It is at once a hall of science and a chamber of horrors. It is devoted to the study of violent death. Never mind that it is perhaps the foremost forensic museum in the world, it is an astounding place for the uninitiated.

The Museum of the New York City Medical Examiner, five floors above the city's morgue, offers testaments to the bizarre in the life of this city over the past 61 years. Crammed into one large room are glimpses into the lurid world that Weegee, the famous New York photographer, chronicled so well.

Each item, encased in formaldehyde or a glass vial, or locked in the still-life of a grotesque photograph, assaults sensibilities and at the same time pricks interest into the story behind it.

The man with the answers is Jean-Pierre Lahary, chief forensic technologist at the Medical Examiner's office, de facto curator of the museum and one of the world's experts in the reconstruction of mutilated bodies. Lahary was part of a team that identified 337 of the 346 victims of the Turkish airlines crash near Paris in 1974 from 18,000 separate body parts.

"Old Jean-Pierre is one very, very fine morgue man," said Dr. William Kirkham of the Civil Aeromedical Institute in Oklahoma City, Okla. Kirkham uses Lahary on an ad hoc basis to work on airplane disasters for the Federal Aviation Administration.

Lahary no longer notices the decapitated head that has rested in a jar of formaldehyde in the museum since 1925. "We still don't know who he is," he concedes.

He knows that jumping is the most common form of suicide, that women often apply makeup before taking overdoses of barbiturates, that men faint more than women do when confronted with gory sights and smells.

He knows toot hat purple skin color follows electrocution, that the right ear is better than the left one for identification, that the hole in a skull from a point blank pistol shot is star-shaped.

At 46, Lahary has seen it all. "People ask me what is the most unbeliveable thing I have ever seen. I tell them that the sensational doesn't exist here," he explains. "I have seen that everything is possible. Everything."

Lahary's reputation is particularly interesting since he has had no formal medical training. "I always have been interested in anatomy," he explains. "When I got out of college in Paris, my uncle, who was a judge, suggested that I try morgue work. So I did."

Lahary worked in the morgue in his naive Paris before moving to the United States 10 years ago. He finds that the Paris facility, compared to his current working address, is "like a neighborhood grocery store versus Macy's."

Lahary revels in the trade he has practiced for 17 years. Give him the most minimal remains of a human body, and he will identify it. Take the torso case last year.

An unidentified, mutilated one-armed torso arrived at the morgue. Within a couple of hours, Lahary determined that the man it once had been was 60 years old, 170 pounds, 5 feet 10 inches tall, with a 40-inch chest. The information was then disseminated to the New York police, who found that a man fitting that description had recently been placed on the missing persons list. An x-ray of the chest of the torso matched perfectly an earlier one of a 63-year-old man from the Bronx, and positive identification was made.

Lahary's skills have made him something of a celebrity.

A German television crew was in New York recently to interview him.

Lahary works as comfortably with INTERPOL, the sophisticated international police organization, as he does with New York City's finest. He hosts doctors and law enforcement officials from all over the world, who make a point of visiting the museum when they are in New York. He even shepherds groups of murder mystery buffs from Manhattan's Murde Ink, the well-known book store devoted solely to that genre of writing, who visit his museum a few times a year.

There are good reasons why the museum is in such demand. One is that the sheer number of homicides in New York City during the course of a year provides city medical examiner Dr. Michael Baden with ample material from which to select striking exhibits.

"This is the most important forensic museum in the world,' Lahary said proudly. "There are some 1,800 homicides a year in New York City. A city like Tokyo may have 100. Nowhere else comes close."

The museum was established along with the office of the city medical examiner in 1918. It was in Bellevue Hospital in those days, as was the morgue. Even Lahary shudders at the specter of morgue work in the days before refrigeration.

Since then, it has swelled with the memorabilia from untold numbers of murders, suicides and accidents. It was due largely to the 19-year tenure of Dr. Milton Helpern as city medical examiner from 1954 to 1973 that the field of forensic pathology has grown tremendously in importance to police work. Helpern was known throughout the world for his innovative detective techniques, and he made his office and the museum a Mecca of sorts for police and medical officials.

"Everything here is for legal or scientific purposes," Lahary explains. "If it is really weird, it can be used for didactive purposes."

It was something of a revelation, for example, to learn the causes of death among a number of women who worked in watch factories during World War II. Only after extensive autopsy work was it determined that they died of radium poisoning.

"They were painting the radium on thewatches so that they would be readable at night," Lahary said, pointing to a vial of radium in a display case. "The women would lick the radium on the ends of their paint brushes to make the points finer. No one knew how deadly it was."

Then, there is the strange case of the blue man. Using a large kitchen knife wrapped in plastic as a makeshift pointer Lahary targeted a small vial on one wall and began his tale. "The knife, it turned out, is the suspected murder weapon in a recent homicide and will be analyzed shortly for blood stains.)

"This man's skin was completely blue. That's why he was in the Barnum and Bailey Circus for 30 years. No one ever knew why his skin was blue. When he died, they performed an autopsy on him here. They found 103 grams of silver inside him," he said, again pointing to the vial full of silver. "He had worked in a silver mine when he was young, and the silver salts had affected his skin pigmentation."

Lahary interrupted his tour to talk to an attendant, who also had a story to tell.

"That's nothing, they brought a guy in here last week from Queens who had $55 in change in his stomach," he said, shaking his head, " $55."

A tour of the museum would not be complete without perusing the exhibits that go by the charming appellation of "therapeutical misadventures." One such incident involved the discovery during autopsy of two huge surgical clamps which had been left in a man's insides by accident during surgery 10 years before his death. As Lahary points out, the term "misadventure" is from a patient's point of view.

In what may be viewed as act of humanity, the museum is closed to the public. Not that most people would try to squeeze in a quick tour between the Guggenheim and the King Tut exhibit.

And that is as it should be. The museum is, after all, a forum for forensic pathology. Its danger is its side-show attraction. In their heyday, Barnum and Bailey would have loved to have acquired its contents to augment their collection of human freaks such as the blue man. Science, it seems, still offers the best - or at any rate the most peculiar - show in town. CAPTION: Picture, Jean-Pierre Lahary in the forensic museum; by Donal F. Holway for The Washington Post