WASHINGTON - Creation of an independent commission to determine whether government lapses left the nation vulnerable to the Sept. 11 terrorist attacks is an idea whose time has passed - or not yet arrived.

A surge of congressional interest in the commission proposal after recent revelations of possible bungling by the FBI and CIA has subsided, relegating it to the back burner. But supporters predict that it will be revived at some point because Americans are going to demand an independent accounting of what went wrong.

Momentum for the commission proposal was broken in part by President Bush, who opposes the outside inquiry and effectively changed the subject with his prime-time televised announcement last week of an ambitious plan to create a Cabinet-level Department of Homeland Security.

The spotlight shifted again Monday with the big - critics say overblown - announcement by Attorney General John Ashcroft that U.S. authorities had arrested a would-be terrorist who, Ashcroft said, planned to detonate a radioactive "dirty bomb" in the United States.

"It sure took it off the front page," Illinois Republican Rep. Ray LaHood said of the effect of the high-profile Bush and Ashcroft announcements on the commission proposal. "I think one of the reasons Bush did things the way he did was to push a lot of this [negative] stuff off the front page."

As for the commission proposal, LaHood said, "I think that's a dead horse."

Advocates for the commission, including relatives of people killed in the attacks, say they have not given up, however.

"They can change the subject all they want, but we are not going away," said Stephen Push, of Families of September 11th, whose wife was a passenger on the hijacked airliner that was crashed into the Pentagon. "We'll be back in July and September and for as long as it takes. This is going to happen."

Push added, "We want to make sure that we learn every lesson we can from this tragedy, so that our loved ones will not have died in vain."

Working jointly, intelligence committees in the House and Senate have been gathering evidence for months on possible intelligence failures related to the Sept. 11 devastation. Early this month, they began a series of closed-door hearings and will hold their first public session before the July 4 congressional recess.

Amid reports of intelligence breakdowns, Democratic leaders in both the House and Senate issued urgent calls last month for creation of a bipartisan, blue-ribbon panel of members from outside the government that would take a broader look at policies and lapses that might have contributed to the attacks.

In March, a bill to establish such a panel sponsored by Sens. Joseph I. Lieberman, a Connecticut Democrat, and John McCain, an Arizona Republican, was approved by the Senate Government Affairs Committee.

But Majority Leader Tom Daschle said yesterday that he doesn't have enough votes to win Senate approval for the proposal and won't bring it to the floor until he does.

"I don't know how much steam there ever was" for the commission, said Daschle, a South Dakota Democrat. "We are attempting to ensure we have the votes sufficient to pass it when we take it up."

In the Republican-controlled House, Indiana Democrat Tim Roemer has taken the lead on a commission proposal that he hopes to offer as an amendment to legislation setting policy for the intelligence agencies. The bill is expected to come up for a floor vote this month.

Roemer argued that Bush's proposed Department of Homeland Security would profit from the "wisdom" of an independent outside commission that would look beyond the intelligence community to consider possible lapses by the Federal Aviation Administration, the Immigration and Naturalization Service and other agencies.

"We need to get at the facts and not go on a political witch hunt," Roemer said.

But his chances of being allowed to offer his amendment are slim because it will be resisted by the House intelligence committee's chairman, Rep. Porter J. Goss, a Florida Republican, who will lead debate on the legislation.

"I'm not saying that what we do is going to be the final word for all time, for all history," Goss said of the inquiry being conducted by the intelligence committees.

"But I am very much aware that we have a good working relationship with the White House, access to information is working well, and I don't want anything to interfere with that. The White House is not interested in this [outside] commission, hence I am not for bringing the subject up," Goss said.

Supporters of the commission proposal contend that an outside panel would be able to conduct an inquiry free of the political finger-pointing and defensiveness that critics say is likely to characterize the congressional probe.

Sen. Thad Cochran, a Mississippi Republican, said that argument might carry more weight if many of the chief advocates for the commission - including McCain, Lieberman, Daschle and House Democratic leader Richard A. Gephardt - were not potential 2004 challengers to Bush.

Cochran said Bush's homeland security department announcement had "helped bury" the commission proposal but added that lawmakers are also becoming more confident that the intelligence committees are conducting their investigation in a professional, bipartisan manner.

"I think the quality of it is beginning to be understood," he said. "That's really where the investigation ought to take place, and we're doing it."