When a gunman shot and killed the manager of Bish Thompson's Seafood Restaurant in the middle of Wisconsin Avenue in Bethesda last March, the three eyewitnesses to the incident could provide police with only vague descriptions of the assailant.

But Montgomery County police Lt. James Robey, using an old pocket watch and his deep, soothing baritone, placed all three witnesses in a hypnotic trance and got each one to give a more precise description of the gunman, down to his clothing and full beard. The descriptions led to the arrest and indictment of Jackie Lee Hughes, whose trial for murder began last week.

Once dismissed as the hocus-pocus of magicians, hypnotism is now regarded by Montgomery County officials as a valuable investigative tool. Largely because of Robey, who has hypnotized almost 500 people since 1978, the county has pioneered the use of the technique in the Washington area.

In doing so, however, county police have gone considerably farther than any of their colleagues in other jurisdictions in endorsing a procedure that is still largely an unknown quantity and the source of some thorny legal and scientific problems.

Police spokesmen in Prince George's County, Fairfax and Arlington, for example, all said their departments had used hypnosis only once or twice in the past several years. In the District of Columbia, hypnosis can by law be used only by a psychiatrist or medical doctor, according to Deputy Chief Alfonso D. Gibson, and has only been used twice, "only when every other investigative lead has panned out to nothing."

Three states, Arizona, Minnesota and California, have passed laws banning hypnotically induced testimony from criminal courtrooms. In addition, New Jersey, while not banning hypnosis entirely, has laid down some strict guidelines for its use. Some legal observers expect those guidelines to become the nationwide standard.

Federal courts still have not taken up the issue. And the Federal Bureau of Investigation has guidelines so strict that hypnosis is rarely used in federal investigations.

Supporters of investigatory hypnosis, and they are many, argue that recollections drawn from hypnosis can and should be used in court as long as the hypnotist used proper care in questioning, so as not to "lead" the subject into inventing stories.

Dr. Daniel Sterne, director of the Baltimore-based Investigative Hypnosis Institute and the primary teacher of police hypnotists on the East Coast, calls hypnosis "a great tool. It works. Sometimes it works miraculously."

Psychologists and hypnotism experts generally agree that hypnotism more often than not can aid police in tracking criminals by enhancing the memories of victims and witnesses. Small details -- a license plate number, the eye color of an assailant -- that are easily forgotten by the conscious memory are believed to be stored somewhere in the subconscious, retrievable once the person is in a totally relaxed state of mind.

The debate over hypnosis comes over whether those facts recalled through hypnosis should later be used as evidence in courtrooms. Many times, the "facts" are wrong.

"The police have found a new toy, and they're going around hypnotizing people right and left," said Victor Crawford, who is representing Hughes in his trial in Montgomery County Circuit Court. "All over the country, police officers have started to use this, and injustices have come to light."

"It was never intended to be used for how police are using it," Crawford added. "It is a trick, a sideshow for carnivals. It's very dangerous to take what somebody says under hypnosis as truth."

The Montgomery County Police Department's use of hypnosis is largely the result of Robey's personal interest in a subject that has fascinated him since childhood.

After attending a seminar on new techniques in police science, Robey persuaded the Montgomery County Police Department to allow him and a colleague to become trained in hypnosis. Robey attended courses in hypnosis across the country, and now works his magic for other police jurisdictions and in demonstration projections in classes.

Robey said that when he first hypnotizes his subjects, "The first thing I do is try to get them to relax." He said he uses an old pocket watch, rather than a spot on the wall, because a watch is common to most people and the sweep second hand can be entrancing.

Montgomery police have no set policy, he said, on when to use hypnosis in a criminal investigation. "I wouldn't call it routine," Robey said, adding that he alone usually makes the determination as to whether all other possible investigative techniques have been exhausted, and whether a particular witness might have something worth saying hidden in his subconscious.

Robey has decided to use it in a surprisingly large number of cases. Of the 500 people he has hypnotized since he first took the course in 1978, most of the subjects were crime victims and eyewitnesses, he said. He added that the hypnosis has been successful in leading to arrests and convictions in an overwhelming number of cases.

Once the information has been obtained, the state's attorney's office must decide what evidence to use in court. State's Attorney Andrew Sonner said that while he has some problems with hypnosis, it has been helpful in numerous prosecutions, such as the Calhoun case. However, he said he is somewhat more cautious now, after a decision last July by the Maryland Court of Special Appeals tossing out a conviction where hypnosis was used.

In that case, a victim of child molesting in St. Mary's county had been put under hypnosis to recall the events of the attack. But the appellate court essentially told the lower courts to decide the scientific accuracy of testimony drawn from hypnosis. The debate over that question is now being played out in courtrooms across the state.

Last week, Montgomery County Circuit Court Judge John McAuliffe ruled that two of the eyewitnesses in the Bish Thompson murder case could testify before a jury as to what they remembered about the murder after having their memories enhanced through hypnosis. Those eyewitnesses are considered pivotal for prosecutors to convict defendant Hughes of murder in the death of the restaurant manager, Robert G. Edwards, 32.

But at the same time, McAuliffe threw out one of those hypnotically induced descriptions, citing what he called "the dangerous potential for the use of hypnosis." For that witness, there was no written record of the police interview, and McAuliffe said he feared any witness under hypnosis could, with a little prompting, be easily led to describe things they never saw.

The reason is that hypnotism remains a largely mysterious phenomenon, even to those who practice it.

"A person can hallucinate, a person can lie," said Dr. Wladyslaw Michaluk, director of the Washington-based Institute of Applied Natural Science Hypnosis and Self-Hypnosis Training Center Inc. "A person can make up stories from comic books, or from newspapers."

"The testimony of hypnotized persons cannot be used and should not be used" in court, Michaluk said.

The American Psychiatric Association likewise has taken a generally dim view of hypnosis by police investigators. The association's policy, unchanged since the 1960s, is that hypnosis "be done only by a psychiatrist or psychologist," and then only for therapeutic reasons, said public information spokesman John Bonnage.

The American Bar Association has a committee now studying hypnosis to eventually form an official policy. The American Trial Lawyers Association has not yet taken a position.

Hypnotists point to a tendency of hypnotized persons to sometimes fabricate details, a phenomonon known as "confabulation." The word essentially describes a scenario in which a crime witness really did not see a specific detail at a crime scene, but the witness, under hypnosis, so wants to please his hypnotist -- the "master" -- that the witness will sometimes invent the details he does not know.

Scientists, lawyers and police journals all relate the same stories, one of a man under hypnosis who invented an elaborate tale about how Russian invaders had landed in the United States, and another about a woman who once told her hypnotist that she was living in Victorian England.

Sterne, head of the Investigative Hypnosis Institute and the hypnotist who trained Robey, has testified across the state in recent weeks, telling various county courts that properly trained police hypnotists usually elicit only factual information from their subjects. Sterne said he agrees with Judge McAuliffe, that hypnotically enhanced testimony should be allowed only when there is a written record of the hypnotism session, to make sure the questioner did not plant answers with his subject.