A defense lawyer for accused spy Jerry Alfred Whitworth went on the attack today against John Anthony Walker Jr., suggesting through questions that Walker, in order to protect his family, was lying about the origin and membership of the espionage ring he headed.

In the testiest moments of two full days of cross-examination, Walker denied that his brother, retired Navy Lt. Cmdr. Arthur James Walker, had recruited him to spy for the Soviets, and that his half-brother Gary Walker, a third-class Navy petty officer, passed Navy secrets to him.

According to an FBI report, Walker's ex-wife, Barbara Joy Crowley Walker, told investigators that Arthur Walker recruited John Walker, rather than the other way around, as John Walker has testified.

John Walker called that account "a delusion from Barbara's drunkenness." Barbara Walker, who tipped the FBI off to her husband's activities, has been given immunity from prosecution and is expected to testify next week.

Walker also said that he encouraged his son, Navy Seaman Michael Lance Walker, to tell his mother that he was spying in order prevent Barbara Walker from exposing the ring.

"It was more for his Michael's safety" than for his own, Walker said.

However, he said under questioning by Larson, "Yes, I could benefit from that as well."

Walker said his ex-wife alternated between periods when "she wanted to work with me and be a good spy" and threatening to turn him in, "usually in a drunken tirade along the lines that she was going to get me."

After their 1975 divorce, he said, Barbara Walker blackmailed him "in a sense . . . when she asked for money, she knew she was going to get it."

John Walker pleaded guilty to espionage and promised to testify against Whitworth, his former best friend, in exchange for more lenient treatment for Michael Walker, who also pleaded guilty. Under the agreement, John Walker is to be sentenced to life in prison, and Michael Walker to 25 years.

Walker has testified he broached the subject of engaging in "illegal activity" with Gary Walker but that he expressed no interest. Law enforcement officials have said Gary Walker is not a suspect.

Defense lawyers appear to be trying to suggest that Walker will lie at will when it suits him. In particular, they want to show he is disposed to lie to protect his family -- and, by implication, that the government's star witness is lying for that reason about Whitworth's involvement in the case.

Michael, Arthur and Gary Walker also are on the government's list of witnesses.

Larson had John Walker read from a letter he wrote to his brother on May 26, 1985, a week after his arrest and shortly before Arthur Walker's. "I will testify that you knew nothing, which is the truth," John Walker wrote.

"That was not the truth, was it?" Larson asked. " . . . You were offering to commit perjury for your brother's sake."

"There was no reason why he [Arthur Walker] should have been arrested, no less convicted," Walker replied. "I contend that the material he sold was not classified."

Arthur Walker was convicted of espionage and sentenced to life in prison for passing the Soviets copies of two reports marked "confidential," the lowest category of classified information.

John Walker also denied that he had urged his daughter, Laura Walker Snyder, to have an abortion in order to start spying for him while she was an Army communications specialist in 1979. He said an abortion was simply one option he proposed.

Snyder joined her mother in turning in John Walker to the FBI. Walker acknowledged writing a letter after his arrest comparing his daughter to "German children in World War II who were trained to turn in their parents."

Walker also testified that he worried that Whitworth, a former Navy communications expert, was planning to double-cross him at one stage during their alleged espionage conspiracy. Walker said those fears were raised when the Soviets reported to him in February 1984 that Whitworth's photographs of messages from the USS Enterprise were "fogged" and Whitworth revealed that he had been saving copies of the messages.