FBI agents finished searching the house, boat, airplane and offices, cars and hotel room yesterday of retired Navy warrant officer John Anthony Walker Jr., accused of spying for the Soviet Union. Navy investigators, meanwhile, detained Walker's son, Michael Lance Walker, for questioning on board the nuclear aircraft carrier U.S.S. Nimitz in Haifa, Israel.

John Walker, 47, of Norfolk, was arrested in Rockville Monday and charged with espionage after FBI agents allegedly saw him leave a paper shopping bag containing 129 classified Navy documents at a drop site near Poolesville in western Montgomery County.

The FBI said some of the documents were believed to have come from the Nimitz, on which Michael Walker, 22, is serving as a seaman.

Michael Walker is working in a clerical position in the administration office of the operations department, which coordinates the combat and communications functions of the 90,000-ton carrier, according to Navy spokesman Lt. Stephen Pietropaoli.

According to an FBI affidavit filed in federal court in Baltimore, one of the documents confiscated from Walker stated that "this delivery consists of material from 'S' and is similar to the previously supplied material . . . . His ship departed in early March and they operated extensively just prior to deployment."

The affidavit states that the Nimitz deployed in early March.

FBI spokesman Bill Baker said the bureau is attempting to assess how many others may have been involved in the alleged espionage operation and how much damage may have been done.

Baker said that although a Soviet citizen assigned to the embassy in Washington was seen at the drop area in Poolesville after Walker left, the Soviet could not be arrested because he made "no overt acts" and remained within the 25-mile radius from Washington within which Soviet nationals assigned to Washington are restricted.

Walker, who operates two detective and debugging firms in Virginia Beach, retired from the Navy in 1976 with the rank of chief warrant officer after 20 years of service.

At the time, according to an affidavit filed in federal court in Baltimore, he held a security clearance of "Top Secret Crypto," entitling him to see top secret information with special access to codes and communications information.

An FBI investigator testified at a hearing in federal court in Baltimore Monday that Walker had been providing information to the Soviets for as long as 18 years, according to Assistant U.S. Attorney Michael Schatzow.

Walker is being held without bond at the Baltimore City Jail pending a preliminary hearing next Wednesday.

Search warrants and supporting affidavits for his house, business, boat, airplane and several cars were placed under seal Monday by federal Magistrate Gilbert R. Swink in Norfolk, according to Assistant U.S. Attorney Tommy Miller. He refused to explain why the information had been sealed.

The FBI yesterday released affidavits and warrants to search Walker's room at the Ramada Inn in Rockville, a Manila envelope that fell to the floor when he was arrested, and a blue-and-silver 1985 Chevrolet AstroVan with temporary Virginia tags parked at the hotel.

According to the affidavit, Walker checked into the hotel under a false name, J.A. Johnson, and provided a nonexistent address in Portsmouth, Va.

Among the "espionage paraphernalia" the FBI expected to find, according to the warrants, were code pads, secret writing materials, ciphers and chemicals used to develop coded or secret messages.

The warrants said the searches also were expected to yield papers revealing the identities of espionage agents and foreign intelligence officers, and "financial transactions, including payments received from or made to espionage agents and foreign intelligence officers."