Prince George's County State's Attorney Arthur A. Marshall Jr. has no current plans to subpoena before a county grand jury three people who police have said were with University of Maryland basketball star Len Bias when he collapsed after using cocaine, according to a source familiar with the investigation.

A crucial element in the case is what happened in Bias' room before he collapsed, and investigators believe the answers probably can be provided by those three men -- teammates Terry Long and David Gregg, who lived in the dormitory with Bias, and Brian Tribble, a friend of Bias.

Marshall has put off subpoenaing the three, however, because Maryland law automatically grants immunity from prosecution to those who testify before grand juries investigating drug crimes, the source said.

Marshall plans to begin issuing subpoenas for other witnesses July 7.

Last week, Marshall announced that he has discussed possible immunity with Alan Goldstein, the lawyer for both Long and Gregg.

Long, Gregg and Tribble have refused to discuss Bias' death with Prince George's detectives investigating the case, and the police cannot compel them to answer questions. Lawyers for all three have contacted Marshall, however.

Immunity is used by prosecutors as a tool to force reluctant witnesses to give incriminating evidence to a grand jury. Once granted immunity, witnesses can no longer invoke the constitutional right against self-incrimination and can be jailed for contempt of court if they then refuse to answer questions.

Prosecutors generally are selective about offering immunity, trying as much as possible to avoid granting it to those most responsible for a particular crime. Most often it is offered to witnesses believed to have crucial evidence that would incriminate the perceived targets of an investigation.

The situation is particularly complicated in Maryland because the state has more restrictive immunity provisions than the federal government.

Federal prosecutors have blanket authority to give immunity regardless of the offense. But Maryland law provides for immunity only for certain crimes, such as narcotics and gambling. For example, Maryland law does not provide for immunity to be given in manslaughter cases.

Marshall has said that while the focus of the Bias investigation is on drugs, the grand jury may turn up evidence that could lead to manslaughter charges being filed against the person who supplied Bias with the cocaine.

Lawyers interviewed yesterday said it is unclear whether immunity can be granted in the Bias investigation because of the possibility of manslaughter charges.

The experts said that Maryland law is not clear on whether immunity granted for gambling or narcotics offenses could be extended to other crimes, such as manslaughter, for which there normally is no immunity.

Legal observers said Marshall can be expected to argue that if he grants immunity under the drug statute, then a witness could not be prosecuted for any other crimes.

The Maryland Court of Special Appeals, the state's second highest court, has made one ruling that might be applicable. Acting in a case involving a grand jury investigation of gambling, it sided with defense attorneys who argued that their clients could not be forced to testify because evidence developed in the case could result in them being charged with income tax evasion. Tax offenses, like manslaughter, do not have immunity provisions.

The case is now on appeal to the Maryland Court of Appeals, the state's highest court.

If defense attorneys in the Bias case successfully argue that any immunity offered by Marshall would not apply to possible manslaughter charges, experts said, then Marshall may not be able to force potential witnesses such as Long and Gregg to testify before the grand jury.

Gregg, Long and Tribble came together with Bias in the early hours of June 19 to celebrate Bias' selection by the Boston Celtics in the National Basketball Association's annual player draft.

Police are known to be looking into the activities and background of Tribble, a one-time Maryland junior varsity player who lived in an apartment near the campus.

Sources have said that Bias visited Tribble's apartment about 12:45 a.m. the day he died and that Tribble went with Bias back to his dorm suite, where they were joined by Gregg, a 19-year-old freshman, and Long, a junior.

In another development, law enforcement sources said yesterday that Prince George's police want to talk further with D.C. police officer John Walker, a Bias relative who retrieved the athlete's personal effects from his dormitory room and sports car.

A D.C. police official said county investigators consider Walker a close friend of Bias who may have gone to Leland Memorial Hospital in Riverdale, where Bias was pronounced dead at 8:54 a.m. on June 19, about 2 1/2 hours after he collapsed in the dormitory room. The chief state medical examiner determined that Bias died of "cocaine intoxication" minutes after ingesting an unusually strong dose of the drug.

County police are attempting to find out what Walker may know about Tribble and other Bias acquaintances and what information he has about the use of Bias' Nissan 300ZX sports car, according to the D.C. police official.

Walker, who is assigned to the 1st District in Southwest Washington, has talked to county police once, a county police source said. Walker could not be reached for comment yesterday.

Prince George's police are looking into who drove Bias' car to the hospital in Riverdale and back to the Maryland campus in College Park. University police impounded the auto the day after Bias' death and found cocaine inside the car, county police said.