Mr Pitts, who joined the bureau in 1983, was arrested at its training centre in Quantico, Virginia, where he had been transferred to a less sensitive post after falling under suspicion. Hours later, he was remanded in custody at a court hearing. The Justice Department said the arrest was a "major development in a significant criminal case".
According to court documents Mr Pitts, 43, passed sensitive information "related to national defence", as well as personal data about his colleagues and suggestions on how the Russians might recruit more agents from within the FBI. "Nothing was sacred to him," said Helen Fahey, the lawyer prosecuting the case. If convicted, he could face life imprisonment or, under certain circumstances, the death penalty.
In an affidavit, the FBI said he had been unmasked in a "false flag", or sting, operation by its own agents posing as Russian contacts, after the bureau had been tipped off by his original Russian recruiter, now a US resident and a co-operating witness for the FBI. Mr Pitts's active spying is said to have begun in July 1987 when he was working in New York, and continued until 1992, when he went into a "dormant capacity". Of the money he was paid, $100,000 was kept in a "reserve" account in Moscow.
The apparent unmasking of another spy came a month after the arrest of Harold Nicholson, a senior CIA instructor and a former station chief in Romania and Malaysia, on charges of passing the names of CIA officials to the Russians in exchange for $180,000.
Mr Nicholson, who spied between 1994 and 1996, is the highest CIA official to be accused of spying - more senior even than Aldrich Ames, the Soviet and Russian mole arrested in February 1994 after the most damaging penetration of US intelligence in recent times, from which a demoralised CIA is still struggling to recover. But yesterday's arrest appears unrelated to the Nicholson and Ames cases.
Given the bureau's function of tracking down spies in the US, a turncoat FBI agent is be a huge prize for the intelligence service of Russia or any other power. The last (and thus far only) FBI employee accused of espionage was Richard Miller, jailed for life in 1986 for passing information to the Soviet Union.
The Ames case, and the long failure to catch him, laid bare a history of feuding between the FBI and the CIA. The comparative speed with with Mr Nicholson was caught was proclaimed as dawn of a new era of co-operation forged by John Deutch, the outgoing CIA director, and Louis Freeh, the head of the FBI.
For Mr Freeh and the bureau, however, the arrest of Mr Pitts is the latest in a string of embarrassments, including most recently its failure to prove sabotage as the cause of the explosion of flight TWA 800 and the botched targeting of Richard Jewell as prime suspect in the Atlanta bombing.Reuse content