DETROIT — At age 12, Ellen drew jealous stares from her friends when she walked down the street on the arm of her man. He was 16, lean and the hottest break dancer in the neighborhood. She was his girl.

But the honor came with a demand — he wanted sex. Ellen didn’t want to lose him and figured he wasn’t asking so much.

When Ellen was 15 and a sophomore at Martin Luther King High School in Detroit, she tested positive for the AIDS virus. She’s certain she got it from her break dancer, whom she hadn’t seen in a long while.

Matthew, who lives in the Detroit suburbs, believes he got infected at age 15.

Fortified one night by swigs of Jack Daniels from his mom’s liquor cabinet, he walked to a bar where he knew gay men cruised the parking lot.

As Matthew hoped, one asked him home.

“I never thought about any danger,” he said. “I just did it. There was something going on inside me — I wanted to be touched. I was like a ball of fire.”

Two years later, Matthew saw a doctor about a persistent fever and cough and found out he had the AIDS virus.

Brian doesn’t know when he got it. He says it could have been any time between ages 15 and 18, from any of dozens of girls. At the time, the dashing Detroit youth fancied himself a ladies’ man, and sex sure felt good.

Just a month out of high school, Brian was taking a physical to get into the Army when he came up positive.

Three young people given to the sexual adventuring so common among teen-Agers; three young lives among a growing number now beset with the deadly reality of AIDS.

Three more reasons why teen-agers have jumped to the top of the list for health officials, physicians and public figures promoting AIDS awareness.

Despite all the warnings about the disease, commercials about condoms and lectures about abstinence, teen-agers are the age group most likely to engage in impulsive, risky sex. They also are the least likely to realize the consequences, because the human immunodeficiency virus (HIV) has a nasty way of hiding dormant in the body for an average of 10 years before developing into full-blown AIDS and starting its deadly work.

One expert calls it “a volcano that is going to explode in the next generation.”

But the hidden risk — plus the secretive nature of most teen-age sex — has been muffling alarms.

“Kids aren’t going to change unless they see a lot of teen-agers dying,” said Dr. Evelyn Fisher, an infectious diseases specialist at Henry Ford Hospital in Detroit. “And because there’s a delay of about 10 years between infection and dying, they’re never going to see that.

“I’m very pessimistic about this.”

With good reason:

Nationally, about 20 percent of reported cases of AIDS fall among people ages 20 to 29. Since the average time span between HIV infection and the onset of AIDS is 10 years, experts believe the majority of these cases originated during teen-age years.

Among teen-agers, heterosexual transmission accounts for a higher percentage of HIV infection than it does in the general population, according to several studies. Blood tests done on applicants to the Job Corps, a program for disadvantaged youths, show that among 16- and 17-year-olds, more girls than boys are HIV-positive — the opposite of HIV infection patterns among adults.

“Nowhere in the epidemic are the dynamics changing more awfully and impressively than among adolescents,” said June Osborn, head of the National Commission on AIDS and dean of the University of Michigan School of Public Health.

“If you don’t talk to kids about sex, you risk losing them,” Fisher said. “I heard someone put it this way: You can either talk to them about sex or talk to them about living wills — you know, whether they want to be put on a respirator or other machines.

“That’s the reality. Or that’s what the reality may be in the next decade.”

Teen-agers, however, are more likely to worry about the next weekend than the next decade. And if AIDS is really such a danger, how come nobody they know is sick?

Neither Ellen, now 19, nor Brian, now 21, has outward signs of illness. Neither has been diagnosed yet with full-blown AIDS.

But both worry frequently about dying. They hope they get lucky and live to 30. It’s in God’s hands, they say. Both have become more religious since learning they have HIV.

Matthew, now 20, developed AIDS after he finished high school.

“I’m in constant pain all the time,” he said, because the disease has opened ulcers in his colon and rectum. He cannot eat most meats, most vegetables, anything fried, any uncooked fruit and all dairy products.

A typical meal is boiled chicken or a dairy-free nutritional shake.

Like Ellen and Brian, he tries to keep his condition secret from everyone but immediate family members and a few close friends. All three youths fear ostracism and harassment, so they agreed to be interviewed only if their real names were not used.

Their private agony means other teen-agers will never learn from them.

“I don’t want anyone to be afraid of me,” Brian said.

Teen-agers hear more today about AIDS, from school and television, but educators and health officials say their sexual behavior hasn’t changed much.

A national survey conducted in 1990 and released this month by the federal Centers for Disease Control found that 54 percent of high school students, grades nine-12, said they have had sex. For 12th grade alone, it was 70 percent.

The threat of HIV infection changes depending on where a teen-ager lives. The more urban an area is, the more prevalent the virus.

Random blood tests on patients at the Detroit Medical Center, deliberately excluding the highest-risk groups, found 1 in 100 people between ages 16-24 infected with HIV. In similar tests at St. Joseph Mercy Hospital hear Ann Arbor, it was 1 in 800 for all patients, with no age breakdown available.

But Detroit teen-agers with the virus are like infected teen-agers in any town — bright kids who never have used IV drugs and have had between one and six sex partners.

Dr. Paula Schuman, who estimates she has treated 20-25 teen-aged girls with HIV over the last three years at the Detroit Medical Center AIDS program, said most of them “seemed like pretty average adolescents.”

“Most of them were living with their mothers,” Schuman said. “They all wear really neat clothes. They get their hair done. They like to go shopping.

“I think it’s a big misconception that if your kid is a nice kid, he or she is safe. All of these kids are nice kids. They could be anybody’s daughters.”

Schuman sees teen-age girls who are pregnant, which is the only reason most of those with HIV find out about it. Doctors in Michigan are required to offer HIV tests to anyone who is pregnant.

Schuman wonders how many other teen-age girls are infected but have no reason or inclination to get tested. She wonders, too, about who infected them.

“Where are these men?” Schuman asked. “We never see them in here.”

In Lansing, one AIDS clinic is treating two women, both 21, for HIV infections from sexual activity during their teen-age years. Both tested positive for HIV at 18. Both grew up in the Lansing area, and one attends Michigan State University. A gay man, 25, who tested positive at age 19 after having sex partners as a youth in Lansing and Detroit also is being treated.

In an upper-middle-class suburb of Lansing two years ago, local health officials had to trace the contacts of a female high school senior who tested positive for HIV and had engaged in sex with four male classmates, plus other young men. None of the four classmates tested positive.

The tracing “was all done very quietly, but sometimes you want to scream it from the rafters — to let people know this is a risk,” said Don Sweeney, chief of school health programs for the Michigan Department of Public Health. He would not identify the suburb.

“I think the risk is small now, but the future risk is tremendous,” Sweeney said. “It smolders and it burns and if you don’t reduce it now, it’s too late.”