WASHINGTON — Headed for a confrontation with the White House and Congressional Republicans, the majority leader of the Democratic-controlled Senate called Tuesday for an independent commission to investigate government action before Sept. 11. He said such a panel was needed for "a greater degree of public scrutiny, of public involvement, of public understanding."

The majority leader, Sen. Tom Daschle of South Dakota, said he would bring legislation before the Senate soon to create the commission. His announcement followed days of warnings from senior Bush administration officials, including the vice president, that further terrorist attacks were virtually certain.

It also coincided with congressional testimony Tuesday by Kenneth Williams, the FBI agent who reported in a memorandum to the bureau last July that potential terrorists were training in American flight schools. Meeting with lawmakers in closed session, Williams said he wrote that memo after interviewing several flight students from Middle Eastern countries who expressed extreme animosity toward the United States.

As Daschle spoke, an array of administration officials fanned out across Capitol Hill in closed-door meetings trying to head off an independent commission and to respond to congressional demands for explanations about what was known before Sept. 11. Republican lawmakers stepped up their own opposition to such a commission in a day that began in measured tones but veered toward sharp partisanship as it wore on.

Daschle criticized administration "intransigence" about sharing information with Congress. He said the disclosure that Attorney General John Ashcroft and FBI director Robert Mueller III had told President Bush only in the past few weeks about Williams' warning memo was "all the more reason why we have to get to the bottom of what it was we knew and when we knew it.

"The time has come for us to do what they did after the invasion of Pearl Harbor, do what they did with the assassination of President Kennedy," the senator said of previous independent inquiries. He said a commission, which some lawmakers envision looking back years across administrations of both parties, would supplement, not replace, a joint investigation now under way by the congressional intelligence committees.

Republican congressional leaders rallied behind the White House and flatly rejected a commission. Rep. Tom DeLay, the House majority whip said at a news conference, surrounded by other GOP House members spoke out against any public airing of the nation's vulnerabilities, saying, that "our work should prevent another terrorist attack and not make Osama bin Laden's job easier."

The Texas Republican said a commission "during a time of war is ill conceived and frankly irresponsible" and he accused the Democrats of playing politics. He said, "We will not allow our president to be undermined by those who want his job."

Daschle and the House Democratic leader, Rep. Dick Gephardt of Missouri, are both considered possible presidential contenders in 2004, as is Sen. Joseph Lieberman, D-Conn., the lead sponsor of legislation that would create a 14-member commission. The bill's co-sponsor, Sen. John McCain of Arizona, ran against Bush in the Republican primaries in 2000.

As the tug of war over a commission took place in Capitol corridors, the four senior members of the intelligence committees from both parties met with Ashcroft trying to reach agreement on Justice Department cooperation with their own investigation. The lawmakers had said recently that the Justice Department, because of concerns about protecting prosecutions, had not been fully cooperative.

Late this afternoon the four lawmakers, appearing side by side, called the session valuable and said they had smoothed the way to go forward. "The information we need, we are going to get," said Rep. Porter J. Goss, R-Fla., who is chairman of the House Intelligence Committee.

The four, aware of the calls for an outside panel, appeared determined to prove that their own inquiry would be credible, thorough and unstinting. "It's very important for this investigation to have credibility," said Sen. Richard Shelby of Alabama, the ranking Republican on the Senate Intelligence Committee, "and to have credibility you have to have the cooperation of the Justice Department and all the agencies that we will be investigating during this inquiry. Anything short of that would be a travesty."

At the White House, Ari Fleischer, President Bush's press secretary, said of the congressional inquiry, "The administration is committed to working with Congress to get it done and to do it right."

With Congress set to leave at the end of this week for a weeklong Memorial Day recess, it was not clear how soon Daschle will try to push through a vote on an independent commission, or even whether he would be successful in the Senate.

Sen. Trent Lott, the minority leader, came out against such a panel Tuesday. He noted that the intelligence committees were already working and said, "I don't think a commission would serve that good a purpose now and it would be weeks, months, before it would ever produce anything."

But Daschle, saying he planned a Senate vote "reasonably quickly" said that he would, if nothing else, put lawmakers on the record. "At the very least we ought to have a good debate about whether it's important or not to do this," he said. "Let those who oppose this idea come forth and explain themselves."

With the two parties jousting over security, Senate Republicans on Tuesday demanded that the Senate turn swiftly to legislation needed to finance the military. "Our message is defense first," said Lott.

Senior congressional Democrats for their part called for more powers and authority for homeland security director Tom Ridge, swifter development of a national security strategy and more money for homeland security.

The Democrats, led by Rep. Dick Gephardt, the House minority leader, said the revelation that Ashcroft and Mueller had only recently told the president about Williams' memo about Middle Eastern men training in American flight schools showed that the current government structure was inadequate.

"I am fond of saying that Ridge needs a real job," said Rep. Jane Harman, D-Calif., who is member of the intelligence committee. "President Dwight Eisenhower once said that the right organization doesn't always guarantee success but the wrong organization guarantees failure. And I would say no organization guarantees failure," she said.

Ridge is scheduled to produce a comprehensive homeland security plan in the next few months. "People are starting to panic," Harman said. "It is unreasonable to expect individual citizens to be able to know what to do. The leadership of this country has to provide some structure and reassurance for people so they can continue to lead their daily lives."

Congressional leaders also announced Tuesday that they will hold a special session in New York City on Sept. 6 as a show of support in the wake of the terrorist attacks. The visit will not be a full congressional session but a symbolic meeting to which each state would send at least one member from its House and Senate delegation.