"IT WASN'T JUST sex. We were really involved with each other. I developed so much self-confidence from that relationship. I feel very comfortable about sex now. That relationship was one of the most important things in my growing up."

As I listened to the bright, accomplished young woman, a student at T. C. Williams High School in Alexandria, I felt as though I were listening to a single or divorced woman in her thirties casually talking about a recent affair. But in the back of my mind I kept hearing the voice of Msgr. Herlihy, the principal of the Catholic high school I attended. "Mortal sin! Mortal sin !" he whispered.

I couldn't resist asking my student: "Don't you regret not waiting? Don't you think that this guy has used you? Don't you feel any guilt?" She replied that people my age don't realize how much a long-term relationship can mean to a teen-ager.

To be honest, I don't. Attitudes toward sex were just too different when I was a student at Notre Dame High School in Batavia, N.Y., in the mid-'50s. Maybe my high-school experience was unusually repressive, even for the '50s. And granted, it's not easy for a 46-year-old English teacher to get a clear reading on just what is going on with kids. Still, I believe that the majority of my generation has difficulty understanding and coming to terms with theradically different sexual attitudes and habits of this generation of high-school students.

Most of the recent public discussion of teen-age sex has dealt with pregnancy among low-income students and its relationship to the cycle of poverty. But we often overlook the revolution in sexual attitudes -- and the apparently ever-increasing amount of sexual activity -- among middle- and upper-income kids.

"There's a feeling that it's okay for us to have sex because we're educated and know what's going on. We're not going to get pregnant and burden society with unwanted children. We're going to college and have a future. If we do slip up, we'll get an abortion," says one sexually active honors student.

When, in the course of getting material for this article, I first heard remarks like this, I thought that the kids were hiding something -- that deep down they were feeling terribly guilty. (Guilt was a very familiar emotion when I was growing up. I remember a compulsory retreat in my senior year during which a Jesuit priest, imported from Buffalo, preached for two days that "french kissing" and "deliberately entertaining impure thoughts" would lead to eternal damnation.) But I soon came to realize that I was reading my '50s attitudes about sex into these kids, and in fact that most of them may feel little if any guilt. "A lot of kids believe in God but just don't think God disapproves of their sex lives," says senior Will Peyton, a National Merit semi-finalist.

The general feeling among scores of middle-class kids I talked to is that as long as high-school couples are "going together" and are faithful to each other -- even if the relationship lasts only a few months -- sexual intercourse is fine. Even among those kids who are not sexually active there seems to be an amazingly tolerant and casual attitude towards friends who are. As school psychologist Roberta New says, "If sex is in the context of a serious relationship, they think it's perfectly natural. Even kids who have 'serially monogamous' relationships -- two or three affairs a year -- seem to feel little guilt. The sexual liberation that college students began experiencing in the '60s is now full-blown in high-school. The only difference is that high-school students still have parents around and have to be sneaky about it."

Said one high-achieving student at T. C. Williams: "I remember once when my mother suggested that it might be time for me to have my first gynecological exam. I told her that I didn't really need to see a gynecologist now. What I didn't tell her is that I had been seeing one to get birth-control pills already. I felt like my mother was probing to find out if I was sexually active. It made me uncomfortable."

Among the kids there is some disagreement as to just how much their parents do know about what's going on. "Parents are only around their own kids, and their own kids deceive them. I've one friend who has had 10 big parties in her house in the last year, and her parents, who've been out of town during each of them, have no idea about it. If they can't even find out about wild parties, how can they be expected to find out about their kid's private sex life?" says a top student. Senior Will Peyton thinks that parents may know more than they let on. "Most parents suspect what's going on, and many are even sure, but very few dare confront their kid," he says.

When it comes to confrontations about sex, it often seems that the "children" have the upper hand. "It's hilarious to watch my mother try to find out about my sex life. I've grown up with all these messages about being open -- the 'You can tell me anything, dear -- I'm from the '60s' kind of stuff. She's had the 'Joy of Sex' on the living-room bookshelf since I've been in sixth grade. But now that I'm 17 and have a boyfriend she's getting desperate to know what's going on," says one of my favorite students who admitted that in fact she isn't sexually active but doesn't think it's her mother's business either way.

Another girl sees that same desperation in her mother: "My parents . . . never punished me unfairly. But now that I'm serious about a guy, my mother is a different person. She makes all these nervous asides -- 'Now, don't jump into things, dear' -- hoping she's getting her points across. But I really feel that it's none of her business. How can sex be personal and intimate if you go tell your mom about it? She doesn't tell me about her sex life," says this frank, charming and high-achieving student.

Kids seem to agree that the idea of "modern" parents being so open with their children is a gigantic myth. "The only kind of open discussion that parents want is one that ends with 'Gee, mom and dad, you're so right and I'm not sexually active and won't be at least till I get out of high school,' " says one 16-year-old boy.

Most kids say that their friends are bigger sources of psychological support than their parents. "Friends listen and understand. But most parents can't help being judgmental," says one student. "And just because you don't go around confiding the intimate details of your life to your parents, it doesn't mean that you have a bad relationship with them." Says another: "If parents haven't given their kids the right values by the time they are 13, it's too late. The kids will find a way to sneak out and do what they want."

It's especially hard for divorced parents, who may be having affairs themselves, to give the "right values" to their teen-agers. "When your mother has a Friday night date and he's in the kitchen eating breakfast Saturday morning, how can she preach about premarital sex?" says one student.

Jean Hunter, director of the family-life program in the Alexandria schools and a recognized expert on adolescent sexuality, is concerned about what she sees as a tacit complicity going on between parents and their teen-agers. "Many parents agree to pretend that their kids are not sexually active and in return the kids pretend for the parents' sake that they aren't," says Hunter. When these kids get pregnant and take the usual middle-class solution -- abortion -- they end up counseling themselves without the support of parents. Hunter feels that parents and other adults can no longer afford to ignore the increasing sexual activity among teens because of the growing risks of AIDS.

AIDS may have changed the sexual practices of single adults in Georgetown bars, but high-school kids seem to act as if they are totally immune to the disease. The preferred method of birth control among middle-class high-school couples is the pill. Students say that no girl on the pill is going to ask her boyfriend to use a condom just to be safe about AIDS. "It would be insulting to the guys, implying that they were cheating on you or were bisexuals," one senior girl says. Another says that "it would break the mood" to ask a boy to wear a condom.

The main illusion that so many of these seemingly sophisticated kids have is that high school is one big family whose members have known each other since kindergarten. They tend to forget that some of that family are having outside sexual contacts on weekends, at college and on vacations. "High-school girls are very naive about what their older boyfriends are doing in college. Most of the guys I know are very sexually active in college and then come home and sleep with their old girlfriends and pretend that they've been faithful. Those girls are taking big chances," says Kellie Ray, now a college freshman. There was a case recently in my school where an old boyfriend infected one of our girls with a sexually-transmitted disease that he had picked up in college.

Jim Dawes, the valedictorian of T.C.'s class of '87, says that for many kids "AIDS is kind of like nuclear war. It's too big to worry about." And the long latency period of the disease means that few students will show symptoms while still in high school. However, various school personnel recently heard that two former students were infected with the AIDS virus. But when the report surfaced at a recent hearing, it was discounted by city health and school officials.

There is still considerable reluctance on the part of high schools to face up to the prevalence of sexual activities and the associated risks. But as soon as a kid enters college, he or she is bombarded with warnings about AIDS and other diseases. At Amherst College, for example, a student group puts condoms and informational packets with red crosses on them in student mailboxes. A former student of mine said she recently went to a "safe-sex" party at Amherst where, in order to get a beer, a partygoer had to display a condom. At Vassar a pink machine in the laundry room dispenses condoms.

But with all the openess about sex these days, it's easy to overlook the fact that a great number of kids still don't do it. There are really more virgins, male and female, in our high schools and colleges than generally assumed. Studies show that when students are asked what percentage of their classmates they think are sexually active the numbers run as high as 80 percent. When individual students are asked if they are sexually active, however, the figure drops to around 50 percent, about the same rate that a 1986 Harris poll showed for 17-year-olds.

My students say it's not really "in" to come out and say you're a virgin. Recently, when I was talking to several kids to get ideas for this article, none of them said that they were sexually active -- yet the impressions they seemed to leave with me and with each other was that they were. One of them returned later to tell me privately that she was a virgin but just felt funny saying so in front of the others.

Gary Alward says flat out that he doesn't believe in sex before marriage. He and his tall, attractive blond girlfriend, Katherine Reilly, have been dating each other exclusively for almost three years. Gary says his belief in abstinence comes from his Baptist faith. Katherine, a Catholic, says: "I just don't feel ready for sex now. One of the reasons that Gary and I have such a good relationship is that he doesn't pressure me."

Family-life teacher Jean Hunter says that adults have to help more kids to realize what Katherine and Gary have discovered: It's difficult but possible to have a meaningful, intimate relationship without sex. One thing that may make it easier for Katherine and Gary is that they are part of a group of about 20 kids, few of whom are paired off as couples. What the group members seem to have in common are high academic achievement, intelligence and a wide variety of interests. I am told that it is not "in" with these kids to be sexually active, although they seem tolerant of friends who are.

There are many bright kids at T.C. who are not part of this group. There are also many other kids not in the group who are not sexually active. But other indicators suggest some relationship between academic achievement and virginity. A recent poll of 1,985 students who appear in "Who's Who Among High School Students" claims that only 26 percent of the males and 24 percent of the females surveyed say they have lost their virginity; those figures are well below the commonly accepted figures of 50 percent for all teens. But Will Peyton isn't sure: "There might be a marginal difference between the groups, but the real difference is that the high-achievers are just more discreet about sex," says Peyton. One very bright, sexually active girl says that with some of her high achieving friends virginity is less a matter of morality than of time. "Some of them are just too busy with school work to form the kind of personal relationship that would lead to sex. Given enough time and the right person, they might change their minds fast."

(Certainly the priests and nuns I had in high school understood the time factor. Keeping busy was the saltpeter of my generation. Young men were constantly encouraged to get into every kind of sport and other activity. The priests called it "avoiding temptation;" Freud called it sublimation.)

There may be argument about the correlation between academic achievement and virginity, but there's almost universal agreement that drinking goes hand in hand with teen-age sex. Almost every kid I talked to says that students who drink a lot tend to be more sexually active -- and more promiscuous -- than those who do not. "I've seen couples who hardly know each other start drinking at a party and get so carried away they'll slip off somewhere and have sex. Sometimes it's really funny to see these girls who act like such prudes at school start coming on to guys after they had a few drinks," says one party observer.

As I look back on the vitriolic discussions I was part of as a member of the Alexandria Mayor's Task Force studying the proposed school-based health clinic at T.C., it seems that many adults on both sides, myself included, had no clear understanding of teen-age sex today. Those against the clinic described kids who have sex as "bad," or "corrupted." One elderly gentleman told the City Council that a clinic that dispensed condoms would turn our youth into "rubberized rabbits." A local pastor predicted that "our historic city would become a Sodom and Gomorrah." My side, the pro-clinic forces, didn't seem any more on target. The working assumption seemed to be that kids just couldn't control themselves and needed institutional intervention to protect them from pregnancy or sexually transmitted diseases.

Few of us adults seem able or willing to understand that there are some extraordinarily mature teen-agers who make informed decisions to have sexual intercourse with someone they care deeply about. I wonder how adults on my task force would react to the discussion that I described in the first paragraph of this article. Here was a highly respected and intelligent student -- a girl I would be proud to have as my daughter -- telling me that her long relationship with a fellow student had given her self-confidence and the deep enjoyment of a caring relationship. "I don't have a single regret about it," she concluded.

From other kids I've talked to, I don't think that her situation is that unusual. Another innocent looking, charming young woman, also a top student, had very similar attitudes about her sexual activity. "When I was in 10th grade, I slept with a boy for the first time, but the relationship only lasted a few months. I think I was naive and expected too much. With my next boyfriend everything worked out great. After several dates we started sleeping together and it lasted for eight months. Those eight months were the best time of my life. I wouldn't trade them for anything. Even though we don't date anymore, we're still very close. I feel that no one knows me better than him."

What we may be seeing in the attitudes of these young women is not Sodom and Gomorrah revisited but an attempt to formulate an ethical code that judges sex in terms of individual personal relationships instead of absolute religious and moral codes. The students' ethics condemns promiscuity as degrading, but approves of sex between teen-agers committed to each other. Even many teen-agers who come from staunch Catholic homes say that the church's strict teaching on premarital sex has little relevance. "Our parents' beliefs about sex and religion just don't carry over to too many of us. Most kids make their decision based on their own conscience and on how committed to the other person they are," says a 16-year-old member of a local parish.

I'd be dishonest not to admit that a part of me feels my students ought to be guilt-stricken -- or at least a little repentant -- about their sexual attitudes and experiences. But another part of me recalls that teen-agers in the '40s and '50s weren't as pure as we would like to remember. Granted, more kids today slip off to their parents' empty homes for afternoon trysts than ever did back then. (Back seats of cars are now viewed as "not very classy" venues for sex.) But teen-age childbearing rates peaked in the '50s along with shotgun marriages. In those days many kids dropped out of high school, went to work and got married, while many others married soon after graduation. Early marriages took care of many of the raging hormones of those times, but they often ended in early divorces -- the source of so much turmoil in the lives of today's young people.

Is it surprising that this generation is forging its own moral code? Many more young people than ever before are encouraged to go on to college, postpone marriage for many years and at the same time not be sexually active. As psychologist Bruno Bettelheim observes, "This expectation cannot help creating severe emotional strains in the young, problems in their relations to each other, and difficulties in their relations to their parents." Looked at in that perspective, perhaps we should be thankful that students are as responsible, and as well-adjusted, as so many seem to be.

Patrick Welsh has taught English at T.C. Williams High School in Alexandia for 17 years. He is the author of "Tales Out of School."