The government's evidence against accused Soviet spy Ronald W. Pelton includes taped telephone conversations with Vitaly Yurchenko, the turnabout Soviet defector who was formerly the KGB's security officer at the Soviet Embassy in Washington, according to court papers filed today.

Documents filed by federal prosecutors said Pelton was "incidentally overheard" in a wiretapped conversation in January 1980, the same month the government alleges he went to the Soviet Embassy and began disclosing extremely sensitive information about U.S. intelligence-gathering efforts targeted at the Soviet Union. Yurchenko was then working at the embassy and did not leave until May 1980.

The documents were filed in response to a defense motion to suppress as evidence Pelton's alleged confession made to two FBI agents during five hours of talks Nov. 24 in an Annapolis hotel room. Those talks culminated in his arrest that night on espionage charges.

The papers provide new details about that confrontation, including mention of an alleged disclosure by Pelton to the Soviets of "the location" of a Soviet intelligence leak. The papers do not give the dates when Pelton's alleged conversations with Yurchenko occurred, but they say that "voice analysis" tests were among the means used to identify Pelton's voice.

The agency has previously said that information provided by Yurchenko last fall when the Soviet defected to the United States led to Pelton's arrest.

Yurchenko abruptly decided to return to the Soviet Union in early November.

Pelton, 44, was a communications specialist with the highly secret National Security Agency for 14 years. He is accused of selling intelligence information to the Soviets during a five-year period beginning in 1980, the year after he left the agency.

In the hours before Pelton's arrest, the agents confronted him with detailed information about his first visit to the Soviet Embassy, including "his disclosure to them [the Soviets] of a location where the Soviets were losing intelligence information to the United States," according to the documents.

Pelton confirmed that he had told the Soviets about that U.S. intelligence project, according to the court papers, explaining that he chose to discuss that particular project on his first meeting with the Soviets because it "involved a matter which they could readily understand without much technical discussion."

Pelton suggested to the FBI agents that he would provide a "damage assessment" of the information he sold to the Soviets in return for a guarantee of immunity, the documents show. When the agents refused to give him such a guarantee, Pelton refused to provide specific information about what he told Soviet officials, according to the papers.

"He repeatedly declined to go into detail except to say that the Soviet officials had been interested in everything he knew about . . . his former employer, the National Security Agency," said the documents. "He specifically denied transmitting any classified documents and expressed willingness to take a polygraph on that point."

Pelton is accused of telling the Soviets about projects mentioned in a highly classified technical report he wrote in 1978 while at NSA. That information, according to his indictment, was allegedly passed during long debriefing sessions at the Soviet Embassy in Vienna, Austria, in 1980 and 1983.

He refused to discuss in detail what he told the Soviets about that report, the agents said, because he said "that might 'hang' him."

"They got more out of me than I wanted to give up," Pelton allegedly told the agents of his dealings with the Soviets. Nevertheless, he said he believed the government would not be able to prosecute him because, court papers quote him as saying, "you cannot get your witness back (meaning Yurchenko) and there are no documents."

The agents said Pelton acknowledged that "his release of information to the Soviets was costly and the 'bottom line' was that it was harmful to the country." He allegedly told the agents he had acted on impulse when he made the decision to sell information to the Soviets.

During the questioning, the agents played the tapes of the alleged conversations between Pelton and Yurchenko. While Pelton denied it was his voice on the tapes, the agents told him the voice had been identified as Pelton's by "several individuals and by voice analysis tests conducted by the FBI," according to the court papers.

Defense lawyers have contended that Pelton's statements to the agents cannot be considered a "voluntary" confession because the agents used "false promises, fraud, deceit and trickery" to elicit them.

The government documents show that the FBI agents repeatedly told Pelton their superiors needed more details about what Pelton told the Soviets in weighing whether to prosecute.

The agents also told Pelton that some espionage cases are not prosecuted and that they would let their superiors know of his cooperation. If he refused to cooperate, they said, their investigation would have to include interviews with Pelton's family and associates.