A Howard County police officer reached the scene of a crime recently only to discover that a red car he had passed on the way contained a possible suspect in the assault. Unfortunately, the officer could not remember the number of the car's license plate.

After a police department consulting psychologist placed the officer in a hypnotic state, the policeman was able to recall the license number exactly.

In Alexandria last year, a possible murder witness was hypnotized to refresh her memory. The precise details she described while under hypnosis helped police rule out a suspect in the case.

The use of hypnosis to aid police in criminal investigations is still relatively new, but increasingly, police departments in the metropolitan area are turning to hypnosis as an investigative tool to penetrate the subconscious memory bank of a victim or a witness for details to solve crimes.

"It's not hocus-pocus," said FBI behavioral science chief Larry Monroe. "A lot of the mysticism has been taken away from it and it is gaining a lot of respectability."

"The more sophisticated our knowledge of the brain, the more we know about information you can recall," said Sgt. Mark Paterni of the Howard County police investigative bureau. "We thought we would be remiss not to try out hypnosis."

Hypnosis, a technique sometimes used by psychologists to bring out a subject's subconscious memories, involves inducing a sleeplike state in which the subject is highly responsive to suggestions and commands of the hypnotizer.

While some objections to the technique have been raised -- largely by psychologists who disapprove of this particular use of hypnosis -- state and U.S. judges have been liberal in allowing information gained through hypnosis to be used as evidence.

More often, however, police find hypnosis valuable because the information it helps them obtain then leads them to other evidence.

The most celebrated instance of this came when police, investigating the Chowchilla, Calif., kidnapping of a busload of school children, hypnotized the schoolbus driver and thus discovered the complete license number of the suspects' car.

Locally, the use of this technique was highlighted when Assistant U.S. Attorney Barry Leibowitz, who was shot and wounded Dec. 20 as he was about to enter the federal courthouse here, was later hypnotized by investigators trying to get a more precise description of his assailant.

During a 3 1/2-hour hypnotic trance induced by a private specialist, he was able to remember that the gunman had a full beard. Leibowitz provided other details that enabled a police artist to put together a composite drawing that law enforcement sources said bears a striking resemblance to Robert Earl Lyons, the man charged with the shooting.

Police departments locally have used it to identify license tags and marks such as facial scars on crime suspects as well as to gain descriptions for composite drawings of suspects.

Most area jurisdictions, with the exception of Arlington and Fairfax City, the past two or three years after other investigative leads have been exhausted, according to local police investigators.

Montgomery County, however, has carried its use a step farther by becoming the first local jurisdiction to permit two officers to become trained and certified in "investigatory hypnosis."

Since November, Lt. James Robey and Cpl. Thomas Lechner have enduced hypnotic states in victims and witnesses in three rapes, three attempted rapes, one shooting and four robberies. In all but one instance, they obtained information that furthered their investigation.

"In one case," said Lechner, "we received very intricate details of the perpetrators of the rape and ther vehicle."

But he as well as the prosecutor in the Leibowitz case declined to provide further details of what they have learned through the use of hypnotism.

The Leibowitz shooting is the first time hypnotism has been introduced to buttress other evidence in a case in federal court here, and only in the past few years has the technique been used by local police departments.

"We're venturing on new ground," said a U.S. prosecutor in the Leibowitz case, "but we weighed matters and decided to go ahead." He said prosecutors expected a defense challenge to the admissibility of Leibowitz' statements under hypnosis and they taped the entire session "to protect ourselves."

In general, state and local courts around the nation have permitted descriptions made under hypnosis to be admissible in trials but have left it up to juries to decide how much weight to give to hypnotic-induced evidence.

Last October, in another California case, the U.S. Supreme Court let stand a first-degree murder conviction obtained with the aid of a prosecution witness whose memory was jogged by hypnosis.

Police investigators in the Washington area and the FBI say, however, that they always corroborate testimony under hypnosis with other evidence. They also only use it on victims and witnesses submitting to hypnosis voluntarily and never hypnotize suspects because of their Fifth Amendment right against self-incrimination.