On Sept. 12, 2001, FBI Director Robert S. Mueller gathered the troops.

"I'll never forget it," said Ken McCabe, former head of the FBI in Pittsburgh. "He was leaning on a table, one finger pointing, and said, 'We can never let this happen again.' "

The agency's mission had just changed, he said, from being reactive to proactive -- stopping another attack at all costs.

Since that day, the FBI has devoted unprecedented resources to foiling terrorism, working with police and intelligence agencies around the world to disrupt plots like the one uncovered in England last week.

But as a result, the agency -- which enforces some 300 criminal statutes -- has cut back substantially on pursuing bank robbers, fugitives, drug dealers and other traditional criminals, leaving them to other law enforcement.

Counter-intelligence has always been a priority at the FBI, but it's now consuming so much time and manpower that the agency has de-emphasized some of its crime-fighting roles in some offices.

Like busting bank robbers.

Bank heists are part of the agency's lore. In Hogan's Alley, the fake town where agents are trained in Quantico, Va., recruits still train to handle mock bank robberies. The town even contains a replica of the Biograph Theater named for the Chicago movie house where the FBI tracked down bank robber John Dillinger in 1934.

But the FBI now lets police pursue many bank jobs. In Pittsburgh, city police handle most of them; the FBI still goes out on county cases.

The FBI has also pulled agents from various task forces combatting guns and drugs, stopped hunting fugitives and pulled many of its top agents from crime-fighting to its terrorism task forces, which include local police officers and other federal agents.

Congress has also provided money for the FBI to hire hundreds of intelligence analysts whose job is to "connect the dots" by sharing information with the CIA, National Security Agency and the rest of the intelligence community.

There has been some concern that garden-variety criminals might take advantage of all this distraction and that Congress should allocate a separate budget for terrorism within the FBI.

Crime tends to be cyclical -- what goes around comes around, said Edward Turzanski, a political analyst and intelligence expert at La Salle University in Philadelphia. "What tends to happen, invariably, is that old problems resurface."

But he also said the FBI has always been fluid, shifting its resources to meet the needs of the day.

La Roche College Professor Lawrence Likar, a former supervisor in the Pittsburgh FBI office, said the agency retooled to deal with German espionage in World War II, civil rights violations in the 1960s and Soviet spies during the Cold War.

He said much of agents' time was inevitably wasted tracking down bad leads in such major initiatives, but there were successes, too.

"When you look at every major incident in the history of the country, the FBI has been smack in the middle of that," he said.

This time it's terrorism -- and other agencies have to pick up the slack.

"When this [shift] was done, Mueller met with the heads of all the other agencies," said Mr. McCabe. "He said we're pulling out of DEA task forces, out of ATF task forces, out of the marshals' task forces. And you guys are going to have to step up."

The FBI still devotes many of its 12,500 agents to organized crime, white-collar crime, narcotics and public corruption.

And many of those investigations overlap with counter-terrorism, particularly in the way terror networks are funded through money-laundering, credit card fraud and narcotics trafficking.

"We're seeing a nexus of terrorism and the drug trade working together," said Professor Turzanski. "They do have a common cause. Terrorists very often resort to various forms of financial fraud."

Jeff Killeen, spokesman for the Pittsburgh office, said the agency is able to fight terrorism and still pursue other crimes.

The busiest unit in this region these days is the one no one knows anything about: the Joint Terrorism Task Force, headquartered at the Pittsburgh FBI office with squads in Erie and West Virginia.

Every day its cadre of police officers, analysts and agents coordinate with their counterparts in each of the FBI's 56 field offices.

"There's work to do here, there's work to do everywhere," said Agent Killeen. "The stakes are too high. I think there's a lot of tension. Stress levels are high. No one wants to be wrong."

Especially since the FBI took much of the blame for 9/11 after it was revealed that field agents knew the hijackers were up to something but couldn't get the brass to authorize an investigation.

"That's why they feel the pressure not to get things wrong," said Professor Turzanski. "The FBI had a self-image, largely well-earned, of being the pre-eminent law enforcement entity in the world. It goes beyond pride. It's real defensiveness."

The nature of the job has changed from indictments and convictions to probing and watching -- with no measurable results to gauge performance.

That can be demoralizing for some agents.

The work of the Joint Terrorism Task Force is classified. But chasing down leads, many of them bogus, is obviously a big part of the job now just as it was immediately after 9/11.

"You can't let leads go," said Mr. McCabe.

Some threats are more concrete.

Page 59 of the 911 Commission report, for example, contains a specific mention of Pittsburgh in connection with Osama bin Laden's terror network:

"A Muslim organization called al Khifa had numerous branch offices, the largest of which was in the Farouq mosque in Brooklyn. In the mid-1980s, it had been set up as one of the first outposts of Azzam and bin Laden's MAK. Other cities with branches of al Khifa included Atlanta, Boston, Chicago, Pittsburgh and Tucson."

The report goes on to say that al Khifa recruited American Muslims to fight in Afghanistan and that some of them participated in al-Qaida terror attacks, including the 1998 attacks on U.S. embassies in Africa.

Al Khifa is no longer functioning here.