The sexual revolution may not be over, but things sure have changed. The deadly acquired immune deficiency syndrome (AIDS) and the prevalence of other sexually transmitted diseases such as herpes and gonorrhea have altered the game of recreational sex and slowed the initial sexual pace of potentially more serious relationships, say medical and behavioral experts.

"Concern over contracting a sexually transmitted disease for which there is no cure and has a high mortality rate [AIDS] is an inhibiting situation in itself," said Dr. Louise Tyrer, vice president for medical affairs of the Planned Parenthood Federation of America.

"People are being far more careful -- the stakes are too high," added Dr. Michael Quadland, associate professor of psychiatry at Mount Sinai Medical Center in New York and a therapist in private practice. "People want to know about their partner's sexual behavior outside their own relationship. They are asking questions far more frankly than in the past. If you are dating, it's not unusual to want to know about your partner's sexual history. That used to be considered uptight and tasteless."

While studies show that homosexuals are becoming increasingly monogamous, and sometimes celibate, in reaction to concern about AIDS, there is no comparable research on heterosexual behavior. Yet anecdotal evidence leads sex therapists to report that one-night stands appear to be decreasing and that people are more wary of extramarital affairs and relationships with new partners.

But whether patients' reports of such reduced sexual activity accurately reflect behavior is "an unanswered question," said Shirley Zussman, codirector of the Association for Male Sexual Dysfunction and former president of the American Association of Sex Educators, Counselors and Therapists.

What is clearer, she said, is that one-night stands are probably much less frequent and couples are approaching sexual aspects of new relationships much more slowly. "People are somewhat apprehensive about going to bed with someone they have met the night before or that night," said Zussman, a Manhattan sex therapist. "There is some anxiety over casual sex with a partner with whom they have very little expectation of being involved with more than a couple of times."

Caution and fear of sexually transmitted disease -- rather than a changing and more conservative morality -- are probably the overriding reasons, Zussman and other sex experts said. "Sexually transmitted diseases don't give rise to true changes in moralities, although they could have an inhibiting effect on sexual behavior," said Donald L. Mosher, professor of psychology who has done research in sex guilt at the University of Connecticut.

Fear of sexually transmitted diseases edged war and peace as the subject most American women were concerned about in 1985, according to a national study of women's attitudes commissioned by Glamour magazine. When asked to cite those subjects that they worried about more in 1985 than the year before, 70 percent of the respondents cited sexually transmitted diseases, 69 percent cited war and peace (which was the number one concern in 1984) and 65 percent said personal health.

In addition to changing people's attitudes, there's no doubt that sexually transmitted diseases -- AIDS, herpes, gonorrhea, syphilis and the recently recognized chlamydia -- are changing the sexual climate in America. Some examples:

*Male dancers who entertain women at the Pulsations and Chippendales clubs in New York, Philadelphia and Los Angeles gargle with antibacterial products before and after their performances, which include kissing women. Open-mouth kissing is prohibited.

*A New York therapist said a client told him that he hadn't had sex in two years so he "didn't have to think about dying."

*A "social card" that can be screened by a new sex partner is being sold at a Denver health clinic. It lists results of tests for sexually transmitted diseases.

Concern is particularly great among young adults who, traditionally, are more likely to be sexually active with more than one partner, experts said.

"AIDS and herpes come up daily in conversations," said a recent Temple University graduate. In some college human sexuality classes, fear of herpes -- which was the most feared sexually transmitted disease in the early 1980s -- is already passe.

At Syracuse University, psychology professor Clive Davis conducted a three-part lecture series on human sexuality in October to 1,400 students and subsequently met with all of them in small groups. "The only questions related to sexually transmitted diseases were about AIDS," said Davis, who is president of the national Society for the Scientific Study of Sex and is studying the herpes virus.

In the sexually transmitted diseases discussion in his human sexuality course at American University this fall, "the only thing students wanted to hear about was AIDS," said Barry McCarthy, a clinical psychologist and sex therapist at the Washington Psychological Center, who teaches at AU. "That's an interesting myth, because gonorrhea and herpes are a much greater reality."

Fear of AIDS apparently has reduced the fear and stigma of other sexually transmitted diseases, which infect many more people.

"Syphilis and gonorrhea, you know you can get rid of them with a couple doses of penicillin," said a South Florida woman in her mid-thirties. "But AIDS, my God, you can die."

"Two years ago I felt terrible for people who had herpes," said a New York writer who recently discovered some genital warts. "When I saw these bumps, you know I didn't care. AIDS has made other forms of veneral diseases unimportant."

Some forms of sexually transmitted disease are actually on the decline. The rates and gonorrhea and syphilis have been dropping nationwide for several years -- a result, experts say, of health programs to combat the diseases as well as decreased, or more careful, sexual activity spurred by fear of herpes and AIDS.

Gonorrhea peaked in 1978 with 1.01 million cases reported to the federal Centers for Disease Control in Atlanta. Since then, the incidence has steadily declined to 878,556 in 1984, the last available total.

Syphilis peaked in 1982 with 33,698 cases, but had dropped to 28,607 reported cases in 1984. About half of the 1984 syphillis cases were in homosexuals.

CDC statistician Joe Blount credits the decline of gonorrhea primarily to a nationwide medical and educational control program instituted in the early 1970s. Syphilis is falling for the same reason as well as from the fear of AIDS and herpes, he said.

Doctors are not required to report herpes and chlamydia, so no figures are available, although their prevalence is growing, Blount said.

While concern about sexually transmitted diseases is cited as a major reason for recent shifts away from instant sexual relationships, some experts said that this is only partly responsible for new sexual attitudes.

"There's some disenchantment with the promiscuous life style," said psychiatrist Quadland of Mt. Sinai hospital. "We had to go through the '60s and '70s, where people, especially gays and women, could express themselves as freely as they wanted to, but there are some costs to that. Now the general behavior is toward seeing sex as most satisfying in a committed relationship."

"People are moving to a slightly more conservative stance about how sexually active they are, especially with relative strangers," said Dr. Martin Goldberg, director of the Marriage Council of Philadelphia and director of family study at the University of Pennsylvania. Longer courtships are in vogue, he said, for a variety of reasons including the more conservative sociopolitical atmosphere and concern about sexually transmitted diseases.

"Psychologically, people have learned that quick physical intimacy does not establish real psychological intimacy, and is sometimes harmful to intimacy and can abort what might be a promising relationship," he said. This notion is most prominent among adults 21 to 35, Goldberg said, many of whom are divorced or separated and had once "thought there was no reason not to have sex immediately with someone you meet."

As for sexual diseases, "most people are taking the attitude that the more they can minimize the number of people with whom they have sexual contacts, the less risk," he said.

Women in particular are discriminating between casual sex and relationships that might develop into something long term, said New York therapist Zussman. But "there doesn't seem to be any avoidance of a sexual relationship once people get to know each other," she said. Except for the occasional case, "people aren't abstaining. There isn't a new celibacy."

Others agree.

"Although some investigators are beginning to report somewhat larger percentages of virgins among college students, from what I see on my own campus, I'm not convinced of that," said psychologist Mosher at the University of Connecticut.

"In the back of their minds people may have an apprehension," said Zussman, "but they somehow trust that their judgment in the sex partner they've chosen is sufficiently good. They aren't letting that apprehension interfere with having a sexual relationship when the expectation is that it will be ongoing."

That attitude may make the one-night stand far less popular, she said, but it doesn't get in the way of married individuals inclined to indulge in the "old-fashion 'affair.' "

"It's as if there are so many barriers and anxieties about forming relationships that people decide they can't cope with another problem, another anxiety that goes along with finding a partner," she said. So they go on and have their affairs anyway -- once they're relatively sure it's safe, she said. "I don't think fears of sexual diseases prevent people from involving themselves in a sexual relationship once they have a great deal of trust or confidence."

Some experts argue that reports of changing sexual behavior through fear of sexually transmitted disease have little basis in fact. "About 1983, a dramatic change in the behavior of sexually active young people was reported because of their fear of catching herpes," noted herpes researcher Davis from Syracuse University. "The little research that was done by me and others did not suggest that that was the case. Some people did change, but the amount of change was not dramatic. Most people retained their dating patterns, and even those who were diagnosed with AIDS as well actually changed less than the anecdotal accounts indicated."

Davis points to people's reluctance to use contraception as a parallel. Statistically, 80 percent of young men and 70 percent of young women engage in intercourse at least once by the age of 19, he said, yet only about one third of them use contraception consistently.

"The fact that most of them know that pregnancy is possible," he said, "does not change their practices." Applying the same pattern of denial to sexually transmitted diseases -- "my partner doesn't have anything" -- means it's reasonable to assume that there will be little change in sexual behavior, he said.

What is clear, however, is the existence of a growing but irrational "AIDS hysteria" -- the fear of having contracted the deadly disease from long-ago relationships, restaurants, door knobs and handshakes, several clinicians said. That reaction is typical when a new, widespread disease occurs, they said.

"We're certainly seeing a lot of people who are anxious anyway and believe themselves to be at risk," said Dr. Dolph Druckman, a research fellow at the division of infectious diseases at Johns Hopkins University Hospital. But, Davis said, "it will be some time," if at all, before any statistically recognizable change occurs throughout the population.