JUST when 10-to-14-year-olds most need guidance in making the critical transition from childhood to adulthood, they are often given too much autonomy and too little support from adults.
The result is that the nation's 19 million young adolescents, are ''the most neglected, least understood'' segment of American society, researchers say. Without more help from ''pivotal institutions'' - parents, schools, community and health-care groups, and the media - a significant portion of these youths risk becoming ''lifelong casualties'' of drug and alcohol abuse, pregnancy, AIDS, suicide, and violence.
These are some of the conclusions of a seminal study by the Carnegie Council on Adolescent Development released today.
A decade in the making, the report was compiled by a panel of 27 national leaders from diverse fields. It offers broad-based recommendations for change.
''This transition into adolescence is a much more serious, dangerous passage than most of us experienced when we became adolescents,'' says Ruby Takanishi, executive director of the council. ''We tend to forget that they're really still children and not yet adults. They're very vulnerable.''
That vulnerability, Dr. Takanishi says, has been heightened in recent years by dramatic changes in family structure and greater pressure to drink, smoke, use drugs, and have sex. Statistics tell part of the story:
* Two-thirds of eighth-graders say they have tried alcohol. One-fourth say they are current drinkers, and 28 percent say they have been drunk at least once.
* Marijuana use among eighth-graders more than doubled between 1991 and 1994, from 6.2 to 13 percent.
* Girls ages 15 and younger are experiencing the greatest rate of increased births, although the number of births is still not large.
* The suicide rate among young adolescents increased 120 percent from 1980 to 1992.
David Hamburg, president of the Carnegie Corporation in New York, blames some of the widespread neglect of young adolescents on two misconceptions.
First, he says, the growth spurts and mood shifts of puberty contribute to a stereotype that this age group is hard to deal with. Second, even professionals have mistakenly encouraged adults to ''get out of the way'' and let young people chart their own path to independence.
''That's sort of convenient to believe because it lets adults - teachers, parents, doctors - off the hook in terms of responsibility,'' Dr. Hamburg explains. The revised professional consensus, he says, calls for letting students gradually move toward greater autonomy over several years.
Young adolescents themselves confirm the need for that approach. ''In surveys they say they want more adult and parental and family attention than they're getting,'' says Takanishi, the mother of a 13-year-old.
Beyond family support, Carnegie researchers emphasize the importance of ongoing parental involvement at school. ''Parents who are heavily involved in elementary school tend to drop out later,'' Hamburg says. ''Evidence shows that's bad for their kids' academic achievement and social involvement.''
As one way of improving education for 10- to 14-year-olds, the council recommends that teachers receive specific training for middle school. It also suggests breaking schools into smaller units, such as academic houses or schools within schools.
''It's not difficult to do and it's not expensive,'' Hamburg says. ''The advantage is, it's much easier for each child to have more individual attention and more personal relationships.''
Students also need community support in using after-school hours constructively, the report states. Takanishi cites a Justice Department study showing an upsurge of juvenile crime from 3 p.m. to 6 p.m., when adolescents are typically unsupervised. Other new evidence, she adds, ''strongly documents a clear relationship between involvement in organized activities and reductions in school dropout, drug abuse, crime, and adolescent pregnancies.''
Hamburg also calls for more community-based parent-education and parent-support groups. Noting the popularity of these ''mutual aid societies'' among parents of infants and young children, he laments their scarcity for families with adolescents.
In the business world, the council urges employers to offer policies and practices that support family needs. A corporate refusal to spend advertising dollars on violent or sexual television programs, it adds, would encourage better entertainment for young viewers.
The council acknowledges that greater support for young adolescents will require new expenditures, both public and private. But it argues that wiser use of existing funds will offset some of the increase. Moreover, Hamburg says, ''Preventing the damage now occurring would have a powerful social and economic impact.''
Although early adolescence is more neglected than any other phase of life, he says, ''there's a huge opportunity. While kids are trying things out, we have a good opportunity to shape healthy lifestyles and help them get on a good longer-term course. They're very plastic at this time. They're open to constructive influences.''