The FBI plans to arrest more Americans on charges of spying for the Soviet Union following the arrest earlier this week of a retired Navy communications specialist and his son, a seaman aboard the U.S.S. Nimitz, bureau officials said yesterday.

"We think the ring is bigger than the two now charged," Assistant FBI Director Bill Baker told the Associated Press. "I would expect more charges against more people -- associates of the father."

There were reports last night that the Soviet diplomat involved in the case has been called home by his country rather than await certain expulsion by the United States.

CBS reported that the unnamed diplomat, who was seen near a site in rural western Montgomery County where John Anthony Walker Jr. allegedly left a shopping bag containing classified documents Monday, has been recalled by Moscow.

State Department sources said last night that the diplomat may have already left the United States.

Recall or expulsion is the normal practice in such cases because officials with diplomatic immunity cannot be charged with offenses in this country.

Walker, 47, a Norfolk private detective who is a retired Navy chief warrant officer, and his son, Michael Lance Walker, 22, who works as a communications specialist on the Nimitz, were arrested after the FBI recovered the shopping bag, which agents said contained 129 classified Navy documents.

Baker said that "based on the duration of the espionage and the access of those who have been charged, you have to assume the damage they caused is substantial." An FBI agent in federal court in Baltimore earlier this week that the spying may have been going on for as long as 18 years.

Officials said a search of a Manila envelope that fell to the floor when John Walker pulled a handgun on FBI agents who arrested him early Monday at a Holiday Inn in Rockville contained what bureau spokesman Lane Bonner termed "very detailed, very precise" instructions in English from Soviet agents on how to leave and remove information from clandestine drop sites.

The envelope also contained maps of apparent Soviet drop sites in the Washington area, and photographs, according to FBI officials.

An inventory of the contents of the envelope filed in federal court in Baltimore lists a map of Montgomery County, two instruction sheets -- one ending with the words, "picked up my delivery" -- and 14 photographs.

Baker said that the FBI was searching for bank accounts and other assets held by John Walker because "we believe the father's reason for doing this was for financial gain." So far, agents haven't found anything, he said.

As the FBI investigation continued, new details about the Walker family came to light from interviews with friends, family and acquaintances and from an examination of public records.

From these sources, an apparent contrast emerged in the life styles of the senior Walker -- known as Johnny -- and his former wife, Barbara Joy Crowley Walker, also 47.

While Walker was flying his single-engine airplane and otherwise enjoying an affluent life style as a private detective in Norfolk after retirement from the Navy in the mid-1970s, Barbara Walker was living in Skowhegan, Maine, working as "cementer" in a shoe factory and earning $2.65 to $8 an hour.

Warren Chapman, plant manager of the Dexter Shoe Co. in Skowhegan, said that Barbara Walker worked in the factory from Jan. 23, 1978, to July 16, 1984.

As a "cementer," Mrs. Walker would "cement edges of shoes together," Chapman said. Later, she worked in the "iron-on" section, molding the tops and bottoms of shoes together.

Mrs. Walker was paid the minimum wage of $2.65 an hour when she started in 1978 but was earning $7 to $8 an hour by the time she left, Chapman said.

He described Mrs. Walker as a "very dependable worker, very cooperative, always willing to work extra hours."

The two younger Walker children both attended high school in Skowhegan, school officials said. Cynthia was enrolled from September 1977 until June 1978, when she apparently graduated. Michael attended the Skowhegan school from September 1978 until June 1980.

At that point, he apparently moved back to Norfolk to live with his father and attend Ryan Upper High School. Michael graduated from Ryan in June 1982, according to Navy records.

When Mrs. Walker left Dexter Shoe Co., she left as a forwarding address a post office box in West Dennis, Mass., a small tourist community on Cape Cod.

She couldn't be reached for comment last night.

The Walkers were married June 4, 1957, in Durham, N.C., and divorced June 22, 1976, in Norfolk, according to papers on file in the circuit court in Norfolk.

They had four children: Margaret Anne, 27; Cynthia Marie, 26; Laura Mae, 25, and Michael Lance, 22.

In the divorce case, Walker agreed to pay $500 a month in child support. Mrs. Walker didn't receive any alimony, but the divorce decree contained a stipulation that she receive a $10,000 cash payment from Walker when the divorce became final.