Tim Caruso smiled last week as he reflected on the moment a team of FBI agents showed him what they had come up with while doing surveillance near the State Department.

As head of the National Security Division at the FBI's Washington Field Office, Caruso, 52, a veteran of more than two decades at the bureau and an expert on counterintelligence and Russian affairs, oversees hundreds of agents and others responsible for fighting terrorism and espionage in Washington. And so he was more than a little intrigued when the agents approached him last summer with something important to share.

"They brought a videotape back and said, 'Hey boss, Take a look at this,' " Caruso recalled.

The surveillance tape showed a man, identified as Stanislav Borisovich Gusev--a technical expert from the Russian Foreign Intelligence Service--suspiciously lingering outside the State Department. Caruso said the videotape showed Gusev carrying out an intelligence operation, but it wasn't clear whether he was eavesdropping on the department or involved in some other type of operation.

"What do you think he is doing?" Caruso asked the agents. "We're going to find out."

And they did. After brainstorming and strategy sessions led by Caruso and the development of a plan that included careful monitoring of Gusev's movements, the feeding of disinformation to the Russians and other investigative techniques, Gusev was nabbed in early December, but only after bureau officials had the chance to learn about his methods.

To make certain that no mistake was made, it was important to catch Gusev "red-handed" outside the State Department, Caruso said. He also wanted to confiscate the recording devices in the Russian's nearby car and the equipment in his clothing that he used to activate a small listening device planted inside a piece of molding in a department conference room. The question of how the Russians managed to plant the device remains under investigation.

Those who know him well say Caruso's handling of the high-profile bugging case is emblematic of his unusually strong analytical, management and investigative skills.

"Gusev went up against the FBI's MVP in counterintelligence," FBI deputy director Thomas J. Pickard said of Caruso. "He is the best we've got."

Pickard said he sought Caruso's help to crack the unusually difficult case involving Earl E. Pitts, an FBI agent who had provided the KGB with classified information from 1987 to 1992 but then ceased his activities. He said Caruso played an instrumental role in devising the undercover strategy that succeeding in reactivating Pitts and providing the evidence needed to prosecute him.

Assistant FBI director Jimmy Carter, who heads the Washington Field Office, described Caruso as an exceptionally strong leader.

"He has really formulated a lot of methods of solving cases in a nontraditional, intellectual manner. He is a brilliant man," Carter said.

These days, Caruso said he is most proud of the teamwork in the Washington Field Office and the focused approach and sense of initiative, adopted by agents and supervisors on the front lines in the State Department case and other matters.

"People were doing the fundamentals," Caruso said. "It was very gratifying."

Caruso joined the FBI in 1978 after graduating from Manhattan College and serving in the Army for several years. He began his bureau career in Newark, and has served stints in various offices. All along he has remained captivated by the bureau's sense of mission, which he described as the search for truth and the protection of freedom. He cited his participation in the "hunt for the mole" in the Aldrich H. Ames spy case as a career highlight.

Caruso hopes the recent State Department bugging will heighten the sensitivity of other federal agencies to the threat posed by spying in Washington, a capital he characterized as a "target-rich environment." He also displayed respect for his Russian adversaries.

"It was certainly good, aggressive trade craft to get it in there," Caruso said.

And while he appears to be a straight-laced espionage maven, associates say he has a sharp wit, without being offensive, and often makes them laugh when he makes presentations. Caruso keeps a sword leaning against his office wall, a reminder that vigorous debates are encouraged provided they don't get out of hand. When he worked for the FBI in New York, Caruso kept a 2-by-4 handy for the same reason.

"Tim has a very wicked sense of humor," Carter said.

Players

Tim Caruso

Title: Special agent in charge of National Security Division, FBI Washington Field Office.

Age: 52.

Education: Bachelor's degree in business, master's in American history, Manhattan College.

Family: Married, no children.

Other Jobs: Army; investigative staff, Office of the Special Prosecutor, New York; surveys and investigations staff (on detail from FBI), House Appropriations Committee; numerous FBI positions.

Hobbies: Golf, skiing, cooking, attending theater.

CAPTION: The FBI's Tim Caruso led the team that nabbed a Russian intelligence agent who had parked near and acted suspiciously outside the State Department.