U.S. counterterrorism agencies have not detected a significant Al Qaeda operational capability in the United States since the 2003 arrest of a truck driver who was in the early stages of plotting to destroy the Brooklyn Bridge.

Nevertheless, Al Qaeda's capabilities aren't clear and the group remains dangerous, the new deputy director of the National Counterterrorism Center, Kevin Brock, said in an Associated Press interview.

The uncertainty reflects the tension facing national security officials even though the country has gone four years without a domestic attack from Al Qaeda.

Brock was the FBI's special agent in charge of the Cincinnati office that investigated Iyman Faris, now serving a 20-year prison sentence for aiding and abetting terrorism and conspiracy. Faris, a Pakistani who became a U.S. citizen in 1999, was exploring whether he could ruin the Brooklyn Bridge by cutting the suspension cables.

Brock said the case showed him Al Qaeda's weakened state following the attacks of Sept. 11, 2001. Faris didn't strike Brock as someone who could carry out a sophisticated plot though he was ordered by a top Al Qaeda leader now in custody, Khalid Shaikh Mohammed, to handle complicated operations.

"Since the Iyman Faris case and other investigations, the FBI and other agencies are just not detecting an operational capability by the Al Qaeda organization in the United States of imminent significance," Brock said.

Yet he and other senior officials say now is not the time to relax.

"We have to assume that they remain a very viable and very dangerous threat," Brock said. "You almost can't define Al Qaeda just as an entity that you can put on an organizational chart. It has now expanded to an ideology that has gotten quite dangerous."

Brock presides over one of three daily teleconference calls on the latest terror threats in the U.S. and abroad. Sitting in the operations center's conference room, he and other officials from the CIA, FBI, Pentagon and elsewhere draw from more than two dozen U.S. networks and receive information on computer monitors that, with the push of a button, emerge from within a conference table.

Elsewhere, Attorney General Alberto Gonzales said in a speech Thursday that there is no alternative to constant pressure in the anti-terror effort. "We are continuing, every day, to evaluate and employ existing laws and tools that can help us in this fight," said Gonzales, as he made a case for renewing the Patriot Act.

Forty-five days after Sept. 11, Congress overwhelmingly passed the anti-terror legislation, but its reauthorization has been delayed this year by Republicans and Democrats who want to ensure there are adequate checks on investigative powers.

In 2002, then-CIA Director George Tenet publicly touted CIA-FBI successes in bringing "terrorists to justice" by grabbing them off the streets and delivering them to third countries. Called rendition, the practice is now criticized by U.S. allies, human rights groups and some policymakers.

House Intelligence Chairman Peter Hoekstra, R-Mich., said there have been hints that Al Qaeda operatives continue to work toward attacking the United States, beyond the group's public pronouncements.

"I don't believe that ... we have gotten so good at this that we are perfectly safe. I still worry about attacks on the homeland and U.S. interests overseas and believe we have significantly more work to do," he said.

Hoekstra said the focal point has moved from the United States to Iraq because the various terrorist organizations want to beat the United States there, akin to how jihadists ran the Soviets out of Afghanistan in the 1980s.

Brock doesn't believe the invasion and war in Iraq can be blamed for the threat reports that come into his center each day. "That would be too simplistic," he said. "There is too much of a diverse nature to these threats."

Had the U.S. not invaded, Brock said, terrorists would still carry out attacks. "But now they are mostly carried out in Iraq. That is where most of the people willing to commit suicide are going."

Officials have investigated whether the leader of Al Qaeda in Iraq, Abu Musab al-Zarqawi, has connections within United States. In communications intercepted by the U.S., Osama bin Laden has encouraged al-Zarqawi to look beyond Iraq.

Brock said distant links between al-Zarqawi and individuals in the U.S. do emerge and are investigated. For example, one extremist may phone another, whose number is found on a slip of paper in a third extremist's pocket.

"But there is nothing that has surfaced in the recent past that tells us that there is some imminent threat," Brock said.

He said the most worrisome attack would be one causing mass casualties — "God forbid," a weapon of mass destruction. "We have to look at this from a hierarchy of horror, and work downward," he said.