In a study at the University of Pennsylvania, college students who had attempted suicide were most often prompted by trouble at school, with their families, or in a dating relationship. For women the crisis was most often interpersonal, usually breaking up with a steady boyfriend; for men it was usually an academic setback.

''The teen-ager who attempts suicide is not always an obvious failure,'' said Aaron Beck, a psychiatrist at the University of Pennsylvania, who has done much research on depression and suicide. ''It is often a relative discrepancy between aspiration and performance - one 13-year-old, for example, tried suicide after he had been passed over as editor of the school paper.''

In the study of a cluster of teen-age suicides in Westchester County, Dr. Phillips found that those involved did not know each other directly, but all knew of each other. Hearing about another teen-ager's suicide can put a teen-ager at risk when several other psychological factors are at play, according to Dr. Shaffer. 'Impulsively Kill Themselves'

The teen-agers who kill themselves are not always depressed for long periods before, according to Dr. Shaffer.

''Some go through quick mood swings up and down - intense anger, fear, depression - which can be short,'' he said. ''But they can impulsively kill themselves in that brief period.''

The suicide attempt often comes as the teen-ager is anticipating a crisis, but before the true consequences are known, Dr. Shaffer said.

''Over half of teen suicides have had someone in their near family who attempted or committed suicide himself,'' said Dr. Phillips.