''The kind of abuse that leads to multiple personality,'' said Dr. Braun, ''is frequent, unpredictable and interspersed with love. As children, the multiples have known both love and abuse, and they string together one personality that experiences the good part, another that embodies the bad. The parent will be very loving one moment, then the next switch into a monster. Many of the parents of multiple personalities themselves seem to suffer from the disorder, and a surprising amount of the abuse comes from mothers.''

On average there are from 8 to 13 personalities in a typical patient, although there can be more than 60, according to Richard Kluft, a psychiatrist at the University of Pennsylvania who has studied more than a hundred cases.

Writing in Psychiatric Annals, Dr. Kluft describes some of the most common types of personalities: a ''host'' personality, typically the one who comes into treatment; a fearful, childlike personality; a competent protector; an ''inner persecutor,'' usually modeled after the abusive person, who tries to harm the other personalities, and an ''anesthetic'' personality, impervious to pain, that apparently arose to endure abuse.

In general, the more severe and relentless the precipitating trauma, the more personalities there will be. Many of the personalities seem to function as cushions against the pain of physical abuse. ''There seems to be a limit to how much trauma a given personality can bear,'' Dr. Putnam said. ''It's as though each were a buffer that, when filled, means a new one must be created.''

Multiple personality ''may mimic the gamut of psychiatric syndromes,'' according to a report in The Journal of Clinical Psychiatry, and is therefore often misdiagnosed. Depending on the personality involved, the diagnoses can range from schizophrenia and depression to epilepsy. The report urges clinicians treating patients who have received a plethora of diagnoses over several years and who have failed to respond to standard treatments to consider the possibility of multiple personality.

Estimates of the prevalence of multiple personality vary widely. Investigations, a research bulletin of the Institute of Noetic Sciences, which has supported some of the research, estimates that there may be as many as 16,000 people with the disorder in the United States, only about 10 percent of whom have been diagnosed. Other estimates range from one in 200 people to one in 10,000. According to an estimate by Dr. Bliss in a recent issue of The American Journal of Pyschiatry, as many as 10 percent of psychiatric patients may have the disorder, though almost none of them are so diagnosed.

Some Experts Are Skeptical

Other experts, though, are skeptical of the estimates, and see the diagnosis as faddish. Dr. Orne, for example, observes, ''There have been more cases of the disorder reported in the last 10 years than in the history of the world before.'' Corbett Thigpen and Hervey Cleckley, the psychiatrists who wrote ''The Three Faces of Eve,'' probably the best known account of multiple personality, have reported that out of hundreds of cases referred to them as possible multiple personalities, only one other actually had the disorder. Like Dr. Orne, Dr. Thigpen and Dr. Cleckley believe the disorder exists, but feel that it is far rarer than some others think.