps who appeared skeptical about the new intelligence implicating Iran in the attacks on American soldiers. The president said he was not sure whether the top leaders in Iran were aware of the activities of the regime’s Quds Force, an elite security service that supports anti-Israel and anti-American terrorists throughout the Middle East.

“What we do know is that the Quds Force was instrumental in providing these deadly IEDs to networks inside of Iraq,” he said. “We know that. And we also know that the Quds Force is a part of the Iranian government. That’s a known. What we don’t know is whether or not the head leaders of Iran ordered the Quds Force to do what they did.”

The uncertainty about whether Quds Force activities are the same as regime activities was underscored Sunday, when the chairman of the Joint Chiefs of Staff, General Peter Pace, said he did not know whether the Iranian regime “clearly knows or is complicit” in the transfer of roadside bombs to insurgents in Iraq. That is also the view of the CIA, whose analysts have expressed skepticism internally that the supreme leader of Iran or the theocracy’s National Security Council approve the activities of the Quds Force.