The Justice Department's (search) new anti-terrorism powers have made it possible to track, detain and in some cases, obtain sealed agreements from terror suspects that have resulted in the prevention of more terrorist attacks in the United States, Attorney General John Ashcroft (search) said Thursday.

The USA Patriot Act (search) has made it possible to increase surveillance powers, uncover the status of Al Qaeda in the United States and learn other valuable information about terror tactics and operations here and abroad, Ashcroft told the House Judiciary Committee.

 "Our ability to prevent another catastrophic attack on American soil would be more difficult if not impossible without the Patriot Act," Ashcroft said, citing examples of the information obtained from individuals questioned under the new powers.

"These individuals have provided critical intelligence about Al Qaeda and other terrorist groups, about their safehouses and training camps, their recruitment ... One individual has given us intelligence on weapons stored here in the United States. Another cooperator has identified locations in the United States being scouted or cased for potential attacks by Al Qaeda," he said.

Ashcroft held aloft what he said were copies of terrorist declarations of war against America. One quoted Nasser al-Fahd, a prominent Muslim cleric known to be sympathetic to Al Qaeda, as saying it would be permissible if a bomb killed 10 million Americans.

Ashcroft also read aloud the names of people killed in the Sept. 11 attacks as he defended the Justice Department's use so far of anti-terrorism powers.

The USA Patriot Act has led to more than 3,000 "footsoldiers of terror" being stopped, Ashcroft said. He added the United States and other cooperative nations have deprived Al Qaeda of training facilities in Afghanistan, closed off some sources of financing and arrested key operatives.

Despite the successes, Ashcroft said Al Qaeda remains a threat.

"Let me be clear: Al Qaeda is diminished but not destroyed. Defeat after defeat has made the terrorists desperate to strike again," he said.

The USA Patriot Act, passed by Congress in the weeks after the Sept. 11 attacks, grants the government broad powers to use wiretaps, electronic and computer eavesdropping and searches, and the authority to access a wide range of financial and other information in its investigations.

Critics of the act have claimed since its inception that it denies U.S. residents civil liberties. House Judiciary Committee Chairman James Sensenbrenner, R-Wis., has said he is sensitive to those concerns, and complained earlier this year that his panel hasn't been given enough information from the Justice Department to determine whether those concerns have validity.

"To my mind, the purpose of the Patriot Act is to secure our liberties and not undermine them," he said.

Added Rep. Howard Berman, D-Calif.: "Some of us find that the collateral damage is greater than it needs to be in the conduct of this war."

Critics of the act claim to be vindicated by a Department of Justice inspector general report released Monday that said some of the 762 immigrants detained in the 11 months following Sept. 11 were denied quick access to notice of their charges — primarily visa violations — and faced harsh living conditions beyond the 90-day time period in which they can be held.

Ashcroft responded that the detentions were all lawful and carried out in an atmosphere of deep national anxiety. Of the cases, 505 individuals have been deported, one — Zacarias Moussaoui — is facing terror-related charges. Ashcroft said another 15 people have been offered criminal plea agreements, many under seal.

He added that the Justice Department will investigate remaining allegations of abuse of the detainees, although 14 of 18 cases referred so far already have been cleared without any charges being filed.

"We do not stand for abuse," Ashcroft said.

Ashcroft said he is not seeking additional powers to the Patriot Act, but is looking for some fixes to the law's weaknesses, which could be used to cause additional harm.

He also is seeking support for renewing the act after it sunsets in April 2005.

"The law has several weaknesses which terrorists could exploit, undermining our defenses," Ashcroft said, pointing to indefinite detention periods for terror suspects and longer prison terms for those who are convicted of committing terrorists acts. 

"In criminal cases where public safety is a concern such as drug dealing, organized crime and gun crimes, defendants in federal crimes are presumptively denied pretrial release," Ashcroft said. "It seems as though the crime of terrorism should have the same presumption."

Ashcroft said another fix would be to charge as "material supporters" anyone caught providing aid or working with terrorist groups.

Sensenbrenner said his "support for this legislation is neither perpetual or unconditional."

Fox News' Major Garrett and the Associated Press contributed to this report