The FBI arrested a fourth Navy man today on a charge of espionage, expanding the known scope of an alleged Soviet spy ring outside the Norfolk family of retired Navy communications specialist John Anthony Walker Jr. and to the West Coast.

Jerry Alfred Whitworth, 45, a retired senior chief radioman who had access to "extremely sensitive" information about secret codes, according to an FBI affidavit, surrendered to FBI agents at the bureau's San Francisco office about 3 p.m. Pacific Daylight Time, FBI Director William H. Webster announced in Washington.

Whitworth was charged with conspiring with Walker and others, beginning in 1965, to pass secret information to the Soviets in return for money. The FBI said a search of Whitworth's home revealed a number of classified Navy documents dated 1975 to 1982, including many from the Naval Air Station in Alameda, Calif., one of his recent assignments.

The affidavit, filed in federal court here, revealed that a fifth person, "F," may be implicated in funneling defense secrets to Walker, and that Walker allegedly attempted to recruit his daughter, Laura Walker Snyder, into the espionage ring when she was an Army communications specialist.

The FBI believes Whitworth was an anonymous informant who first wrote to them last May offering to expose a major spy ring in exchange for immunity, the affidavit states.

Whitworth, currently unemployed and living with his wife Brenda in a trailer park in Davis, Calif., left the Navy in October 1983 after a 23-year career, according to the FBI.

Three other former and current Navy personnel have been charged with espionage: retired chief warrant officer John Walker, 47; his son, Navy seaman Michael Lance Walker, 22; and John Walker's older brother, retired Navy lieutenant commander Arthur James Walker, 50.

A federal magistrate in Norfolk today ordered Arthur Walker held without bail pending a preliminary hearing June 12 and appointed two attorneys to represent him.

FBI officials said today that agents are continuing to investigate whether other individuals are involved in what officials are terming the most serious espionage case in the past decade.

Whitworth, a tall and bearded man wearing a brown suede jacket, was ordered held without bail today by federal Magistrate Fredrick J. Woelflen. A detention hearing is scheduled for Friday.

"Mr. Whitworth, by virtue of his radio communications position, had access to some of the most classified communications data that we had," U.S. Attorney Joe Russoniello said after the hearing. "You would have to consider him a very critical player."

In the FBI affidavit, Whitworth is alleged to have fed John Walker information about classified naval maneuvers and other sensitive information from the early 1970s or before until his retirement and possibly beyond.

In addition to code information, Whitworth was trained in "sensitive satellite communications operations," according to the affidavit by FBI agent John H. Peterson.

The affidavit states that agents believe that Whitworth is the "D" mentioned in letters John Walker allegedly dropped for a Soviet agent at a rural site in Montgomery County the day before his arrest last month. Michael Walker is believed to be the "S" mentioned in papers seized from John Walker, and Arthur Walker is believed to be "K," according to previous affidavits.

The affidavit filed today states that another person, "F," had been identified by first name in papers found in John Walker's Norfolk house.

Whitworth served as a communications instructor at the Service School Command in San Diego from October 1970 through January 1973, overlapping duty there with John Walker, who was assistant director of the Radioman "A" School there from September 1969 through December 1971, according to official Navy biographies.

During the 10 years before his retirement, Whitworth held various positions, most involving security clearances and code communications, the FBI said.

The affidavit states that investigators have traced Whitworth's movements over several years on at least two Navy vessels and found that he was in Hong Kong and in the Philippines at the same time that Walker made trips there.

On both occasions, Walker is said to have "rendezvoused with his Soviet contact" after meeting with Whitworth. Whitworth's fingerprints were found on handwritten notes confiscated from Walker's house that appear to contain sensitive information, according to the affidavit.

The affidavit states that a person identifying himself as "RUS" wrote three letters, one of them postmarked Sacramento, to the FBI's San Francisco office last summer, offering to break up a "significant espionage system" in return for "complete immunity." RUS said the espionage ring included himself, a principal contact and at least three other members.

The last letter, however, said the writer had abandoned the idea of exposing the purported spy ring.

Agents believe that the person using the name "RUS" is the same person identified as "D" in the letters allegedly dropped by John Walker, the affidavit states. "It is further my opinion and belief that Jerry Alfred Whitworth is the person known as 'RUS' and 'D,' " the affidavit states.

According to the affidavit, agents linked Whitworth to "D" through the letters allegedly dropped by John Walker and through two confidential informants who told the FBI about a man named "Jerry Wentworth."

Among the items seized from Whitworth's residence were computer discs found to contain the "Dear Johnnie" letters left at the alleged "drop site," the affidavit states.

The affidavit also states that Arthur Walker told agents that John Walker had encouraged him to "operate like Jerry who was making big bucks by photographing classified documents."

Whitworth's lawyer, Louis Hiken, said at a news conference in San Francisco after the arrest today that he believed that agents illegally searched Whitworth's house on May 20, more than a week before they searched it again after having obtained a warrant.

Asked how the agents obtained entrance to Whitworth's house the first time, Hiken said, "They knocked on the door." He insisted that his client did not cooperate in the search, but he refused to comment further other than to say that Whitworth was innocent and had known John Walker for years only as a friend.

Walker's girlfriend at the time of his arrest, Norfolk police officer Pamela K. Carroll, said Walker had a business partner named "Jerry" who lived in the San Francisco area, her lawyer, James McKenry, said today.

"She knew he was a friend of Walker's, and Walker would go out several times a year and they had some business together," McKenry said. Walker told Carroll he had served in the Navy with "Jerry," but Carroll never met him during her three-year relationship with Walker, McKenry said.

He said he believed that Walker's most recent trip to San Francisco was six months ago.

Ted Ulrich, who worked with Walker at Wackenhut Corp., an international security firm, and in Walker's Virginia Beach private detective firm, Confidential Reports Inc., said last week that Walker had told him he had a business partner in San Francisco whom he visited a few times each year to collect profits.

Ulrich said Walker described the business as "some sort of amusement arcade."

Lavonna Peach, who manages the Rancho Yolo mobile home park in Davis, where Whitworth and his wife have lived for the last two years, said that about 10 people had been watching Whitworth's home for at least a week.

Harold Hatch, a neighbor, said he saw seven cars parked there today and a group of people who "went into the Whitworth home . . . and came out with briefcases and reading matter . . . . When they left, they left like a caravan. The whole seven went out, bingo, single file."

"I'm kind of stunned . . . to think of it happening in our park," Peach said.

In Norfolk this morning, U.S. Magistrate Gilbert R. Swink appointed two lawyers, including a former federal prosecutor, to represent Arthur Walker, who is accused of providing his brother with confidential documents from the Chesapeake, Va., defense contracting firm at which he worked.

Assistant U.S. Attorney Tommy E. Miller said Swink decided that while Arthur Walker was not without financial assets, the unusual circumstances of the case warranted two court-appointed attorneys. Miller said Swink ordered Arthur Walker to pay the court $200 a month to cover part of the defense costs.

Besides his military pension, Arthur Walker listed a $90,000 home in Virginia Beach and two Chevrolet automobiles among his assets in a hastily called hearing this morning, Miller said. Arthur Walker has been placed on leave without pay from his engineering job at VSE Corp., a defense contractor.

According to Miller, Arthur Walker told the judge he owed $20,000 on a first mortgage on his home and $7,000 on a second mortgage. Walker estimated the worth of the 1977 and 1962 vehicles at $2,200, Miller said.

J. Brian Donnelly, a former federal prosecutor who will represent Arthur Walker along with Samuel Meekins, said Swink may have appointed them to avoid the possibility of any later claim that Arthur Walker was denied his constitutional right to counsel because he did not have enough money to hire an adequate defense team.

Swink said during today's hearing that he expected that Arthur Walker's legal fees will amount to a substantial sum and that he was entitled to two attorneys because of the seriousness of the charges.

Meekins said that during an hour-long talk this morning with his new client, Arthur Walker mainly expressed concern for the financial welfare of his family. Arthur Walker is married and has three children.

Arthur Walker, a short, brown-haired man, appeared in court wearing gray pants, a beige shirt and brown shoes. He sat silently beside his attorneys during the afternoon hearing.

Meanwhile today, the Navy appeared to back away from its plan to consider whether to have John and Arthur Walker recalled to active duty so that they could be court-martialed.

"The Navy is not in any contest with the Justice Department," said Capt. J.B. Finkelstein. "It's simply that the secretary is looking at his options." He said a report is to be made Tuesday to Navy Secretary John F. Lehman.

Finkelstein's remarks came a day after Stephen S. Trott, head of the criminal division of the Justice Department, said the cases would be tried in federal rather than military court and that plea bargaining would not be allowed.

"It was never a plan to call them back," Finkelstein said. "It was simply a plan to to find out what our options are."