WASHINGTON — The Defense Intelligence Agency, long a home for intelligence analysis, is joining the spy vs. spy game.

DIA joins just three other military organizations authorized to carry out offensive counterintelligence operations— the Army Counterintelligence office, the Navy Criminal Investigative Serve and the Air Force office of Special Investigations.

The classified operations will be carried out by a small, tightly controlled group at sites inside the United States or outside, but only against foreigners. It's another weapon in the Pentagon's arsenal against terrorism and espionage.

"By and large these are not run to identify spies. They are run to thwart what the officer is trying to do to us, and to learn more about what they are trying to do to us," said Toby Sullivan, the director of counterintelligence in the Office of the Under Secretary of Defense for Intelligence, in a briefing Tuesday for reporters.

Steven Aftergood, intelligence policy analyst at the Federation of American Scientists in Washington, D.C., said the offensive counterintelligence operations could include planting a mole in a foreign intelligence service, passing disinformation to mislead the other side, or even disrupting enemy information systems.

"It's risky," he said. "It can also pay off enormously. In intelligence as in football, an offense can be the best defense."

Offensive counterintelligence is not a new capability but it's new to the DIA. Two years ago, the agency got permission to conduct offensive operations on a trial basis. Now it is officially sanctioned.

"There have been spies caught," Sullivan said. He declined to detail the successes, saying they are classified.

The Pentagon agency announced Aug. 3 that it had consolidated its counterintelligence and human spying operations into a single office, the Defense Counterintelligence and Human Intelligence Center. In the process it picked up the new mission of thwarting foreign intelligence agencies and terrorists attempts to gather information or carry out attacks on the U.S. military.

The new counterintelligence organization absorbs budget, personnel and mission of the six-year-old Counterintelligence Field Activity, which managed a database of potential threats to military bases, both domestic and foreign. The database known as TALON became the focus of concern about domestic spying when it was revealed in December 2005 that the system included data on antimilitary protests and other peaceful demonstrations. It included the names of people who attended peace rallies.

A 2006 Pentagon review found that as many as 260 reports in the database were improperly collected or kept there. At the time, the Pentagon said there were about 13,000 entries in the database, and that less than 2 percent either were wrongly added or were not purged later when they were determined not to involve real threats. It was shut down in September 2007.