Teen sex isn't what it used to be. Federal officials say more than half the high-school students they asked are abstaining - and most of the ones who are having sex are using condoms.

It is the first time this decade that more than half of America's high school students are saying no to sex, the Centers for Disease Control and Prevention said Thursday. And high-schoolers who are sexually active are using condoms at the highest rate recorded in the 1990s.Dr. Lloyd Kolbe, director of the CDC's Division of Adolescent and School Health, and others said the findings show that teaching teenagers about safe sex hasn't resulted in more promiscuity.

"I've never believed giving a kid access to a condom is going to promote sexual activity. Now we have evidence that this is correct," said Daniel Zingale, executive director of AIDS Action, a Washington-based advocacy group.

Kolbe also said the findings show that teens who are virgins shouldn't feel like outcasts.

"It's an important milestone because students who have not engaged in intercourse can say that they're in the majority," he said.

The 1997 survey of 16,262 students nationwide showed that a lower proportion of high schoolers are engaging in risky sexual behavior than in 1991, when the CDC began giving teenagers anonymous questionnaires every two years about their sex lives.

Asked if they had ever had sexual intercourse, 52 percent of those surveyed last year said no, compared with 46 percent in 1991. Asked if they used a condom the last time they had sex, 57 percent of students said yes, compared with 46 percent in 1991.

Sixteen percent of students said they had had sex with four or more partners, down from 19 percent in 1991.

The trend toward abstinence in the 1990s is in sharp contrast to the 1970s and '80s, when sexual activity ballooned among teenagers, Kolbe said. Sexual activity among girls 15 to 19, for example, jumped from 29 percent in 1970 to 57 percent in 1988, according to previous studies.

Kolbe attributed the recent declines to efforts by parents, schools and health officials to educate young people about safe sex and the risks of teen pregnancy, AIDS and other sexually transmitted diseases.

But he warned there are still plenty of conflicting sexual messages in movies, television and other media.

"I think they're fragile changes," he said. "The worst thing we could do is be lulled into complacency."