The silent movie in the Prince George's County courtroom was in color, seven minutes long, and without a plot.

As a man and a woman grappled on screen in progressive stages of undress, a woman standing at a podium several feet away lectured the judge and jury on the action, like any good sportscaster.

"Now they're trying to simulate passion," said the woman in the beige cashmere dress, Loretta Haroian. "They're moving to a lot of regular positions, what everyone does in their bedroom."

As she lectured, the judge and jury of seven men and five women watched the movie with grave expressions, for what the witness was telling them would have an important bearing on the outcome of the case they were considering.

Haroian, who lectured the jury last week, is a sexologist from San Francisco who testified for the defendant, an employe of the Silver News bookstore in Hyattsville. The case was one of the three obscenity cases that went to Prince George's Circuit Court juries in the last two weeks.

During the next eight months, more than 40 obscenity cases will go to trial in Circuit Court and dozens of sexologists and psychologists will testify for the adult bookstores. The cases resulted from the arrests of dozens of adult-bookstore employes who were charged with distribution of obscene matter after selling magazines, books and films to undercover police officers between March and May. Police say the arrests resulted from complaints by county residents who live near the stores.

The task of the juries is to decide whether the material is indeed obscene; the task of psychologists and sexologists is to convince the juries that there is nothing terribly unusual -- let alone obscene -- about the magazines, books and movies that they are asked to judge.

So far, the sexologists apparently have been convincing. The adult-bookstore employe who sold the film that was the topic of Haroian's lecture was acquitted. And of the three obscenity cases that went to juries during the past two weeks, only one resulted in a conviction.

Defense lawyers say they began asking sexologists and psychologists to testify in obscenity trials in the late 1960s. But they have been calling upon them more and more during the past few years because of an increase in books and movies for homosexuals. In the case of movies for homosexuals, defense lawyers say, sexologists can explain to the jury that the intended audience would not see anything perverted or obscene about their content.

The adult-bookstore owners pay handsomely for the sexologists' time. During the three-day trial featuring the movie shown last week, for example, the owner of the Silver News bookstore paid several thousand dollars for the airplane fare, hotel bills and $50-an-hour fees of five sexologists and psychologists, according to court testimony.

A main tactic of the sexologists is to analyze the film or book, commenting on the work like any critic and thus encouraging jurors to see it as ordinary -- or at least to view it with less emotion.

In most cases, the sexologists also use the argument that they use films and magazines similar to those on trial to educate patients with sexual problems -- thus implying that the material has serious scientific value and is not obscene.

"The things that adults need to be educated about relate to sexual techniques and those techniques are best related on film," says psychologist Gregory Lehne, a research assistant in the psycho-hormonal unit of the Johns Hopkins University department of psychiatry. Lehne testified for the movie shown to the jury last week as well as for the two adult magazines that figured recently in a trial.

Such testimony, according to juror Thurman Battle, was one of several factors that encouraged jurors to vote for acquittal despite personal feelings on the part of a few that the movie was obscene.

At least two sexologists who testified about the scientific and educational value of the adult films produce their own adult films -- much to the consternation of prosecutor Gene Whissel. The sexologists, Haroian and Robert (Ted) McIlvenna, advertise their adult home movies in men's magazines. The movies are known as the "Sexual Pleasure Education Series." Their individual titles are "Sex Aids," "Gay Men," and "Approaches."

Prosecutor Whissel views the sexologists' movies as evidence of a conflict of interest in light of their trial testimony. "They have a financial interest in protecting pornographic material in the marketplace and they do it in the disguise of an educational interest," Whissel said. "I find it difficult to believe that people seeking educational material would buy it through advertisements in men's magazines."

Whissel also is troubled by the credentials of Haroian and McIlvenna. Both have doctorates from the Institute for Advanced Study of Human Sexuality, a school that McIlvenna started in 1976. The school is not accredited by the U.S. Department of Education, which approves most legitimate universities, although the California Department of Education has licensed the school to operate.

Tuition at the school is $4,200 a year; the school's 100 students earn their doctorates after writing a dissertation and taking such courses as social and sexual relationship skills; homosexual male, lesbian and bisexual life styles; the body; children and sexuality, and the homosexual movements in the United States.

Psychologists at Yale and Johns Hopkins universities say they do not view sexology as a legitimate academic discipline, although some psychologists -- like some of the psychologists who testified at the trial -- choose to specialize in fields similar to sexology, like marriage and the family and intimacy in sex. Unlike the sexologists who get their degrees from the institute in San Francisco, psychologists who specialize in sex do so only after they have a thorough, rigorous background in the field of psychology, according to Ervin Childs, chairman of the psychology department at Yale.

But Lehne, a psychologist who testified at the trial, is more liberal in his view of the men and women who graduate with doctorates in sexology from the institute in San Francisco. "Sexology isn't an established subdiscipline like child psychology," Lehne says, "but it is a specialty in the field of psychology."