FREDERICK -- Whether biological-warfare researcher Frank R. Olson's death from a 13-story fall in New York City 40 years ago was suicide or murder is a tantalizing question that, some say, never has been satisfactorily answered.

But sons of the late Frederick biochemist, whose top-secret work involved both the U.S. Army, which was his employer, and the CIA, hope to put the issue to rest by having a team of forensic scientists examine their father's body.

As the first step, his remains were exhumed yesterday from a hillside grave in Linden Hills Cemetery overlooking Frederick.

"We're looking for any indication to tilt the story one way or another," said Eric Olson, a 49-year-old psychologist who lives in Frederick.

"Maybe we've been told the truth, but it's hard to know that."

Frank Olson, who was a civilian researcher at the Army's Fort Detrick, plunged to his death Nov. 28, 1953, during a government trip to New York City.

His death was initially listed as a suicide. A complete autopsy was never conducted, however.

Twenty-two years later, after seeing a passing reference in a post-Watergate report on the CIA's illegal activities domestically on behalf of President Richard M. Nixon, Mr. Olson's stunned family learned that he had been an unwitting participant in a CIA experiment involving LSD.

"It's hard to come to emotional terms with something you don't quite understand," Eric Olson said yesterday, sharing old photographs of his father, who at the time of his death was a lean, balding man.

"It was complicated. In some sense, it was a relief -- something had come to light. But there was a lot of anger" among family members.

The family later received $750,000 in a pension-settlement from the federal government and then-President Gerald R. Ford personally apologized for Frank Olson having been a victim of a government experiment.

Eric Olson said the government had initially promised $1.25 million, but the amount was reduced after a congressman objected to the settle ment's size.

Despite the years and the settlement, many questions have remained unanswered.

Eric Olson said he and his brother, Dr. Nils W. Olson, a Frederick dentist, decided to have their father's body analyzed at this time because they are in the process of having him reinterred at Mount Olivet Cemetery in Frederick, where their mother and other family members are buried.

Their mother, Alice Wicks Olson, died last year. She was a well-known mental health counselor in Frederick County who pursued the case of her husband's death for many years before settling with the government.

The other family members buried in the cemetery are the Olson brothers' sister, Lisa Hayward; her husband, Gregory, and their 2-year-old son, all of whom died in a plane crash in 1978.

"This is the right moment to do this," Eric Olson said, referring to yesterday's exhumation.

He also said he has been told that other documents concerning his father's death may exist, despite earlier CIA contentions that all documents had been released at the time of the settlement with the family. He has not yet pursued that possibility, he said.

James E. Starrs, a family friend who is a professor of law and forensic sciences at George Washington University's National Law Center, cites several reasons why he believes Mr. Olson's death was a homicide.

Mr. Starrs, who is leading the team of scientists, anthropologists and criminologists on the project, said Mr. Olson knew of sensitive warfare studies at Fort Detrick and of clandestine CIA activities and that his reaction to LSD made him a security risk.

"We know he was given LSD," Mr. Starrs said. "Was he given anything else? We don't know."

Three days after taking the drug, the 43-year-old Mr. Olson became withdrawn and said he was going to quit his job. Shortly thereafter, Mr. Olson was sent to New York for treatment of LSD-related behavioral aberrations. He was accompanied by a CIA staff member.

About 1:30 a.m. Nov. 28, he plunged through a window -- in which the shade was drawn -- and fell to his death.

Other factors include conflicting accounts from Dr. Robert Lashbrook, a CIA scientist who was sharing the hotel room with Mr. Olson. Initially, Dr. Lashbrook said he had seen Mr. Olson fling himself out the window.

Later, however, he said he had been awakened by the sound of a flapping window shade and had not seen Mr. Olson fall.

Eric Olson, who has given up his psychology practice to write a book about his father's case, as well as other works about psychology, said yesterday that it is unlikely that a man would jump out a small, closed window with the blinds still hanging down.

He also found Dr. Lashbrook's reaction surprising -- after Frank Olson's fall, Dr. Lashbrook was found sitting on a toilet in his underwear, his head in his hands.

"He never came down to see what happened," Mr. Olson said.

"It's a stretch to imagine someone reacting that way. It's odd. But I'm not saying it's not possible."

Dr. Lashbrook, who is now 75 and lives in Ojai, Calif., said yesterday that he firmly believes that Mr. Olson did, in fact, take his own life.

"There's no question about it," he said, reiterating that he didn't see Mr. Olson jump.

Dr. Nils W. Olson, a 45-year-old Frederick dentist and Eric Olson's brother, did not attend the exhumation yesterday -- a process that took about 30 minutes.

His brother, Eric Olson said, has been busy with his dental practice.

Several attempts to reach Dr. Olson by telephone yesterday were unsuccessful.

As Eric Olson explained his father's case to reporters, most of them unfamiliar with the family's story -- which had been well-publicized in the mid-1970s -- Frank Olson's casket was taken to the Hagerstown Police Department Crime Laboratory yesterday where the forensic team was to start analysis of its contents.

The forensic team will analyze the remains for evidence of drugs and of fractures and injury to the bones that cannot be attributed to the fall, Mr. Starrs said.

During the initial autopsy, no X-rays were taken and little internal examination was done, he said.

Dr. John S. Levisky, an anthropologist and chairman of the behavioral science department at York College, will examine the skeleton for evidence of trauma and fractures. Yale Caplan, a toxicologist, will analyze hair, brain matter, fingernails and other bodily substances.

A report of the team's findings will be released next month.

The Olson family first became alerted that there could have been mysterious circumstances surrounding Mr. Olson's death in a report in 1975 by the Rockefeller Commission, which President Ford appointed to examine the role of the CIA in accumulating domestic intelligence on behalf of President Nixon.

The post-Watergate investigation, which was headed by the then-vice president, Nelson A. Rockefeller, concluded that the CIA had given unsuspecting employees LSD and other similar drugs in experiments dating back into the 1950s.

At least one such experiment resulted in a suicide, the report said. The Olson family realized -- and then verified -- that the death had been that of Frank Olson.