WASHINGTON — Armed with improved intelligence and stronger law enforcement powers, the FBI is making progress in the war on terrorism and identifying potential Al Qaeda operatives in the United States, FBI Director Robert Mueller (search) said.

The best evidence, Mueller said, is that no catastrophic terrorist attacks have occurred since those in New York and Washington on Sept. 11, 2001.

"I think we've been successful to a certain extent in disrupting Al Qaeda," Mueller said Friday before a National Press Club audience. "But that war is not over. The threats are real."

The U.S.-led removal of Al Qaeda's training camps and bases in Afghanistan was a major setback for the organization, Mueller said. Its leaders scattered, Al Qaeda (search) now has no sanctuary from which to attempt to build chemical, biological or nuclear weapons of mass destruction, he said.

"Had we not gone in, I hate to think where they would have been," Mueller said of those weapons programs.

Greater cooperation between the FBI, CIA and their foreign counterparts has also been a major factor in progress against terrorism, Mueller said. The capture of such senior leaders as Khalid Shaikh Mohammed (search) in Pakistan has added to an intelligence haul that provides a clearer picture of Al Qaeda's presence in the United States.

"Out of that, I will tell you there have been a number of pieces of information that have proved helpful," Mueller said. "Every month, I get more comfortable that we do know who we have here in this country."

Mohammed was the key contact for Iyman Faris (search), 34, an Ohio truck driver whose May 1 guilty plea to charges stemming from Al Qaeda plots was unsealed Thursday. Faris admitted participating in schemes to sabotage the Brooklyn Bridge in New York and derail trains, possibly in Washington. Mueller said the Faris arrest was "a result of our working together" with U.S. intelligence services and foreign governments.

The USA Patriot Act (search) has been another crucial part of the government's war on terror, mainly by eliminating restrictions to sharing intelligence with criminal investigators and prosecutors, Mueller said. He called the law, passed in the weeks after Sept. 11, "absolutely essential" and complained of "misperceptions" about how its powers might be misused.

Civil rights activists and others complain that the law, which greatly enhanced the powers of investigators and law enforcers, is an unconstitutional intrusion on Americans' rights.

Mueller said little doubt exists that Al Qaeda leader Usama bin Laden still lives, and the United States must continue to be vigilant for new attacks. He said the color-coded threat level system run by the Homeland Security Department (search) is vital to that effort, even if the government can't disclose the intelligence that leads to decisions to raise or lower it.

"I do believe the American people understand it as being in their best interests," he said. "It makes the environment much more difficult to undertake attacks."