Although Arthur J. Walker has been found guilty of spying for the Soviet Union, federal officials say they are continuing to investigate whether his espionage activities were more widespread than he has acknowledged.
Officials said they were pursuing leads relating to Walker in an effort to assemble further details about a purported espionage ring, which they said involved two other members of the Walker family and a retired Navy enlisted man. All the others have pleaded not guilty.
The officials acknowledged that it was highly unusual for the government to continue such an extensive background investigation on a defendant after his conviction. But the suspicion based on circumstantial evidence that Walker might have compromised Navy secrets in his military career has made it important to continue the inquiry, they said.
Walker has told the authorities that he was recruited as a spy in 1980 by his brother, John A. Walker Jr., a retired Navy chief warrant officer. He insisted to the FBI in interviews that he gave his brother only two classified documents.
But government officials and Arthur Walker`s defense lawyers said this week that the bureau had been looking into suggestions that it was Arthur who helped instigate his brother`s espionage career as much as 20 years ago.
Investigators are also examining the possibility that Arthur Walker, a retired Navy lieutenant commander, passed information to the Soviet Union while in the military, particularly the years from 1968 to 1973, when he taught antisubmarine warfare at the Atlantic Fleet Tactical School. Walker retired from the Navy in 1973 after a 20-year career.
At a five-day trial in Norfolk, Va., Walker`s defense lawyers depicted their client as a well-meaning ''sap'' hounded by his brother into passing on two relatively innocuous classified documents.
Samuel W. Meekins Jr., one of two lawyers who represented Walker, said federal officials had repeatedly told him they believed Walker played an earlier, more extensive role in an espionage operation that government officials have called the most damaging in decades.
Sources familiar with the investigation said the suspicions that Walker did not tell everything he knew about the case were prompted by his performance on a polygraph, or lie-detector, test and by statements to the FBI by other witnesses.
Meekins said there was no evidence to support any of the further allegations. He noted that no charges of conspiracy or espionage before 1980 were included in the seven-count indictment of Arthur Walker.
''innuendo'' about his client`s deeper involvement when Judge J. Calvitt Clarke holds a sentencing hearing, now scheduled for Oct. 15.
Walker was found guilty on all seven counts of espionage and related charges. He faces a potential sentence of three life terms, 40 years in jail and a $40,000 fine.
Still awaiting trial in the case are John Walker, his friend and retired Navy enlisted man Jerry A. Whitworth, and John Walker`s son, Michael, who was an enlisted man aboard the aircraft carrier Nimitz. A U.S. district judge in Baltimore ruled Thursday that John and Michael will be tried separately.
In an interview with FBI agents, Arthur Walker denied any involvement in espionage, saying, ''I am clean,'' the FBI report said.
He reviewed his military record with the agents. ''When asked which points in his career would have been of interest to the Russians, Walker advised that would have been when he served in antisubmarine warfare and the times he served as communications and operations officer,'' according to the report.