Dr. Clark said that the pattern of manipulated cult conversions may not appear especially radical to outsiders, since no one is beaten or otherwise physically harmed. ''But hundreds of ex-cult members and their families have attested to the enticement practices of these groups,'' he said. ''Under the force of the conversion experience, people disappeared from their families and changed, sometimes after only a few days.''

Dr. Clark is one of the founders of the Boston Personal Development Institute, a nonprofit group that treats former cult members and advises their families. He and his associates there have treated former members of the Unification Church, the International Society for Krishna Consciousness, Scientology, the Way International, the Divine Light Mission, the Children of God, the Church of Bible Understanding and smaller, less-prominent groups. From the Middle Classes

The majority of those studied by Dr. Clark were from the middle and upper middle classes and ranged in age from 15 to 31. Most of those treated by Dr. Cath range in age from 13 to the mid-20's, but some are in their 50's and older. Their average age is 19 1/2. More are male than female.

Frequently they are intelligent youths from sheltered environments who have had contact with religion but rejected it, Dr. Cath says. He believes that many have a history of failing to achieve intimacy, of blaming others for their failures and of constantly striving for perfectionistic goals.

But Dr. Clark feels there is no standard profile of the ''destructive-cult victim.'' ''Orthodox psychiatric opinion has generally viewed conversion to deviant groups as a function of longstanding conflicts within individuals,'' he said. ''Our evidence strongly suggests that these individuals are succumbing to pressures within the cult milieu - pressures that can induce radical personality changes as easily in normally developing people as among disturbed ones.''

Dr. Singer said that the 700 cult members she had studied presented a wide range of personality types. ''You don't have to be a certain kind of person to succumb to the cults,'' she said.