When the space shuttle Challenger swooped down to a perfect landing in mid-October, it should have been a joyous occasion in Clear Lake City, Tex., home to the astronauts and the Johnson Space Center. Instead, the community of 37,000 was in shock-mourning the deaths of six teenagers in the city and neighboring areas who had committed suicide since early August. The chain of deaths began when Paul Kuns, 19, shot himself in the head in his car--the first of three friends, all high-school dropouts, to kill himself. Six weeks later, Sean Woods, 19, did the same thing in his pickup truck. On October 4, a third member of the group, Wesley Tiedt, 19, was found hanged from the top of a stairway at his home. List grows. The suicide chain then spread beyond this circle of friends. On October 6, Lisa Schatz, 15, short herself. Three days later, Gary Shivers, 16, was found hanged in his garage. And on October 11, Darren Thibodeaux, 14, sealed off the family garage with towels, turned on the motor of a car and asphyxiated himself. It's emotionally so draining, says the Rev. Buddy Miller, minister of Clear Lake United Methodist Church, who held funerals for three of the six. A preacher faces suicide more often than most people in the community, but I've never had anything like this. The directors of the funeral home cringed every time the phone rang. The series of deaths in the space community is the latest example of what public-health officials call clustering--the phenomenon of teenage suicides in which one person's suicide triggers another in the same locale. There is much debate among mental-health specialists over whether some of these deaths are part of a chain or are coincidental. In any case, the clustering phenomenon has occurred against a background of increasing teenage suicides. Since 1970, the suicide rate for youths age 15 to 19 has risen 44 percent, compared with a 2.6 percent increase for the nation as a whole. In that same period, suicide has gone from the fifth leading cause of death among people age 15 to 24 to second leading cause, accounting for approximately 5,000 deaths a year and trailing only automobile and other accidents. This is a national tragedy of enormous proportions, comments New York Lt. Gov. Alfred DelBello, chairman of the state's Council on Youth Suicide Prevention. In a recent television drama about suicide, Silence of the Heart, the parents of a boy who killed himself talk the victim's best friend out of jumping off a cliff. After the show, suicide hot lines in many cities were swamped with calls. My No.1 purpose, says the film's director, richaard Michaels, is to communicate to young people who are deeply depressed or feeling suicidal that there are people who really care, and places they can go for help. In recent years, a growing number of communities have been devastated by suicide clusters. Other outbreaks. New York's affluent Westchester, Rockland and Putnam counties north of New York City were shaken by a string of 12 deaths. Police authorities are puzzled by some of the cases. More than half of the deaths were by hanging. One victim had told friends that he identified with a male character in the movie An Officer and a Gentleman, which features a suicide by hanging. Last year, the town of North Salem was stunned when a 17-year-old boy hanged himself three weeks after his girlfriend hanged herself. They had quarreled at a drive-in. In one New York State hanging case, authorities suspect the victim died accidentally in sexual experimentation. Another major cluster occurred in sprawling Plano, Tex., which in 10 years has grown from a farming community of 30,000 to an upper-middle-class city of 100,000 the beneficiary of the ripple effects of Dallas's booming economy. Acres of new subdivisions sport homes in the $100,000 range, and on many the wood-shingle roofs are so new they have not gained the soft-gray patina that indicates a settling in. In 1983, a high-school student asphyxiated himself four days after his best friend had been killed during a drag race. Inside of a week, another boy was found dead, and within 15 months the city had a total of eight youth suicides. As cluster suicides gain public attention, mental-health specialists are looking for reasons why young people may be susceptible to copycat suicides. Community stress may play a role. Glenn Weimer, a family counselor in Plano, notes that the city has undergone such rapid growth that few people have had time to put down roots. It is a community with high levels of divorce, single parents, dual-career families and affluence. There is a fertile soil for this kind of event, he comments. In many ways, Plano represents the American Dream of growth and upward mobility. The thing that scares me is that there is the opportunity for this phenomenon to occur anywhere in the U.S. where there are some of these factors, says Carole Steele, executive director of the Plano Crisis Center. The phenomenon of clustering is not confined to urban areas. Two years ago in Cheyenne, Wyo., population 47,264, three teenagers committed suicide in the month of April. For the rest of the school year, mental-health officials dealt almost daily with youngsters attempting suicide or having suicidal thoughts. It just mushroomed, says Raymond Muhr, director of the Southeast Wyoming Mental Health Center. Corresponding traits. Although many suicides appear to take place without warning, mental-health experts point out that there are some common characteristics in people who may be vulnerable to suicide. Some 70 percent of all teen suicides had alcohol in their systems, and 50 percent had recently had a physical altercation, according to Diane Ryerson of the South Bergen, N.J., Mental Health Center. In addition, most suicides had shown some from of disruptive behavior beforehand, comments Dr. Kenneth Schonberg, director of the Division of Adolescent Medicine at the Montefiore Medical Center in New York. This can be truancy at school, promiscuity, severe outbursts of temper, physical illness, excessive substance abuse--any number of things. It's seldom subtle, he says. Shifts in habits. Other warning signs include depression, changes in eating or sleeping habits, the giving away of prized possessions, talking about suicide even jokingly, a withdrawal from usual activities and friendships, and reaction to the loss of a relative, friend or parent. These warning signs occur in both single and cluster suicides. As the suicide rate continues to climb, health officials are examining the factors that tend to accelerate the phenomenon of clustering. When one suicide occurs, it brings other kids who are vulnerable to the surface, says Thomas Barrett, a psychologist for the Cherry Creek School District near Denver. Public attention to a suicide in the community also may take away some of the taboo feeling that people have. It can instill within someone else the idea that it's O.K., in effect giving permission by the fact that someone else has done it, says Barry Lawson, assistant director of the Comitis Crisis Center in Aurora, Colo. Psychologists believe that many of the at-risk teens are subconsciously crying out for attention and may find suicide the ultimate revenge. Observes Julie Perlman of the American Association of Suicidology: A kid may say, 'Look, he did it, and look at all the attention it got. People really felt badly, so why don't I do it?' For many young people, suicide may not be real. Often, teenagers may not appreciate the finality of death, says Dr. Michael Gorman of the Centers for Disease Control in Atlanta. The recent clusters in Plano, Westchester County and elsewhere are stirring up prevention efforts across the country. California has begun a pilot program at the junior-high and high-school levels to inform students about depression, feelings of despair and the risk of suicide. Residents of Plano set up their crisis center with $150,000 in community denations to start a hot line for potential suicides. Local churches strengthened family activities, youth counseling and programs aimed at educating people about suicide. In Clear Lake