Risky behavior that already has exposed 1 million to 2 million young Americans to acquired immune deficiency syndrome will become the habits of even younger Americans unless they are taught how to be careful. Age is not a barrier to infection. Adolescents are as susceptible to AIDS as adults are.

As of April 7, 15 American youngsters between the ages of 14 and 16 had developed AIDS. Ten of them are dead. Eleven of the 15 were hemophiliacs who had become became infected through their treatment with blood products.

The picture was different for Americans of college age. Among 17- to 21-year-olds, 200 had developed AIDS, of whom 108 are dead. Of the 200 cases, 125 were in gay or bisexual young men, and 16 were intravenous drug abusers.

In the 22- to 30-year-old group, there have been 4,800 people with AIDS, of which 2,440 are dead. In this group, 3,377 cases were in gay or bisexual and 884 in intravenous drug abusers.

The data show that infection is occurring in the mid- to late teens as individuals become sexually active and begin to use intravenous drugs.

Infection with the virus may not result in AIDS. In some persons, the virus remains dormant for years, perhaps forever. In others, it causes a spectrum of immune deficiencies and physical disability that does not meet the diagnostic criteria for AIDS. No one knows for sure how many people fall into these categories, although their numbers can be estimated from epidemiologic studies already done.

Almost 20,000 Americans have met the diagnostic criteria for AIDS, meaning they have developed the full-blown disease, and half have already reached the end of their lives. AIDS is a uniformly fatal disease within five years of diagnosis.

Most Americans with AIDS are in their twenties, thirties or forties, but they may have acquired their infection years earlier. The AIDS virus usually incubates four to five years from the time it enters the body until it causes the complicated set of signs, symptoms and illnesses called AIDS. That incubation period may be as short as several months, or perhaps as long as 10 to 14 years.

The two largest risk groups are homosexual and bisexual men, and intravenous drug users of either sex. Female sexual partners of men who are bisexual or use drugs intravenously also are at risk. For many of its victims, the publicity about AIDS came too late. They were already infected by the time the disease and its modes of transmission became well known. They acquired the infection because they followed behavioral patterns that were, for them, well-established.

Young adolescents may follow the same path, with the same disasterous consequences, unless parents either recognize their responsibilities to talk with their sons and daughters about this disease and its prevention, or, at least, let the schools do so.

Those talks need to begin early. Most children reach puberty by 13. Some are sexually active at 14. Inner-city mothers age 15 or 16 are not uncommon, especially in Baltimore and Washington. Gay sex, too, often gets under way by 16 or 17.

It may take only one bad contact to become infected. That contact may occur when the youngster is just beginning to explore his or her own sexuality, and is naive and vulnerable.

AIDS cannot alter sexual orientation. Parents who try to manipulate their gay son's fear of the disease into shame or fear about his sexual preference will more likely create a neurotic young man who will search for sex off the beaten path rather than seek a same-sex partner in whom he can invest emotional as well as sexual energy.

The boy who has no one with whom he can talk about his emerging homosexual feelings is unlikely to receive information in safe-sex practices that may keep him healthy. A hope is that both heterosexual and homosexual youngsters just becoming sexually active may learn safe-sex techniques and practice them as naturally as youngsters learning to drive automatically put on their seat belts.

Safe sex is not only for gay youths. The ninth-grade girl with a boyfriend who takes drugs by needle needs to learn the same principles.

Illicit drug use, unlike sex, is not a natural behavior. Keeping kids from shooting up is an even more important goal for parents, educators and counselors now than it was before AIDS appeared. But while focusing on that goal, they must also emphasize the need for youthful intravenous drug users to avoid sharing needles. Doing that is not sending a double message; it is just widening the margin of safety if programs to get kids to stop using drugs fail.

It is difficult to talk about these subjects to teen-agers, and parents may find it too uncomfortable to do so. They might then allow the schools to take over. Many school districts are now preparing for that task, with guest speakers, expanded sex and human biology courses, and educational films.

But if parents shut their eyes to the ways their children are sexually maturing, and if they do not support their local schools in providing realistic, practical education about AIDS, they are failing one of their primary obligations -- to protect their children.

Infection with the AIDS virus has far different consequences than a case of gonorrhea or an unwanted pregnancy.