Marine Sgt. Clayton J. Lonetree's sworn statement that he passed sensitive information to Soviet KGB agents while serving as a guard at the U.S. Embassy in Moscow was admitted into evidence yesterday at his espionage court-martial.

The statement, which Lonetree's defense lawyers sought unsuccessfully to have suppressed, details his involvement with the KGB, the Soviet secret police, in Moscow and Vienna.

Although its contents were not disclosed during court yesterday at the Quantico Marine Corps base, it previously has been reported that Lonetree, an embassy guard between 1984 and 1986, has said he gave a Soviet agent known as "Sasha" a plan of the embassy's classified seventh floor, as well as photos, home telephone numbers and addresses of embassy employes, and the location of the ambassador's office.

The first Marine accused of spying in the 38 years Marines have been guarding embassies, Lonetree, of St. Paul, Minn., faces possible life imprisonment if convicted of espionage and related acts.

Much of yesterday's session was taken up with testimony by veteran agents of the Naval Investigative Service (NIS) who offered new details of their five days' intensive interrogation of Lonetree in Vienna and London last December.

NIS investigator David Moyer told the eight-man jury of Marine officers that he was contacted in London Dec. 23 by the NIS deputy director for Europe and was told Lonetree had "admitted being involved in Soviet intelligence." Moyer said he flew the next day to Vienna, where Lonetree was assigned as an embassy guard, and met him and two men referred to in the hearing as "Big John" and "Little John". "Big John" is understood to have been CIA station chief in Vienna; "Little John" is a supposed CIA agent.

Moyer, a 23-year NIS agent, said he advised Lonetree of his rights using "standard military terminology," and Lonetree indicated he did not want a lawyer and signed a waiver of his rights. During a 2 1/2-hour interrogation that night, Lonetree revealed that his "romantic involvement" with Violetta Sanni, a Russian translator at the embassy, had begun a year earlier, Moyer said.

Sanni later introduced Lonetree to Alexei G. Yefimov, a Russian known as "Uncle Sasha," whom Lonetree said he had "come to understand was a member of the KGB," Moyer said.

"In spite of this, he continued to meet with Sasha," Moyer said. "He indicated that he knew what he had done was wrong. He knew he was going to jail for that . . . . He was very upset because he had let {the Marines} down."

Lonetree's defense team contends the NIS investigation is based on an earlier, unconstitutional CIA probe of Lonetree in which the Marine was never read his rights.

The defense, seeking to show that Lonetree was attempting to be a "free-lance double agent," has built its case in part on the Marine's assertion during the Vienna interrogation that he was trying to "string along" the KGB and had given nothing of value to the Soviets. Lonetree also denied giving certain parts of the Vienna embassy floor plan to Yefimov and said he misled him about where certain offices at the embassy were located.

Moyer said Lonetree offered to "go back to Moscow" to "atone" for what he had done by locating Edward Lee Howard, a CIA agent who defected to the KGB.

Moyer said Lonetree first indicated his intention "to bring {Yefimov} over," by misleading him, but then contradicted himself, telling his interrogators he "knew it was wrong" to have given "Uncle Sasha" the names of U.S. intelligence operatives in Vienna.

The defense holds that Lonetree believed the Soviet already knew "who the CIA" agents were.

After the preliminary Vienna interrogation, Lonetree and Moyer went to London, where Lonetree spent the next four days at a Holiday Inn near Heathrow Airport, interrogated about four hours daily by two NIS agents, Moyer said. Moyer said Lonetree signed a lengthy sworn statement Dec. 29.

In other testimony, J.R. Muldowney, who had served as a Marine guard with Lonetree in Vienna, told the court Lonetree on several occasions defended "communism and facism." He said Lonetree had argued that "Hitler and Mussolini had some good ideas, they were on the right track . . . and the Soviets were continuing along those lines. "I got the distinct feeling . . . he thought the KGB was pretty neat," Muldowney said.