FBI agents investigating an espionage ring allegedly headed by John Anthony Walker Jr. have focused their attention on female friends of Walker to see if they aided or protected him, according to sources close to the case.

One suspect, Laurie Robinson, has failed a polygraph test administered by the FBI, a knowledgeable source said. Robinson, a close friend and business partner of Walker, denies any knowledge of the alleged espionage ring and said yesterday that agents are "grasping at straws."

Robinson said she and members of her family have been questioned repeatedly by FBI agents and that she has been told she is a suspect. Despite her assertions that she was not involved, she said, "They seem to think I'm protecting him."

"As far as cooperation, they've had the utmost from me," Robinson said in an interview at a Virginia Beach restaurant.

"They just maintain I know more than I know," she said. "I don't know anything about the things they think I know."

A second woman, P.K. Carroll, has said through her attorney, Jim McKenry, that as a Norfolk police officer, she once identified the owner of a vehicle for Walker through a license check. McKenry said Carroll, who dated Walker for about three years and worked for his detective agency, was not involved in the alleged espionage operation.

McKenry said Carroll has not formally been advised that she is a suspect, "but she suspects so."

A third woman, a former secretary to Walker, has been been investigated but authorities have largely ruled her out as a suspect, a source said.

While the FBI has concentrated heavily on Robinson and Carroll and to a lesser extent on the former secretary, one government official familiar with the case said agents are investigating other individuals as well.

"The focus is not just on those three," he said, adding, "it may turn out that nobody else is involved."

Walker, of Norfolk, a retired chief Navy warrant officer, is accused of running one of the most damaging spy operations in 30 years with the help of his son Michael, his brother Arthur and a close friend, Jerry Whitworth. All four have been indicted on espionage charges.

Robinson and Carroll have been subpoenaed to testify Tuesday before a federal grand jury in San Francisco, according to McKenry, Carroll's attorney, and another individual knowledgeable about the case. The grand jury is believed to be investigating what happened to hundreds of thousands of dollars that the four accused spies allegedly received in return for Navy secrets.

Robinson, who owned a Virginia Beach detective agency with Walker, said she has told FBI agents repeatedly that she had "no prior knowledge" of Walker's alleged espionage activities but that she can't seem to persuade them.

She said agents have questioned her repeatedly about trips that she took with Walker, asking if she had noticed anything unusual. She said Walker tended to drive around in circles to make sure no one was following him, but that, she added, is standard practice for detectives.

"It's routine to always watch out for your 6 o'clock and your 12 o'clock -- in front and behind you," she said.

Robinson said Walker sometimes traveled out of the country, but she said she assumed the trips were for pleasure. Authorities have said Walker may have met Soviet contacts at various foreign locations.

She said that in light of Walker's arrest on espionage charges, some elements of his behavior "possibly seem suspicious now" but "they didn't seem suspicious then."

Robinson, a 30-year-old former model with a poised manner, described the continuing round of FBI interviews as "devastating."

"We're not talking to them anymore," she said of the FBI. "There is just nothing else to say."

Robinson has said she bought Walker's share of the detective agency, Confidential Reports Inc., after his arrest.

McKenry said Carroll, who broke off her relationship with Walker after his arrest May 20, is attempting to find a job doing security work. Carroll lost her job with the Norfolk Police Department last month, apparently after it was learned that she had run the license plate check for Walker, McKenry said.

Carroll has turned down requests for interviews.

Another friend of Walker, Roberta Puma, 35, had said earlier that she may have unwittingly aided Walker in delivering documents to his Soviet contact.

While an employe of Walker in 1977, Puma said, she dropped off a bag in the Rockville area that she believed contained trash. She said Walker instructed her to follow an elaborate route marked by soft drink cans to the drop site and to relay cryptic messages about her progress over a CB radio.

Puma said Walker paid her $1,500 for her assistance, but that she kept at most $500, returning the rest to Walker.

According a source, federal authorities gave Puma immunity in return for her testimony about the incident. A source said agents also offered immunity to Robinson, but that she turned the offer down, saying she had given them all the information she had.

In Baltimore, a federal judge yesterday denied Michael Lance Walker's request to be transferred from a correctional facility to a halfway house in Norfolk. Judge Alexander Harvey II said that at a halfway house, "no condition or combination of conditions exist that will reasonably assure" that Walker would appear at his trial.

Describing the espionage charges against Michael Walker as "very serious," Harvey said the weight of the evidence against the defendant and his lack of community ties made him a poor risk for a move to a less restrictive environment.

Walker's attorney, Ellen Hollander, argued that it would be appropriate to place Walker, 22, in a halfway house because he was not likely to leave Norfolk. "He is married, he has no prior criminal records and he has no history of drug or alcohol abuse," Hollander said. In addition, his in-laws were willing to pledge their property -- worth an estimated $100,000 -- as collateral.

But Assistant U.S. Attorney Michael Schatzow said any move to place Walker in a facility with little security was impractical -- particularly because the government believes Walker will be convicted and is likely to serve a long prison sentence.

"Where he is being held now is not the black hole of Calcutta, nor is it a country club," Schatzow said about the jail where Walker is being kept. Authorities have refused to identify the jail.

Although representatives of the halfway house have agreed to take Walker if requested, it does not have guards and could provide no assurance that Walker would appear for trial, Schatzow said. The offer by his in-laws, while generous, should not be viewed as a promise that Walker would appear, he said.

"Why would this defendant stay around for trial?" Schatzow said. "He has no children. He's been married a relatively short time . . . . (The property) is not his property. It's his in-laws' property . . . and it's no loss to him if his in-laws lose their property."

Rachel Walker, Michael's wife, sat quietly during the two-hour hearing, winking at her husband when he entered the courtroom and at times shaking her head during arguments presented by the prosecution. She would not comment on the judge's ruling but did say she was living in Norfolk and visiting her husband once a week in Maryland.