Al Qaeda Still at Work in U.S., Officials Say

Kenneth Katzman, a terrorism analyst for the research arm of Congress, said the U.S. presence in Iraq also has been a boon for Al Qaeda, allowing it to "piggyback" on local Islamic political and religious movements worldwide and recruit their followers. "This is an organization that was very much off balance a year ago, but that has significantly gained ground in the past year," Katzman said.

Al Qaeda has also orchestrated recent terrorist attacks in Saudi Arabia, Morocco and perhaps even in Iraq, U.S. officials said, and has continued to infiltrate operatives into the U.S.

Just how many such operatives are in the United States is unclear, but finding them is the FBI's most pressing and urgent priority, according to Larry Mefford, the FBI's chief counter-terrorism official.

Mefford, in recent congressional testimony, said Al Qaeda remains an extremely deadly organization capable of mounting simultaneous and large-scale terrorist attacks, including within U.S. borders. In a briefing with reporters, Mefford said he believed the presence of hard-core Al Qaeda operatives in the United States is "very small but

Mefford cited the cases of Adnan El Shukrijumah and Iyman Faris, two Al Qaeda operatives who acted as Al Qaeda scouts in the United States after being sent here by Mohammed, the Al Qaeda operations chief.

Faris, an Ohio truck driver, was arrested and has pleaded guilty, but Shukrijumah remains at large and is believed to be overseas. FBI officials liken him to Sept. 11 plot leader Mohamed Atta, saying he is particularly dangerous because he is a trained pilot who is fluent in English and familiar with the United States and its customs because he lived here for years.

Captured Al Qaeda leaders such as Mohammed and Zubeida have confirmed to interrogators their long-running efforts to send waves of sleeper agents to the U.S., but so far, U.S. authorities have found little or no evidence of such operatives.

Some officials said that's because so many terrorists are new recruits who were not on their radar screen or in their databases, while others are veteran guerrilla warriors who could be using aliases or simply sneaking across borders.

"That's what people don't get. They think we know the names of all the terrorists and we don't. Sept. 11 proved that," said FBI Supervisor Special Agent Peter J. Ahearn, who heads the bureau's Buffalo, N.Y., field office near the Canadian border.

"Every time my pager goes off or my cellphone goes off, that's what I'm worried about, and we are all like that ... that it is going to be the call that we had something major go down," he said. "It's what I don't know, what the FBI doesn't know and what the CIA doesn't know is what worries us. It worries all of us."