Attorneys for accused Soviet spy Arthur James Walker filed a motion in federal court in Norfolk yesterday seeking to suppress their client's statements to the FBI, saying that agents misled Walker into believing that he would not be prosecuted if he cooperated with the government.

Sam Meekins, one of Walker's attorneys, said the 50-year-old former Navy lieutenant commander "was told that he would probably not be prosecuted and that his cooperation would certainly be beneficial in helping assure that he would not be prosecuted."

Assistant U.S. Attorney Tommy E. Miller said he had no indication that the FBI made any promises to Walker, who was the third of four Navy men charged with espionage in what federal officials describe as one of the most damaging spy cases in Navy history. "It doesn't really matter" what the agents told Walker, Miller said. " . . . That doesn't mean anything. If he's wrong, he's wrong, he should be prosecuted. That would be like me promising you that if you killed somebody, I would still let you off the hook."

Walker was indicted last month on charges of supplying his brother John, the alleged leader of a spy ring, with confidential reports on Navy ships from VSE Corp., a defense contracting firm in Chesapeake, Va., where he worked.

Meekins said that the FBI interviewed Arthur Walker on five occasions for a total of more than 35 hours, sometimes as early as 6:30 a.m., such as after the arrest of his brother John May 20.

An FBI agent has testified that Arthur Walker admitted during the interviews that he twice passed confidential documents to his brother, knowing that it would be given to "the Russians." Meekins said yesterday that "one of the reasons" his client talked was his belief that he would not be charged. He said Arthur Walker, who gave his statements without an attorney, was shocked when agents arrested him at his Virginia Beach home May 29.

Separately, a federal judge in Baltimore yesterday set an Oct. 28 trial date for John Walker and his son, Navy Seaman Michael Lance Walker, who is also charged with espionage. They are scheduled to stand trial together, although lawyers are trying to have the case divided. A California associate of John Walker has also been accused.