On the tenth anniversary of film industry's rating system, Jack Valenti, president of the Motion Picture Association of America, has contemplated his handwork and pronounced it a "steady and sturdy" institution. According to Valenti. "The curve is up on public endorsement of the rating system: it is part and parcel of the American scene today."

Each year the MPAA, the trade organization representing the major film companies, publishes the results of a poll to determine attitudes toward the ratings. A sample group of 2,184 people age 18 and over is asked "How useful do you think the motion-picture industry's rating system - with the symbols G, PG and X - is as a guide for deciding what movies children should see - very useful, fairly useful, not very useful or have you not heard of the rating system?"

The 1978 survey indicates that two-thirds of the moviegoing public regards the ratings as fairly to very useful. About 27 percent of the sample do not. Among nonmoviegoers, 33 percent regard the system as useful, 27 percent do not and 40 percent have no opinion - which only seems fair. Among adults with children the system is judged useful by 60 percent and not useful by 29 percent.

Five years ago, when the approval rate went over 50 percent for the first time, an MPAA press release described the results as a "landslide," so Valenti's satisfaction with the latest survey seems fairly justified.

It is interesting that the most substantial increases in the approval rate seem to have coincided with a resurgence of attendance. For example, the useful rose from 55 to 64 percent between 1972 and 1974, while the not-usefuls declined from 36 to an apparently sturdy bottom of 27 percent. Attendance began to climb after the success of "The Godfather" early in 1972, ending a two-year slump that cost the majors an estimated $500 million. Between 1976 and 1978 the surveys indicate a gain in usefuls from 59 to 65 percent and a drop in not-usefuls from 31 to 27 percent. A string of hits like "Jaws," "Rocky," "Star Wars" and "Saturday Night Fever" probably influenced these fluctuations.

When Valenti arrived at the MPAA in May of 1966, he quickly preceived a system of self-regulation as the industry's most urgent need. Since then, he's been able to improvise and protect a mechanism that will probably last as long as it needs to.

"The rating system has held up," Valenti observed in the course of a recent interview. "Any politician would believe me. The biggest thing that rating system has done is keep the government out of our business. In 1968 the Supreme Court handed down two decisions that made it perfectly legal for states or localities to organize their own rating systems. None has caught on since we began a rating system, and the threat lessens every year. . .

"The thing that makes our system good is that it's flexible. It bends with the times. It hadn't, it would have cracked by now. It's a canopy under which a filmmaker can make his story."

Looking back over the history of his creation, Valenti realizes that "I entered the movie business at a watershed period. None of us recognized it at the time, of course, but it was clear that something had to give. You had the war in Vietnam, a loosening of sexual restraints. Movies were bound to be medium most affected by changing mores. I had only been on the job three weeks when "Virginia Woolf" came up. Now it's like a training film for nuns, but then it was a shocking intrusion.

"As I listened to Jack Warner and his associates debate whether they should cut a 'screw' and leave in a 'hump the hostess' or vice versa, it dawned on me that whatever procedures we had under the old Production Code weren't adequate to deal with these changes. Soon after you had the teenyboppers running around in 'Blow-Up.' When it didn't get Code approval. MGM released the picture through a subsidiary, and it became a prestige hit. For a time we experimented with a 'Suggested for Mature Audiences' tag, but that didn't work.

"When the Supreme Court found it constitutional to protect children from material that might be denied to adults - the so-called variable obscenity doctrine - it didn't take long to figure out that the movies would be inundated by classification systems. So we started discussing a self-regulatory system among ourselves in May 1968, brought in the exhibitors and independent distributors and importers and had it put together by the fall."

Valenti would have preferred an age limit of 16 rather than 17 on the restricted K rating, which required under-age customers to be accompanied by a parent or adult guardian. he felt 17 was realistically high for the fast changing late '60s but deferred to exhibitors, some of whom felt constrained to impose an age limit of 18 on the R if local customs and laws demanded it. Valenti also deferred to exhibitors on the X rating. He had proposed a three-category system, but exhibitor representatives urged a fourth barring attendance by children, mainly as a defense against possible prosecution under local or state laws.

Among some exhibitors, that X designation also was presumed to have special commercial appeal for customers in the market for hot stuff. "If I had it to do all over again," Valenti said, "I wouldn't have called the category X, but I'm convinced that if we had called it A, C or Sweet Jesus, it would still have become a no-man's land. The hard-core porn was bound to end up there and blight everything else.

"At the start we intended for the X to include fine, serious pictures. It would be our way of protecting movies that tried to experiment that way Joyce had in 'Ulysses.' Well, that was delusion. As a result of the benighted influence of the porn, it tarnished everything in that category. Ultimately, common sense demanded that the serious pictures originally rated X - 'Midnight Cowboy,' 'Medium Cool,' 'Clockwork Orange' - be reevaluated. Under our procedures, a producer can withdraw his film from release for 90 days and then re-submit it for rating, with or without re-editing. As I recall minor cuts were made on 'Midnight Cowboy' and 'Clockwork Orange' before they were re-rated R."

The rating system is voluntary. For enforcement the MPAA depends on the cooperation of exhibitors. It cannot apply sanctions. Theater owners themselves estimate that the ratings are enforced systematically at 80-85 percent of the theaters in the country.

This percentage may have taken a plunge in the case of an R-rated sensation like "Saturday Night Fever." Several exhibitors have confided that box-office vigilance tended to slacken during weekdays because of the film's intense, ongoing appeal to young customers. With lines around the block on weekends, it was easier to be choosy about I.D.s.

More often than not MPAA literature will maintain that "the only objective of the ratings is to advise the parent in advance so he may determine the possible suitability or unsuitability of viewing by his children." In fact, this public relations objective emerges out of a self-interested objective to protect the film business from local, state or national censorship.

Typically, it has taken crisis situations to provoke acknowledgement of the dual purpose. For example, responding to serious criticism from Catholic and Protestant church agencies in June of 1971, Valenti spoke of the "two chief objectives of the rating program: First, to serve the public interest by informing parents about the content of films for children: and second, to stave off government intervention." The order might have been reversed, but the candor was refreshing.

Attacks on the rating system seemed to proliferate and peak during the chairmanship of Dr. Aaron Stern, a professional psychoanalyst who served as a consultant to the ratings board for two years before being appointed to head it in June of 1971. Before Dr. Stern resigned three years later, some younger critics had created the impression of an almost satanic censorious personality, imposing compromise on helpless filmmakers.

Curiously, the filmmakers alleged to have been interfered with tended to defend Dr. Stern. For example, Don Siegel, Sam Peckinpah and Ernest Lehman maintained that dark rumors to the contrary, Dr. Stern had not blunted the impact of "Dirty Harry," "Straw Dogs" and "Portnoy's Complaint," respectively either in the script or editing stages.

In an extensive interview published in the Los Angeles Times in July of 1972, Dr. Stern emerged as a subtly intelligent temporizer rather than the second coming of Dr. Mabuse. "My own prejudice," he said, "is in the direction of letting as many people see as many films as possible, so they can judge for themselves. To maintain my commitment to that freedom, I have to live up to some of the policies communicated by society. . . I may try to stimulate, but I must always accept the rate and direction of society. When you try to move people at your rate, you very often firm up resistance."

Stern's moderation and caginess undoubtedly harmonized with Valenti's outlook. In retrospect, the eagerness of some of their detractors to ditch the rating system, challenge every potential censoring agency legally and Let the Courts Decide, seems more bizzare. In many cases it reflected wrong guesses about the rate of social change, presumed to be accelerating at an unstopplable liberal clip, and the movie market, which was presumed to be fragmenting into specialized little audiences that would never see the return of old-fashioned mass audience pictures.

Filmmakers can feel grateful that the MPAA leadership felt more inclined to disarm censorious elements that smite them hip and thigh in some litigious Armageddon. "You cannot ignore the realities of the change in the Supreme Court." Stern remarked. "You cannot ignored the reality of an adminstration deeply committed to states' rights and local autonomy or the fact that, as the moment, the states have the power to define obscenity for themselves.

"The toughest part of the job is to be skilful enough to live up to the social mandate so that you don't destroy the system, and at the same time try to institute a positive thrust toward change."

As the second decade of the rating system begins, Jack Valenti, chief diplomat of the American movieegins, Jack Valenti, chief diplomat of the American movie business, seems to have achieved that equilibrium.