THE PARTICIPANTS wore little plastic nameplates, they carried briefcases and note pads, they huddled at the coffee urns during break periods and they flipped anxiously through their programs as they scurried this way and that in quest of the sessions of their choice. They even stood at attention for the playing of the national anthem when they gathered here Monday morning.

But if you stopped by the Washington Hilton this week for the 6th World Congress of Sexology and thought if looked pretty much like any other big professional convention, all you had to do was look at some of the issues being addressed, or listen to some of the words being spoken, and you were set straight.

"The Two-Nerve Theory of Orgasm," "The Forensic Sexologist in an Adversarial Trial System," "New Directions at the Kinsey Institute," "Sex Tonics in Ayurveda" and "Prostitution and Population Dynamics in Peking 1912-1950" were just a few of the matters an eager student could learn about.

In a paper entitled "Sex Therapy in a Country in Crisis--Argentina: The War of the South Atlantic," Laura S. Caldiz of Buenos Aires spoke about the conflict between "psychic space for war and psychic space for pleasure."

In a paper entitled "A Study of the Married Bisexual Male: Paradox and Resolution," John J. Brownfain of the University of Michigan said his eight-year research project had revealed that while the public tends to think of such men as "torn" or "desperate," "it's not necessarily so."

More than a thousand delegates registered to attend, making the congress, which ended yesterday, "the largest sexological meeting ever held in the world," according to William A. Granzig, president of the sponsoring organization, the United States Consortium for Sexology.

People came not only to talk and to listen, but to make contacts, to build reputations and to buy and sell.

Michael Carerra, who writes a sex advice column for Glamour magazine, counseled fledgling sex columnists to "try not to always end by saying, 'And if this doesn't work, go see somebody.' "

Paul Probst, vice president of the Minnesota-based Dacomed Co., set up shop in the exhibition hall and corralled passers-by with a pitch for his new Snap-Gauge Impotency Testing Device, which is capable, he explained, of determining a man's need for another Dacomed product, a penile implant.

It was a diverse group by some measures, a distinctive one by others. The participants were, to say the least, "more liberal than the average person," as veteran sex researcher Wardell Pomeroy politely put it. But they were not above having a few vigorous disagreements.

The advocates of sex-change surgery were on hand to defend the validity of their procedure. Patients have emerged feeling far happier than conventional wisdom would suggest, according to Sharon B. Satterfield, who has been studying this matter at the University of Minnesota. Although follow-up is difficult because sex-changees tend to be hard to locate and reluctant to talk, "we found that in general, these patients were quite happy with their lives," she said.

But Leslie Lothstein, an Ohio therapist, spoke of the virtues of dynamic-expressive psychotherapy as an alternative to surgery.

Lothstein and others testified about the extraordinary desperation of some transsexuals. Before the rigorous pre-surgery interviews, "Patients have actually gone out and rented surrogate parents to corroborate their stories--including other transsexuals who impersonate their mothers," said Paul Walker, a San Francisco therapist.

Meanwhile, white-haired sex educator Mary Calderone used her welcoming remarks as a vehicle to urge more emphasis on education and prevention than on medical wizardry. "I can't think that anyone would be happier than Masters and Johnson and Helen Singer Kaplan," she said, "if their livelihoods were phased out--slowly, I would hope, so that they could get used to it." The sex surveyor Shere Hite was there, too--but belatedly so, and noticeably angry upon finding a three-quarters-empty room for her presentation. "I've never heard of him!" she complained when officials told her that the chairman of her panel, Mark Schwartz of the Masters and Johnson Institute, had terminated the proceedings because of her failure to arrive on schedule.

When the TV cameras were properly set up, however, Hite and Toshiyasu Ishiwatari of Japan's Nihun University went ahead with their comparative analyses of male sexuality in Japan and the United States.

Ishiwatari reported that young Japanese males are less committed to the conventional model of masculinity these days. They are interested in "showing more tenderness and expressing one's emotions," he said.

By contrast, Hite reported that James Bond remains the preeminent role model for American males. "The basic bottom line for most men is to be in control--whether in control of feelings . . . or your car," she said.

Why do people become sexologists?

"For the same reasons they choose any other profession," Pomeroy answered gruffly during a lunchtime recess.

Sexology, Pomeroy explained, is an umbrella term covering physicians, teachers, sociologists, philosophers and others who have decided to study the subject of sex.

"It's grown tremendously" since the years of his own early work with the Kinsey Institute for Sex, Gender and Reproduction, he said. "It's more solidified in the sense that we're now thinking of sexology as a science." But the field still hasn't been accepted by everyone, he added, which may be one of the reasons few sexologists actually call themselves that. And to this day, said Pomeroy, "Research grants are very difficult to come by."

Nevertheless, Pomeroy braved some bold long-term predictions about American sexual behavior, including "a very gradual and small move toward androgeny"; acceptance of homosexuality and bisexuality "as people become aware that these people are not devils but your friends and our friends"; the proliferation of sex on cable TV ("and people will become bored and sated so that only the best will remain"); an effective male contraceptive; a cure for AIDS (only after an increase in cases involving heterosexuals and a resulting infusion of new research money), and the recognition of sexology as "a science in its own right."

But a more somber note was sounded by Irwin Haberle, Pomeroy's colleague at the Institute for Advanced Study of Human Sexuality in San Francisco. Haberle traced the origins of sexology in prewar Europe--a heritage most of today's sex experts know nothing about, he said, because when the Nazis came to power, "the sexological pioneers, most of them German and Austrian Jews, had to flee . . . and a whole promising young science fell victim to the Holocaust."

The mood of the congress was basically do-your-own-thing, but some delegates were scandalized by a Monday night "Media Extravaganza" featuring pornographic movies and the live presence of a few of the actors and actresses.

"I have never in my professional life been eye to eye with people like that," said Judith Jones, a sex educator from Australia. "We are all liberals and more comfortable with ourselves than other people, but some of us feel that the adult film scene is almost totally destructive."

The sessions on homosexuality reflected a shift away from the preoccupation with possible causes or "cures" toward questions of interest to committed gays. Many of today's researchers in the field are homosexuals themselves, said Frederick Suppe, a philosopher of science at the University of Maryland who is doing a critical history of homosexuality research.

He said much of the medical and psychiatric professions' work in this area has been "scientifically inept," because of highly abnormal populations, lack of control groups and the use of "eyeball measures" rather than objective criteria.

"We're at the end of an era about how to think about these questions," said sociologist John Gagnon, who challenged claims of a correlation between "gender nonconformity" in childhood and homosexuality in adulthood. The studies that have identified such a link have been based on interviews with adult homosexuals, Gagnon said, and "the human memory is a dreadful sieve. There are no grounds to believe it will retrospect to childhood with any degree of accuracy."

He also condemned conventional theories for their focus on negative experiences as possible explanations. "I don't know any theory of homosexuality development which talks about good things," he said. For example, he asked, why do the studies never report responses such as, "I got to be gay because I fell in love with someone who was wonderful?"

An unusually vigorous ovation followed the presentation by the Austrian sex researcher Ernest Borneman, who is conducting a massive study of childhood sexuality involving more than 4,000 subjects.

Borneman said his investigations have led him to question Sigmund Freud's idea of a standard sequence of oral, anal and genital phases in human psychological development. And the Oedipal complex is not a universal fact of life, he said, but "the product of the nuclear family."

Borneman also said he was finding more and more boys playing girls' roles. He had detected signs of "bosom envy" among Austrian youths, he said, along with pronounced envy of the female ability to bear children.

"While our body matures earlier and earlier from generation to generation," said Borneman, "our minds mature later. Almost all sexual problems stem from this fact."

At the other end of the age spectrum, Dr. William H. Masters gave a talk on "Sex and Geriatrics" in which he recalled his proposal to establish what he called "recreation rooms" in nursing homes. ("That seemed like a good name for it," he explained.) One nursing home official liked the idea, but told Masters: "In all truth, we're concerned that the younger people who are supporting their parents will take them out of the home."

"And that's exactly what happened," Masters added.

Masters and his wife and colleague Virginia E. Johnson attracted the most attention at the congress. They drew many stares and many clicks of cameras, and a standing ovation when they defended themselves against accusations of loose management and overstated claims for the work of their sex therapy institute in St. Louis.

Several other speakers went out of their way to praise Masters and Johnson. "We all owe them a debt of gratitude," said therapist Shirley Zussman. "Just as the successful flight of Sputnik spurred scientific and technological promise, so the publication of Masters' and Johnson's pioneering report . . . spurred many to enter this new field."

Another leading sex therapist, Helen Singer Kaplan, paid a lengthy tribute to Masters, Johnson and other early figures in the field. "As little as 10 or 15 years ago, a patient with a sexual problem was in very deep trouble," she said. "A person with what we now know to be a simple problem was pretty well doomed to a lifetime of sexual inadequacy.

"Today," she said, "a patient with a sexual problem is fortunate indeed."