The KGB secret police contact of Sgt. Clayton J. Lonetree, the Marine accused of spying for the Soviets, was long considered a "very sharp" source by U.S. Embassy diplomats in Moscow, who never knew of the links between the two men, Lonetree's trial was told yesterday.

American diplomats met regularly with the KGB contact, and routinely passed on to Washington

information he gave them about

Soviet leaders, the court was

told.

Shaun M. Byrnes, a career Foreign Service officer who heads the embassy's internal political unit, testified that he met 22 times with a Soviet official known to him as Alexei Yefimov until he was told to sever the contact after Yefimov was revealed as Lonetree's alleged spy handler this year.

Yefimov, who used the name "Uncle Sasha" in his dealings with Lonetree, had also been a regular and valued contact of Byrnes' predecessors, Geoffrey Chapman and Kent Brown, Byrnes said.

The prosecution in Lonetree's court-martial rested its case yesterday, and defense attorneys said they will not call Lonetree to the stand to testify.

Byrnes testified that he knew Sasha only as Yefimov, "a Soviet official who claimed to work for the State Committee for Science and Technology." Yefimov is now known to be a KGB agent who recruited Lonetree when the Marine was assigned to guard the U.S. Embassy in Moscow, and who visited him at the U.S. Embassy in Vienna, his next post.

Lonetree is on trial on 13 counts of espionage, larceny and conspiracy at the Quantico Marine Base in Virginia, charged with passing sensitive material to the KGB in Moscow and Vienna while stationed with Marine Security Guard units between 1984 and 1986. If convicted he could face a life sentence.

Under cross-examination by defense counsel William M. Kunstler, Byrnes said Yefimov told him at their first meeting, in Moscow in July 1985, that he had first approached Brown in 1983 on instructions of the Soviet Central Committee and with KGB approval. The purpose of the monthly contact was to establish a communication channel between the United States and the Soviet Union, Byrnes said.

Byrnes said he had never disclosed classified information to Yefimov. But information and interpretation of Soviet internal politics provided by Yefimov was sent to Washington in classified cables, as was any political information obtained from Soviet contacts, Byrnes said.

After all Soviet nationals employed at the embassy were withdrawn by the Soviets last October, Yefimov questioned Byrnes on the morale of U.S. Embassy personel, Byrnes said.

By then, Lonetree had been reassigned from Moscow to the embassy in Vienna.

Byrnes disclosed that even before Yefimov is known to have had his first clandestine meeting with Lonetree in mid-1986, the Soviet had tried unsuccessfully to elicit information about Lonetree and his habits from Byrnes.

Yefimov asked whether Lonetree used Moscow's subway, the Metro, Byrnes testified. Byrnes said he told Yefimov he didn't know. Lonetree's relationship with a Soviet woman who introduced him to the KGB agent began with what the Marine believed to be a chance encounter on the Metro, the court heard earlier.

When Lonetree's alleged espionage activities first became public this year, Yefimov questioned Byrnes in Moscow "specifically" on whether the Marine had confessed or had been discovered by U.S. authorities. (He had confessed).

"Yefimov sought to ascertain how much I knew about the case -- and by extension, how much the U.S. government knew," Byrnes said. Yefimov asked whether Byrnes knew who Lonetree's Soviet lover was, Byrnes said.

Byrnes related to the court-martial jury of eight officers that he told Yefimov he didn't know. "Then there was a discussion about how it was possible for people to fall in love, that there might be nothing more to it than that."

In earlier hearings the court learned that Lonetree had an affair with a Soviet translator at the embassy, Violetta Sanni.

After Sasha was identified as Yefimov, Byrnes was told to challenge the Soviet about his contact with Lonetree, Byrnes said.

"I asked him if he knew Lonetree, and if he had handled him," Byrnes said.

"Yefimov did not appear shocked or surprised {at the question}. He looked me straight in the eye and said he did not know Lonetree and he had never dealt with him.

"He asked me to pass this on to the ambassador and to Washington. I thought he was lying," Byrnes said.

Yefimov told Byrnes he would "like to discuss the matter in more detail. He said he would give me a call," Byrnes said. However, when Yefimov contacted Byrnes a month later and said he would "like to talk," Byrnes told the Soviet he had been instructed to sever the relationship. "He said he understood, and we said goodbye," Byrnes said.

Byrnes, who testified for more than an hour, described Yefimov as "one of the very best, one of the sharpest Soviets I have known." Some of Byrnes' testimony was taken in closed session.

After calling CIA counterintelligence assistant director Gardner Hathaway to testify in closed court yesterday, military prosecutors closed their case after seven days of testimony.

Defense counsel Kunstler then told Judge Philip Roberts, a Navy captain, that the defense will not call any witnesses. Kunstler has complained outside of court that his attempts to call several witnesses, including some to give expert testimony on U.S. intelligence operations, had been thwarted by the judge.

The case is expected to go to the jury Friday after both sides present closing arguments.

Lonetree voluntarily revealed his KGB contacts in Vienna late last year, and in sworn statements that have been admitted into evidence, offered details of his relationship with Sanni and Sasha and the information he passed to them.