By loosening the bonds on federal agents' powers, the U.S. will hopefully prevent another Sept. 11 from happening, the country's top lawmen said Sunday.

"We are at war," Attorney General John Ashcroft said on Fox News Sunday. "We have very serious challenges to address. And to leave us with agents who have their hands tied in the field so that they can't get the information that they need to get, I think, is foolhardy."

And though the government has improved vastly since last year, the job will never be complete, he said.

"I mean, we've taken dramatic steps, large steps. We're far better off than we were months ago. We'll be better off down the road," he said. "I don't know if we're ever going to dust our hands and say, 'We're through, we don't ever have to change again.' We should understand that the way to be best prepared is to always be sensitive to the changing environment in directing our resources to preventing terrorism, based on our understanding of the environment."

FBI Director Robert Mueller defended the government against criticism that it had information that could have prevented the attacks.

"I don't think it was likely," Mueller said, despite clues about the hijackings beforehand.

Mueller last week suggested that investigators might have uncovered the plot if they had been more diligent about pursuing leads before Sept. 11.

Ashcroft said he did not believe there was "a substantial likelihood" of preventing the attacks.

"My view is that the information we now have does not indicate that there was a substantial likelihood of detecting this," Ashcroft said.

Joint closed-door hearings beginning Tuesday by the House and Senate intelligence committees are intended to find out why the attacks were not foreseen by either agency.

Mueller also defended broad new powers for the FBI to monitor Americans, saying the public has higher expectations today for the government to protect them against acts of terrorism.

The Bush administration decided last week to issue new surveillance guidelines that allow the FBI to monitor Internet sites, libraries, churches and political organizations to help prevent domestic terrorism.

On NBC's Meet the Press, Mueller said, "We have to be very careful to balance" different priorities, to guard "against incursion of the freedoms that we enjoy and that we are trying to protect."

Ashcroft said it was what the public wanted.

"We have a new responsibility. The American people rightfully expect it of us. That's to prevent," the attorney general said on ABC's This Week.

But the chairman of the House Judiciary Committee believes the Justice Department "has gone too far" in relaxing rules developed under a Republican president, Gerald Ford, to bring an end to FBI excesses.

There is no need "to throw respect for civil liberties into the trash heap" in order to improve the FBI's ability to fight terrorism, Rep. James Sensenbrenner, R-Wis., said Saturday.

Intelligence committee leaders said they were not in a rush to judgment and planned a careful review on whether the attacks were preventable.

"This is serious business and we want to go on the basis of fact," said Rep. Porter Goss, R-Fla., chairman of the House committee.

The Associated Press contributed to this report.