Sex sparks ecstasy, madness, poetry and more silliness than the human animal should have to bear, but these were not the main topics of concern at the 13th National Sex Institute sponsored by the American Association of Sex Educators, Counselors and Therapists.

They were in town, in fact, for five days to discuss weighty issues, to address the theme of "Challenges to Sexology in the '80s: Forward and Backward"; to avoid double entendre whenever possible, and to take their topic very seriously.

All of this they accomplished, while taking comfort in the fact that theirs was a subject not likely to lose its relevance even in this flighty age of trends and cults and ideologies with lives as long as a mayfly's. As one conference participant put it, "The thing about sex is, it does have survival value as far as the species is concerned."

"My hands were so wet, my body was trembling, I just had to lie there and let my body recover." This is Nancy Friday talking about the ordeal of writing "My Secret Garden," her book about women's sexual fantasies. Those difficulties, however, were nothing compared to what it was like writing her latest book, on men's sexual fantasies.

"I never felt like a bad woman writing about women's fantasies," she said in a speech to the assembled participants. "But doing men's fantasies, I felt like it was dirty. It was bizaar! I couldn't understand it!" said Friday, who was much given to talking in italics and exclamation points.

All in all, it was a nostalgic sort of speech, the kind of call to the sexual barricades delivered in the same tone that used to be heard from the steps of freshly seized univerisity buildings. Friday exhorted the women to stop making their love so conditional, thereby confusing their poor male partners.

"After all," she asked indignantly, "has a women ever had to beg a man for sex?"

In the audience, puzzled looks were exchanged. "Sure," said one impeccably tailored young woman. "Lots of times. What's she talking about?"

In the end, the author had a question to ask her audience. "Tell me, do you think this kind of talk is too much? I mean, is the world ready for oral sex? I do think it is the kiss of life. Do you think it would sell on the 'Merv Griffin Show'?"

In between panels, Patricia Shiller, looking comfortable and dowager-like in sensible shoes and a cardigan sweater, was noting the changes, as befits the founder of a 13-year-old organization, and counting the three-piece suits. "Lots more of them this year," she said. "It used to be that everyone wore blue jeans and open shifts and sat on the floor."

The issues were changing with the clothes sytles, it seemed. There was the growing threat that sex educators were facing from fundamentalist religious groups and right-wing politicians, and there was a different focus in the kind of problems that parents were bringing to sex therapists. "There are fewer people coming in and saying 'I don't have orgasms,'" Shiller said. "There is more emphasis on working with the aged and the physically disabled."

The trend has also turned away from sexual acrobatics as the major ingredient of a happy sex life, Shiller said. "People used to think that being a sexual athlete or bed-hopping or whatever would make sex better. But basically, human beings want intimacy and trust within a relationship, not just different positions."

Still, what with all the variations on the basic theme that have flowered over the last decade or two, Shiller said that she was the one with "the alternate life style. I've been married 38 years to the same man and lived in the same house for 30 years," she said. "I'm really a minority."

Some of the most interesting conversation took place outside of the formal sessions. As the subject of "Homosexuality of Coping with Stress" burned brightly within the walls of the Presidential Ballroom of the Capitol Hilton, outside in the hall two conferees were locked in great debate.

"This woman," said a young woman from behind her horn-rimmed glasses, "told me that she has fewer orgasms and is getting more out of sex. Now how do you explain that? I just can't buy it."

"Oh, I can see where it might be possible, " said her companion. "This society has gotten so orgasm-obsessed, it's outrageous."

"Of course, you would say that, you're probably still into Masters and Johnson," the first woman said indignantly. "Oh, God, I get so worked up about this."

The big news at this year's conference was the possibility that there might actually be such a phenomenon as female ejaculation. "If it's true, it would have revolutionary implications, said William R. Stayton.

Stayton is a mild, unassuming sex counselor who is also a Baptist doctor of theology. He wears an air of such total unflappability that he gives the impression you couldn't disconcert him even if you walked into his office and announced your determination to have a joyous, open, caring relationship with an oil derrick.

Stayton says there have definitely been shifts in the kinds of problems he's been seeing these days. "There's a lot of cases of inhibited sexual desire," he says. "A lot more of that, unbelievable." The principal victims apparently are men who, having become understandably confused over what role they are supposed to assume in a relationship these days, have hung a permanent out-to-lunch sign on their libidos.

"The other thing I'm finding is bisexual married couples, I must have had a dozen cases in the last year. I help integrate the two interests. It used to be if a man had a homosexual desire he would end the marriage. Now he's having both. There's been a real breakdown of sex-role stereo-types. We've gone through a period of evolution. Fifteen years ago, we talked about sexual perversion. Ten years ago, it was variation, and now we refer to erotic minorities."

Like any group of professionals, the members of AASECT have developed their own patois with which to converse and to seal their solidarity. There is lots of talk about SAR's (sexual attitude restructuring), MO girls (multiple orgasm) and M and J (Masters and Johnson). Relationships are to be "open, loving, joyous and caring" or any combination thereof. There are no third-rate romances in sex-therapy talk. Low-rent rendezvous are out, out, out. Not to mention giggles, blushes or any suggestion this is not very serious business. Which of course it is.

Sample sex history (short form) on display: "How do you feel about being a woman (man)? How do you feel about the opposite sex? How do you feel about your body? How do you feel that your partner feels about your body?"

Walking down the hall with statuesque grace is Ariadne Kane, who is dressed in a black velvet suit with a straight skirt, high heels, gold earrings, impeccable hair and makeup and who is, at second glance, a man. Not a transvestite; the word is considered pejorative. Ariadne Kane is a cross-dresser, a sex educator who specializes in "issues of gender." Married eight years, living outside of Boston, Kane's main interest is his annual Fantasia Fair, "a unique opportunity to explore the practical aspects of cross-dressing and its attendant alternative-gender live styles." At the conference, however, his main interest is in "trying to get more understanding so that people can appreciate this aspect of human behavior."

It isn't as easy job. "I'm really a voice crying out in the wilderness," Kane says. While the women at the conference have been "just fabulous" about talking with him on the issue, not everyone was so understanding. A lot of people would rather avoid the issue than confront it, Kane said. "At this point I feel more and more like I'm neither a man nor a woman. I'm a creature from outer space. Sometimes, it can get very spaced out."

No, no, no, said the sex educators at the dutch-treat cocktail party that preceded the four-hour film festival. One does not get the least bit excited watching these movies. The festival would include all manner of more-or-less, usually more, explicit films dealing with everything from "a brief but delightful one person sexual interlude. No voice overlay; just music and sounds of excitation" (aka female masturbation), to the trials of puberty. It's all very clinical, really. After all, as Mary Beth Yakoubian observed with just the right degree of cool detachment, "After you've seen a million masturbation movies, you've simply trying to find out if a better one's been made."

This point of view simply did not ring true with Jeffrey E. Cosnow, anthropologist. "You have all these highly educated types sitting around watching these movies and taking notes, and this woman comes on the screen with these phenomenally sized . . ." Cosnow was momentarily at a loss for words. "Anyway, I don't understand why I was the only one there saying 'Wow!'"

There followed much urgent discussion about the difference between sex and sexuality and getting in touch with one's feelings, but Cosnow was unconvinced. "You people talk about feelings a lot and getting in touch with them but there's a very strict definition of what that means. I think there's a lot of denial going on here," he concluded rather ominously.

The movies began, movies on lesbianism, on romance and sex and marriage, and no one giggled and no one sighed. They were all good citizens in the country of desire, but in the dark there was no way to know if anyone managed a fleeting smile in homage to the irony of it all.