The symptoms of the disorder are particularly bizarre -- so much so that many who suffer from it believe they are unique and go to great lengths to hide it, sometimes for 30 years or more. They hide it so well that until recently even those who specialize in its treatment apparently had grossly underestimated its prevalence.

They call it an obsessive-compulsive disorder, and, says Dr. Thomas R. Insel, staff psychiatrist at the National Institute of Mental Health, "that does not mean what is commonly used in cocktail party language, which has to do with people who are rigid and unemotional, stubborn and usually male. The way you hear people complaining about their husbands . . .

"That," he emphasizes, "is not what we're talking about. This is something quite different. This is not a personality style or a character defect. This is an illness."

Here's an example, as described by a patient of Dr. Insel's:

"If I am preparing something to eat for myself, such as a sandwich, I have an awful time worrying about the cleanliness of the food. I worry and obsess about certain specks that I see on the food. I worry that a certain speck might harm me if I eat it . . . Also I worry about specks on forks and spoons and knives . . . Even during eating I worry much about dirt specks on the food. This makes me angry and is humiliating because when other people in the family are at the table during a meal, they often notice me staring strangely at the food, and also picking at the food to remove any specks, which usually are probably harmless anyway."

An abnormal preoccupation with cleanliness is often a hallmark of the disorder, in both children and adults. In some cases handwashing may occupy five or six hours a day. The patients may recognize that their behavior is aberrant but are unable to control their compulsion.

Howard Hughes, says Insel, was apparently a classic case, probably the worse for having received no therapy, and for surrounding himself with underlings who reinforced the compulsion by catering to it.

According to Insel and to Dr. Judith Rapoport, chief of the NIMH Child Psychiatry Branch, the compulsions may often involve complicated rituals, like counting the same things over and over in one's mind for hours at a time. Because these compulsions often involve fears of hurting someone, they typically may have a person wondering (for no reason) if he hit something with his car, and then returning again and again to the place he obsessively believes this has happened.

Obsessive compulsives are characteristically late for everything -- school, work, appointments -- because of such behavior. They fight often valiently and futilely against the compulsions and, says Rapoport, when they do come in for treatment they almost always say: "I thought I was the only one in the world with these crazy symptoms and I didn't want anybody to know about them."

Until recently, most psychiatrists believed that persons with obsessive-compulsive disorders accounted for only about 1 percent of the psychiatric patient population. However, the results of the Epidemiologic Catchment Area (ECA) Surveys released last year by the National Institute of Mental Health suggested a far greater population, perhaps as many as 2 million people in this country with the disorder. The survey of some 17,000 residents of Baltimore, New Haven, North Carolina, St. Louis and Los Angeles was the most complete catalogue in recent times of the prevalence of mental disorders in the American population.

However, because the survey results were somewhat preliminary, notes Rapoport, the totals may have included people with different disorders. So the actual number of obsessive compulsives is probably not that high, although still significantly higher than most of them would have guessed.

Rapoport has dealt principally with childhood obsessive compulsives, while Insel, in the NIMH Clinical Pharmacology Branch, sees mostly adult patients. Between them, they believe they have the world's largest sample of obsessive compulsives.

Rapoport will describe some of her findings on children with the problem tomorrow at one of a series of NIMH meetings designed to disseminate current research among other NIMH scientists.

Neither Rapoport nor Insel can state definitively what causes the problem, although Insel notes that over the years, "in every era, people have found an explanation that fits the era. So that during the Victorian period, there was a nice psycho-sexual explanation." They cited the case of a Victorian adolescent boy who could not sit on a chair if a woman had sat on it before.

Although some behavioral counseling has helped some compulsives, there really is no cure. Both researchers, however, have demonstrated some success in controlling the syndrome with a tricyclic anti-depressant -- chlorimipramine -- a drug that works on the brain's serotonin system.

The drug is not sold in the United States (but is available in Canada), and it is not a cure. In scientific studies of both adults and children, however, it did ease symptoms. It had side effects, some adverse in the younger group, but because the disorder is so resistant to treatment, the drug is regarded as potentially useful in a condition Rapoport calls "severe and malignant."

In earlier work, Rapoport has identified some brain abnormalities in the CAT scans, or brain X-rays, of obsessive-compulsive patients. Some patients also do poorly on tests of spatial relationships, but the severity of their symptoms does not seem to correlate with the severity of the abnormalities.

Rapoport usually sees children at about age 14 -- with boys reporting onset of symptoms around age 9 and girls at 11 or 12. Insel has seen some patients whose symptoms began at around 19 and others whose symptoms didn't start until their thirties or forties. In any case, he says, they come for help when they become too depressed about the problem and can no longer maintain both the compulsive rituals and a relatively normal life.

Behavioral therapy and, where they exist, trials with chlorimipramine, are almost all that can be offered to victims. Parents of patients are encouraged to communicate with each other because they can inadvertantly reinforce the bizarre behaviors. "I've seen parents," says Rapoport, "get very sucked into the rituals, not that they believe them, but because they get so upset at how upset the child is."

One parent, for example, would touch the wall 100 times because the child was having a temper tantrum, or appeared to be in terror. Insel described one parent who had driven 20 miles in the middle of the night to buy more of a particular brand of soap. Says Rapoport, "They do it out of good feelings of not wanting the child distressed, but then they can end up being like the coterie around Howard Hughes."

"It is," warns an adolescent patient in an NIMH follow-up questionnaire, "like a stray cat on your doorstep. You feed it and it comes back again. The problem feeds on itself -- when you carry out the rituals, it strengthens them."

Finally, this 15-year-old writes, "Advice for the Doctors: Do not treat the patient as a specimen. I have been frustrated in the past by domineering, naive doctors who did not feel the problem . . ."