"The last guy I slept with gave me an infection. Nothing serious, fortunately. But . . . I haven'tslept with anyone for almost a year. Maybe I'm overreacting" -- a 33-year-old attorney.

"I've done a lot of fooling around -- slept with dozens of women -- and for me, this is a real change. I'm more cautious now and ask plenty of questions before I make my move" -- a 30-year-old advertising executive.

"Much as I don't like doing it, I put every much I meet [and am interested in] through the third degree. I still like sex and want to find a husband -- without dying in the process" -- a 29-year-old merchandise manager.

People have worried about sex since man first crawled out of the primordial swamp, but the specter of AIDS has given the subject a deadly urgency. Gay relationships have aqlready been thrown into upheaval; now, questions about heterosexual relationships are increasing.

Will people become more responsible sexually? Is an impeccable "sexual resume" the most powerful aphrodisiac? Will the one-night stand be a fling of the past? How many "urban nuns" will there be?

And, are we prepared biologically even to address these questios?

"As long as we have no treatment for AIDS," says Dr. William Masters of the Masters and Johnson Institute, "people are going to ber increasingly concerned about it -- understandably. And now that it is in the heterosexual preference group, there is going to be more furor raised."

New York research psychologist Srully Blotnick is measuring that furor.

"The sexual merry-go-round has slowed down. Women say, 'I'm defnitely being more selective, and I try to be more discriminating.' And for the first time in doing these surveys, we find men saying,'Maybe I'll forget about a willing but promiscuous partner, and go after someone whose sexual resume I can obtain."

Acquired immune deficiency syndrome cripples the body's immune system. Of the 19,181 Americans who have contracted AIDS, 10,152 are dead. Most victums are male homosexuals; intravenous users who share needles are the next largest category.

Says Dr. Harold Jaffe of the Centers for Disease Control in Atlanta: "Even if we don't see the disease radically shifting from the gay to the straight population, there's no doubt that the virus can ve sexually transmitted among heterosexual couples. It may be that transmission from men to women is more efficient than from women to men, but both are possible."

Each year since 1959, Blotnick has surveyed a total of 4,000 single, professional men and women ranging in age from 21 to 39, with a median income of $30,000 in 1986 dollars. The question, "Does concern about a sexually transmitted disease influence your decision to sleep with someone?" received a "yes" answer from 8.1 percent of the women in 1966, 11.3 in 1976 and 42.2 percent this year. For men the rates were 5.3 percent 7.2 percent and 26.4 percent.

"When we asked women what picture, event or fact they associated with their change in attitude, more than one in four volunteered the image of Rock Hudson kissing Linda Evans on 'Dynasty' without having told her he had AIDS. It became lbvious to them that men weren't being candid about their sexual and medical past."

Blotnick's conclusion of a shift in mating habits is reinforced by a number of social historians and psychologists, although they don't always agree that fear of sexual diseases is the most important reason.

David Barash, a professor of zoology and psychology at the Unviersity of Washington in Seattle, argus AIDS has produced a dilemma that highlights the collision between our slow-to-change biological systems and fast-paced cultural advancement.

"There are good biological and anthropolgical reasons," he says, "to think humans are sexually polygamous -- that they will naturally tend to seek more than one sexual partner in their lifetime. And yet monogamy has been imposed by religion and culture."

Barash, a sociobiologist who examines the biology-culture conflict in his forthcoming book The Hare and the Toroise, notes that while some people live with the restriction and stay with one secual partner their whole lives, many don't.

From a biological point of view, he speculates, having multiple sexual parners over a lifetime is an instinct that will be increasingly repressed by greater awareness of the disease. In other words, if AIDS remains unchecked, it will reinforce monogamy.

"Other things -- religion, internalized moral codes, laws -- haven't been all that inhibitory," says Barash. "But biology is the prosecutor with AIDS, and people may be more inclined to respect it."

However, matters may end up getting worse before they get better, warns Dr. John Money, director of the John Hopkins Hospital psychohormonal research unit.

"You still have a lot of people playing the personal omnipotence game. While some are becoming oriented toward this potentially fatal problem and thinking more in terms of one long-term romantic relationship, many others have a cavalier attitude of "it can't get me.' "

Money , author of The Destroying Angel: Sex, Fitness & Food in the Legacy of Degeneracy Theory, Graham Crackers, Kellogg, Corn Flakes and American Health History and other provocative studies of sexuality, makes this "rough and ready" comparison:

"There are those who go to Hartford and buy insurance and those who go to Las Vegas and gamble against the laws of chance. You can't expect all people to behave totally rationally in the face of the AIDS threat. When you decide to have sex, foten it's in a limited amount of time -- you don't pause and ruminate and think and put two and two together."

With society's increasing knowledge of the disease, "the portion of people who become cautious will increase and increase," he concedes, ''but I don't think it'' ever reach 100 percent.''

Although Gabrielle Brown's 1980 book The New Celibacy -- a pop psych text that asserted an increasing number of people were redirecting their energies -- was heavily criticized, she has turned out to be right.

According to Blotnick's surveys, 9 percent of women are now saying they're ''urban nuns,'' avoiding all new entanglements. Four percent of men say the same.

''We never got more than 2 to 3 percent of women who said that before,'' comments Blotnick. ''And the percentage of men was always less than one-half of 1 percent. It's striking to hear healthy adults in their prime years saying they won't bed down with someone they're attracted to, because they're afraid the person has too long a 'sexual resume.' ''

But even if fear of AIDS has caused an increase in abstinence, Brown doesn't consider her thesis vindicated. ''That's celibacy by default as opposed to by choice. If you're celibate because you're afraid of getting ill, that's not expansive. It's scary and lonely -- especially if you have no good reason to be worried.''

Brown also resists the urge to entirely ascribe the shift in behavior to the threat of sexual diseases. ''We were already going in the direction of more responsible relationships. The era of the one-night stand was over. It's unfair to use AIDS and herpes as a reason why people will be more careful. People are more intelligent than that, and more sensitive.''

The only positive result of a fear-based concern about sex, she says, would be if it led to a deeper understanding of the possibilities implicit in a relationship. ''Any time a door closes and people think they're going to lose something, another door opens and gives them even more freedom.

''Rather than focus on sexual encounters of the one-night variety, people will start focusing on long-term relationships,'' she adds. ''Instead of thinking, 'I wonder who I could sleep with tonight,' you ask, 'I wonder who I could love.' Your heart will expand.''

Fear of AIDS, futurist Isaac Asimov agrees, will have little effect on heterosexual relationships.

''We can judge the future from the past,'' he says. ''It seems to me that for a long time people have been saying that extramarital sex will send you to hell -- and people have indulged in it anyway. For a long time people have been afraid of gonorrhea and syphllis -- and people have indulged in sex anyway. AIDS won't stop sex. Nothing else ever has.''

And, adds Asimov, fear of the disease won't make a difference: Even if a cure isn't found, ''people will continue to take their chances, as they always have.''

Actually, says historian Ellen Rothman, people haven't always taken their chances. And more often than not, they didn't because the risks were simply too high.

''AIDS is something unto itself because it's a matter of life and death, but for a long time there was a great deal of danger associated with pre-marital sex -- and now it's becoming dangerous again," says Rothman, a visiting scholar at the Wellesley College Center for Research on Women and author of Hands and Hearts: A History of Courtship in America.

"We finally managed to separate sex from reproduction -- only to find an intimate connection between sex and disease," she says. "These diseases make sex dangerous again, something that hasn't happened since the 1920's. Before that, sex was associated with the risk of pregnancy and childbearing."

And while AIDS may be an anomaly in the history of courtship, it resonates, she says, to the Sexual Purity crusaders, who were strong in the 1830s and from 1875 to 1915. The movement, which closed red light districts, was led by reformers concerned about the sexual double standard: it was okay for men to be experienced sexually, but women had to be virgins.

"When a young woman was about to marry, a family influenced by the movement undertook to find out whether the finace was sexually pure and free from veneral disease. Now, young men and women are again starting to scrutinize the sexual history of anyone they might sleep with -- no longer for moral reasons, but for medical reasons, so you know what risks you're running."

Those risks, according to Blotnick, are much more closely evaluated today than in the past. When asked, "In the past three months, have you had sex with someone you didn't love?", 43.3 percent of his female suvery respondents said "yes" in 1966; 37.1 in 1976; and 27.9 in '86. For males, the rate rose slightly from 72.6 percent in '66 to 74.1 percent in '76, and then fell sharply to 48 percent this year.

"In both groups it was sloping down before," says Blotnick. "Now it's suddenly bent down, with much of the decrease in the past two years."

If AIDS continues unabated, "common sense would tell yo that the one-night stand would become limited to the more venturesome of self-destructive people," says Rothman. Weighing against this, however, is that "young people have no sense of their own mortality. If you think you can drive drunk and not get hurt, you'll think you can sleep around and not get AIDS."

Meanwhile, concern over AIDS is making many men almost as cautious as many women have always been.

"Females of many species tend to be relatively coy comparison shoppers, whereas males, by and large, tend to be aggressive sexual advertisers," says zoologist Barash. "This is partly because the consequences -- pregnancy -- for any sexual encounters fall more heavily on the female."

Now, because men must face potentially deadly consequences from sex, he predicts they "will become more 'female-like' and discrimminating in their sexual strategies."

Women, says Blotnick, are becoming more like men in a different sense: They are responding to the risk of sexual disease by buying more condoms. His surveys chart the percentage of condoms being sold to women at between 30 and 40 percent.

"It isn't just gays practicing safe sex, it's single heterosexuals too," he says. "In the '50s, if, with an Ozzie and Harriet-type couple, he told her to pick up some condoms, she'd have thrown a frozen TV dinner at him. But now the women are buying them without being told -- as a precaution."

In an uncertain time, sexual diseases may be providing a situation that biology has not prepared us for.

"If you look at primitive man," says Barash, "human beings encountered few people -- which meant few potential sexual encounters. Now, you rub shoulders each day with literally hundreds or thousands of strangers."

The abundance of advertising, which presents images of society's most alluring members, offers a further conflict. "We are constantly exposed to sexual stimuli, both qualitatively and quantitatively. The disparity between culture and biology offers a built-in potential for sexual confusion and over-stumulation."

With AIDS, on the one hand we have a situation in which our sexual inclinations are very much stimulated by culture, "but now "but now suddenly we're being told that they could kill you, too. It's a classic mixed message."

Trust or lust?

Issues of trust run through the history of courtship and marriage, historian Rothman notes, and she predicts they're going to become even more highly charged.

Before the 19th century, a woman would ask a potential husband if he had enough land and livestock, if he could make his family comfortable. A man would ask a potential wife if she had the skills to make good butter, or knew how to spin wool. Both sexes relied on ministers, officials and parcents to guide their choice of a mate.

"It was much more concrete then. But by 1800, people began looking to their own feelings to lead them to a loving and secure marriage. Trust and candor became very important, and they've never gone away," she says.

"If AIDS is not brought under control, instead of needing trust and commitment for marriage, they'll be required at a much earlier stage -- as soon as sexual intimacy becomes an issue."

Another emerging consequence, says Blotnick, is a rise in romances among people who already know one another, as singles seek safety in familiarity.

"Someone in a bar may not tell the truth, but in a less pressured setting, there's not as much reason to lie. You can check someone out much more easily at work. 'Have you been seeing anyone lately?' comes up in normal conversation."

If this sounds a little reminiscent of high school, that's because the dating secene of the future may look less like a singles bar and more like the sophomore hop.

"One nice thing about high school is that you can easily get the inside scoop on someone you're interested in", says Blotnick. "You can get other people's judgment. In the past, that was about looks and popularity. Now it will be about the person's sexual habits and their honesty.

"And just like in high school, things will happen slower. Once again, sexual relationships will be a matter of biding your time."