The chief defense attorney for Sgt. Clayton J. Lonetree, the first Marine to be convicted of espionage in the 210-year history of the Corps, said yesterday he expects his client to be sentenced to life imprisonment Monday by his eight-officer court-martial jury.

"He is just a symbol" for the Marine Corps, William Kunstler said yesterday. "The jury is going to expiate the Corps now."

Kunstler said Lonetree will appeal the verdict, first in the court of military review and then, if necessary, in a civilian court. The appeal is expected to take two years, during which time Lonetree will stay in the brig at the Quantico Marine Base, where he has spent seven months in solitary confinement.

The eight officers who pronounced Lonetree guilty Friday of 13 charges including espionage, conspiracy and failure to report contacts with Soviet nationals to his superiors are empowered to impose punishment ranging from dishonorable discharge from the Marine Corps to a life sentence.

Lonetree's crimes included giving blueprints of some floors of the U.S. embassies in Moscow and Vienna to an agent of the Soviet secret police, or KGB, known to him as "Uncle Sasha," while guarding those embassies between 1984 and 1986.

The 25-year-old Marine from St Paul, Minn., also identified several CIA operatives among the U.S. diplomatic corps and provided an internal telephone list of the Vienna embassy. He received a total of $3,500 from the Soviets, $1,000 of which he spent on a dress for the Soviet woman who introduced him to the KGB agent.

Sworn statements signed by Lonetree during a six-day interrogation by agents of the Naval Investigative Service (NIS) last December formed the basis of the prosecution's case and were the subject of the defense team's main objection to the charges.

Michael Stuhff, one of Lonetree's lawyers, said outside the Quantico courtroom Friday night that the defense had been prevented by the trial judge, Navy Capt. Philip Roberts, from cross-examining NIS agents in an attempt to weaken the impact of those statements.

He said Roberts had not allowed the defense to call expert witnesses who could at least have proved that the identities of CIA operatives were not the well-guarded secret that testimony indicated.

"We were handcuffed by the judge," Stuhff said. Kunstler told reporters after the verdict that Roberts had "violated his oath of office."

During the court martial at the Quantico Marine Base, prosecution lawyers Maj. David Beck and Maj. Frank Short tried to prove that Lonetree, an American Indian, was motivated by racial hatred and an admiration for the Soviet way of life and communism.

Beck called Lonetree a traitor in his closing arguments.

Stuhff and Kunstler portrayed their client as a "misguided youth" who was bent on entrapping Sasha. He was, they contended, acting as a self-appointed, free-lance double agent.

Kunstler yesterday described Lonetree as "the supreme naive innocent."

"He felt fulfilled in his fantasy world . . . . It made him feel important. He should probably not have even been in the Marines. He was too withdrawn, too socially inarticulate, too hurt by his life," Kunstler said.

"For a while he was a big man . . . but he was not a bad man. He didn't do anything so terrible."