WASHINGTON - As a Senate committee heard secret testimony yesterday from CIA Director George J. Tenet about discredited evidence of Iraq's efforts to buy nuclear material, the Senate rejected Democrats' calls for an independent panel to investigate the information President Bush and his aides used to justify invading Iraq.

The Democrats' effort came during debate on a $369 billion defense spending bill for 2004. Pentagon funding generally speeds through Congress, especially when U.S. troops are engaged in conflicts abroad. But this week, the bill has become a vehicle for Democrats to attack Bush administration policy in Iraq and to question the intelligence information used to build support for going to war.

The Senate voted 51-45, strictly along party lines, to reject an amendment that would have created a 12-member commission, chosen by Republican and Democratic leaders, to scrutinize assertions Bush and his top aides made about Iraq in the months before the war.

The action came as the Senate Select Committee on Intelligence grilled Tenet in a closed hearing about his role in allowing discredited evidence of Iraq's attempts to develop nuclear weapons to be noted in Bush's State of the Union address. In the January speech, Bush asserted, based on British reports, that Iraq tried to buy uranium from Africa for use in building nuclear weapons - a claim the CIA had said was unsubstantiated.

Last week, Tenet took responsibility for its inclusion and said it was a mistake.

Emerging from the session yesterday, leaders of the committee, which has been investigating pre-war intelligence on Iraq, said their inquiry would go beyond Tenet's role.

"I think there are others in the administration that knew something about this," said Sen. John D. Rockefeller IV of West Virginia, the committee's senior Democrat. "Responsibility has to be taken by a lot more than George Tenet."

Sen. Pat Roberts of Kansas, the intelligence panel's Republican chairman, said: "The director was very contrite. He was very candid. He was very forthcoming. And he accepted full responsibility. ... I think there were mistakes made all up and along the chain."

Republicans railed against the proposal for an independent commission, calling it an effort to besmirch the credibility of the Bush administration.

"I'm tired of making a mountain out of a molehill on this," said Sen. Ted Stevens, the Alaska Republican who chairs the Appropriations Committee. "This is not Watergate. This is an ongoing operation, and this is an attempt to smear the president of the United States."

Senators questioned Tenet about how the assertion in Bush's speech - 16 words that have sparked a furor on Capitol Hill - was included even after the CIA had expressed doubts about the information.

"Obviously, something broke down between the White House and the CIA or the National Security Council and the CIA," said Sen. Olympia J. Snowe, a Maine Republican on the intelligence panel. "Something went terribly wrong."

Among the things she wanted to know, Snowe said, was: "Who weighed into this process that put the president and this country in this position?"

As Democrats attacked Bush's Iraq policy and committee members grilled his top intelligence official, two Democratic presidential hopefuls - former Gov. Howard Dean of Vermont and Sen. Joseph I. Lieberman of Connecticut - called for Tenet's resignation.

Two other Democratic candidates - Sens. Bob Graham of Florida and John Edwards of North Carolina - sought instead to shift the focus to Bush.

"George Tenet has accepted his responsibility, and that's good, but at the end of the day the president, when he speaks, has to take responsibility for what he says," Edwards said. "The responsibility is not the CIA's. It's not anyone else's. It is the president's responsibility."

The White House and congressional Republicans are playing down the uranium issue as an overblown reaction to a brief sentence that they acknowledge should not have been uttered by Bush. They pointed to what they said is substantial evidence collected by Republican and Democratic administrations that Iraqi dictator Saddam Hussein possessed weapons of mass destruction.

But Sen. Carl Levin of Michigan, the senior Democrat on the Armed Services Committee, suggested that top Bush administration officials had deliberately misled lawmakers and the public with the uranium claim.

The wording of Bush's statement - saying "the British government has learned" that Iraq tried to buy uranium from Africa - was a deceptive attempt "to find a formula which they can say is technically accurate" to convince the public that Hussein was a threat, Levin said.

"Who in the National Security Council was pressuring Tenet to create a formula which created a false impression?" Levin asked.