Lawyers for accused Soviet spy John Anthony Walker Jr. admitted today that their client left a grocery bag later found to contain classified documents at a rural Montgomery County "drop site," and then returned twice to check whether his "contact" had picked up the delivery.

The admission came during a hearing in federal court here on Walker's unsuccessful bid to bar the contents of the paper bag from being used as evidence at his trial. FBI agents have testified the bag was filled with trash, a "Dear Friend" letter from Walker to his Soviet contact, and a stack of classified documents from the USS Nimitz.

U.S. District Court Judge Alexander Harvey II, in the first of two days of hearings on motions in the case against Walker and his son, Navy Seaman Michael Lance Walker, also ruled that FBI agents had violated John Walker's constitutional rights in obtaining a statement from him shortly after his arrest. As a consequence, Harvey said, the statement, which he described as "brief and exculpatory," may not be used at Walker's trial.

Harvey granted defense motions that father and son be tried separately and said he would set a trial date for Michael Walker, who served on the Nimitz, after John Walker's trial, scheduled to start Oct. 28.

The admission about John Walker's activities in rural Poolesville on the evening of May 19, shortly before his arrest on espionage charges, cannot be used against him at his trial.

Walker's lawyers made the statement about the grocery bag -- their first acknowledgment of their client's activities that day and his connection to the bag of classified documents -- to support their argument that Walker had not abandoned the bag and retained a "reasonable expectation of privacy" in its contents.

Therefore, argued lawyer Thomas B. Mason, the government violated Walker's constitutional rights by searching the bag without a warrant, and the fruits of that search should not be admitted at his trial.

Mason said detailed instructions from Walker's contact told him to look for a delivery from the contact at the grocery bag drop site if he did not find a package waiting for him at another location. If Walker did not find the delivery at either place, he was to pick up his own package, return home to Norfolk, and try again the next Sunday, Mason said.

In denying the motion, Harvey said Walker had relinquished his right to privacy by leaving the bag "in a location where it could have been retrieved by any passer-by, as indeed it was by law enforcement agents."

"A person who would leave at such a location what had all the appearances of a bag of trash cannot be said to have retained a reasonable expectation of privacy in its contents," Harvey said.

Defense lawyers Mason and Fred Warren Bennett had more success with their bid to suppress a statement John Walker made to agents at the FBI's Baltimore office shortly after his arrest in the early morning hours of May 20.

Walker had told agents he wanted to exercise his constitutional right not to answer any questions without an attorney present, meaning agents were supposed to stop interrogating him. Agents then showed him a copy of the "Dear Friend" letter, letting Walker know they had found the bag at the drop site. Walker initially said he had no comment, but an hour later made a statement, the contents of which were not revealed today.

Harvey ruled that showing Walker the "Dear Friend" letter was the "functional equivalent of interrogation," a point conceded by proseutor Michael Schatzow. Harvey said the fact that Walker did not make the statement immediately after being shown the letter, but rather initiated a conversation with an FBI agent an hour later, did not mean he had waived his right to see a lawyer.

The statement can still be used by prosecutors to impeach Walker's credibility if he takes the stand.

Harvey did not rule on defense motions to dismiss the cases against John and Michael Walker because of prejudicial pretrial publicity and to suppress evidence gathered in wiretaps of John Walker's telephone and in searches of his safe deposit box, cars, airplane, home and other possessions.

In San Francisco, meanwhile, Judge John P. Vukasin set a new trial date of Nov. 12 for Jerry Alfred Whitworth, John Walker's Navy buddy. Whitworth, who was indicted for espionage in June, was indicted last week on additional espionage charges as well as new counts of failing to pay income taxes on $332,000 he allegedly received from John Walker in return for his role in the reputed spy ring.

A fourth man charged in the case, John Walker's brother Arthur Walker, was convicted last week of seven counts of espionage and is awaiting sentencing Oct. 15.