FBI interrogation tactics used to obtain a confession from accused Soviet spy Ronald W. Pelton were attacked today by his lawyer, who told a federal jury here that FBI agents denied Pelton his night to have a lawyer present during questioning and led him to believe that his statements would not be used to prosecute him.

Under cross-examination by Pelton's attorney, one of the agents who conducted interrogation sessions last Nov. 24 acknowledged that he let Pelton believe the FBI was considering using him in counterintelligence work. However, the agent, David Faulkner, testified that the FBI had no such intention and wanted only to elicit statements from Pelton that could be used for prosecution.

Defense attorney Fred Warren Bennett has argued that the jury should disregard Pelton's confession -- the government's principal evidence in the case -- because Pelton's constitutional rights were violated during two FBI interviews that culminated in his arrest on espionage charges that night.

Pelton, who worked for 14 years at the National Security Agency before leaving in 1979, is accused of disclosing top secret U.S. intelligence-gathering activities to the Soviets between 1980 and 1985 in return for $35,000.

Pelton's former supervisor at NSA testifed earlier that Pelton had a staff job that gave him the broadest knowledge about and access to enciphered Soviet communications, as well as how NSA handled the 60 Soviet signals that were top priority.

Faulkner said the agents told Pelton that he had the right to have a lawyer present during questioning, but if Pelton chose to bring in "an outsider," his "options" would be reduced.

Asked by Bennett on the third day of the trial why he did not tell Pelton that the only options the FBI was considering for Pelton involved prosecution, Faulkner replied, "He didn't ask."

Faulkner agreed that Pelton had asked the agents repeatedly for guarantees that he would not be prosecuted if he told them what top secret NSA information he allegedly had sold to Soviet agents. But Faulkner testified that any assurances he gave Pelton were not, in fact, false promises of immunity.

When the agents tried during the interview to get Pelton to reveal what he told the Soviets about a highly sensitive NSA communications collection system, Faulkner testified that he assured Pelton he could talk freely about it. Pelton was told "his concerns for guarantees would not be violated," Faulkner said, because the FBI already knew from other sources what he had revealed about the project.

Faulkner acknowledged that admissions Pelton subsequently made about the project, referred to in court proceedings as "Project A," were being used against him.

Bennett also questioned Faulkner about the FBI's decision, after interviewing Pelton for four hours during the morning of Nov. 24, to call him back for a second interview late that evening. He argued that the FBI, which had Pelton under constant surveillance, knew Pleton and his girlfriend had purchased the drug Dilaudid that afternoon.

Faulkner said he was aware of the 4:30 p.m. drug purchase and said he had argued with his FBI superiors against bringing Pelton back for a second interview.

Also on the witness stand today was Ann Barry, Pelton's former girlfriend, who testified that Pelton told her last summer that he was "working undercover" for the U.S. government. She said that on one occasion, the couple ran out of gas while driving from Annapolis to a pizza restaurant in Virginia, where Pelton told her he was expecting to get an important phone call.

According to previous government testimony, Pelton allegedly received monthly phone calls from Soviet agents at a wall telephone at the Pizza Castle in Falls Church. Barry said that Pelton was "extremely upset" that he missed the phone call and told her: "Ann, that was our money and now we're not going to have any."

An Internal Revenue Service agent also testified today that Pelton's bank records showed that he had made cash deposits totaling $12,500 in late March 1983, two months after the government alleges he received $15,000 in cash from the Soviets.