City dwellers across the country have reacted with outrage to last month's brutal rape and beating of a 28-year-old jogger in New York's Central Park. She was the last victim of an apparent rampage in which as many as 30 youths marauded through the park on a Wednesday evening and attacked nine people at random. The jogger, who is still in a coma two weeks after the attack, suffered the worst violence. She was raped repeatedly, beaten with a lead pipe, a brick and stones, and left bound and gagged in a pool of blood until she was discovered by passersby more than three hours later. Her brutalization was part of what the boys charged with the crime called a "wilding" -- or, as it's pronounced on the streets, "wil'ing." Eight youths, all from the Harlem neighborhood adjacent to the park and ranging in age from 14 to 17, were arrested the day after the assault. One of them, 15-year-old Yusef Salaam, is reported to have said in a written confession, "It was something to do. It was fun." Wreaking havoc for "fun" is nothing new. Twenty-five years ago, the British youths in Anthony Burgess's novel "A Clockwork Orange" talked about "doing the ultra-violence" -- going out and making mayhem just for the sport of it. "We can't do more than speculate about what made these kids do what they did," said Stanley Greenspan, a Bethesda psychiatrist and author of "The Essential Partnership." "But we can say what prevents the vast majority of kids from engaging in this kind of brutality. It's the traits they develop early in life: empathy and respect and concern for their fellow human beings." Greenspan said youngsters and adults who lack the internal means of controlling their aggressive impulses are vulnerable to being "swept away by the group process," as the youths in New York might have been. The psychology of adolescence may make teen-agers especially vulnerable to herd aggression. During these years, as psychologist Erik Erikson has described, the primary challenge is to reach a compromise between "identity cohesion" and "role confusion," leading to the "identity crisis." The importance of peer pressure is at a lifetime high. Because of this, juvenile delinquency is almost always a group affair. "Multiple kids are typically involved in most delinquent behavior," said James Breiling, a psychologist in the Anti-Social and Violent Behavior branch of the National Institute of Mental Health. "Peer influence has a decisive influence on what these children do." Breiling said research from the University of Colorado shows that if two children are equally alienated -- feeling adrift at school, having trouble relating to their parents -- and one takes up with a delinquent peer group while the other does not, the child who falls in with the wrong kids runs a 40-times higher risk of getting into trouble with the law. "In high-risk neighborhoods, kids are better off being socially isolated than having peers who encourage this sort of behavior," Breiling said.Greenspan, though, thinks adolescence has no special claim on herd aggression. Similar tendencies explain bizarre behavior at all age levels, he says, from fights at the local school playground to riots on the soccer fields of England. But the extreme brutality of the "wilding" that took place in Central Park resists easy explanation. How could these youngsters treat another human being as though she didn't exist? Maybe the answer lies in the psychology of the group. "What happens when you get into a group is that the arousal level gets heightened," said Suzanne Stutman, a clinical social worker and director of the Institute for Mental Health Initiatives in Washington. "Kids in groups don't have the same type of reality testing as kids alone," said Stutman. "They do crazy things a person wouldn't do if he was all by himself." News reports have emphasized that of the eight boys charged in the attack, only one had a prior arrest. Raymond Santana, 14, who was called the ringleader in the Central Park assault, was described by his junior high schoolteacher as "goofy, silly, the class clown . . . one of our nicest kids." He was being raised by his father and by a grandmother summoned from Puerto Rico a few years ago when the boy's mother walked out. A few of the others reportedly came from homes with one parent or both parents missing. But several were from intact or at least involved families. The father of Antron McCray, 15, was a Little League coach and neighborhood male role model and disciplinarian. Yusef Salaam's mother, concerned about a lack of a male influence in his life, enrolled him in a "Big Brother" program, and sent him to parochial school to get him away from the neighborhood kids. Michael Briscoe, 17, lived with his grandmother and went with her to church every Sunday, where he played drums with the choir. Some social commentators say the incident is an outgrowth of the boredom and frustration of ghetto life. "These are kids with nothing to do, with lots of idle time on their hands, because of cutbacks from conservative administrations in programs and recreational facilities," said Richard Majors, a psychologist at the University of Kansas who next month begins teaching at Harvard Medical School. "They have a lot of displaced anger," said Majors, "and they're taking it out on whatever is available." Majors sees these youngsters as victims of poverty in a conservative age. "Psychologists call it reaction formation -- a sense of displaced anger," he said. "These children are bored, looking for stimulation, entertainment." Does that mean any teen-ager, if he becomes bored enough and falls in with kids who are bad enough, can go on a rampage of brutality comparable to the one in New York? No, say psychologists. "You don't get good kids, decent kids, responsible kids suddenly attacking someone with this much viciousness," said Stanton Samenow, an Alexandria psychologist who specializes in delinquent behavior. "I'm willing to make a bet that if you looked at a videotape of the lives of each of these kids, this wouldn't be the first time they had done something like this." Susan Blumenthal, a psychiatrist and chief of NIMH's behavioral medicine branch, agreed that "these are probably not normal kids walking around. They have to have an underlying predisposition that makes them vulnerable to this kind of contagion." And in mob violence, the attackers tend to dehumanize their target. Samenow, author of "Before It's Too Late: Why Some Kids Get Into Trouble," said the youths he has treated who have committed comparable crimes "have the capacity to shut off their conscience. "They don't even see their victim as a victim."