Soviet Maj. Gen. Vasiliy I. Chitov, expelled from the United States Thursday for spying, was caught in a trap laid for him by the FBI, sources said yesterday.

Chitov, military attache at the Soviet Embassy here, was apprehended last weekend after he picked up documents that U.S. counterintelligence officers laid out as bait, the sources said. FBI agents captured Chitov after a car chase through the Northern Virginia suburbs.

Sources said the agents were surprised when they realized they had caught Chitov, highest-ranking military officer at the embassy and a member of the Soviet military intelligence agency GRU, rather than a lower-ranking officer.

Chitov, who is about 50, was living in the Skyline Towers complex in the Baileys Crossroads area of Fairfax County before his capture, according to an embassy official.

Exact details of the "sting" operation could not be learned. But sources said that no American citizen will be charged with passing classified documents to the Soviets. Government spokesmen would not comment yesterday about the operation or the nature of the documents used.

One said an investigation of a possible leak may be started because high administration officials had decided not to publicize Chitov's expulsion and now fear that the Soviet Union will expel an American diplomat from Moscow in retaliation.

FBI Director William H. Webster said in a recent interview that he is concerned about the growth of communist bloc diplomatic delegations in the United States. But he said he is hesitant about recommending cutbacks in such growth because the FBI has recruited as double agents some Soviet diplomats who might be forced to leave.

"We have recruitments in place. They took a long time to develop, and we might find they're the ones that we lose in a cutback ," Webster said. An FBI spokesman said later that Webster has discussed publicly the FBI's success in turning Soviet diplomats into double agents.

A U.S. intelligence officer said yesterday that Webster might have mentioned such recruitment in an effort to spread paranoia in Soviet intelligence ranks here. U.S. intelligence officials estimate that about 250 of approximately 600 Soviet diplomatic personnel in the Washington area are involved in gathering intelligence.

Webster noted during the luncheon interview with Washington Post editors and reporters that his counterintelligence budget has been increased to meet the communist bloc espionage threat. But he added that he still does not have enough agents for adequate surveillance of suspected foreign spies.

Last spring, the FBI added 15 agents to the 100-man counterintelligence unit at its Washington field office, sources said.

The only official government confirmation of the Chitov incident came Thursday night from a State Department spokesman, who said the general "was declared persona non grata for activities inconsistent with his diplomatic status." Chitov and his wife left the United States Thursday.

The operation that caught Chitov seems similar to one used by U.S. intelligence agencies in 1978 when a Navy commander with access to antisubmarine warfare documents lured Soviet U.N. employes into a net.

Two of the Soviets were convicted and sentenced to 50-year prison terms. The third was attached to the Soviet U.N. mission and, like Chitov, had diplomatic immunity. He was expelled.