A public backlash may have begun against violence in films which is causing producers to tone down violent scenes before movies are released, according to film industry observers here.

Main victim so far of the backlash is "Rolling Thunder," a $1.8 million production which has failed to find a distributor since an audience reacted angrily to it at a recent preview.

Shouting, booing and screaming erupted in the audience at San Jose, Calif. when the hero's hand was mashed in a sink waste disposal unit in a torture scene, according to witnesses at the screening.

The film was originally to have been distributed by 20th-Century Fox studios but a Fox spokesman said yesterday it is no longer on their distribution schedule.

Another recent film substantially toned down before its release was the thriller "Marathon Man."

Paramount studio sources say 117 cuts were made in the film after a large part of the audience walked out at a San Francisco public preview.

Los Angeles film critic and historian Charles Champlin says he believes public reaction to the violence in the film hurt it at the box office.

"A domestic gross of about $30 million was predicted for the film, but it is only going to wind up at about half of that -- which is still pretty good," Champlin said.

Arthur Knight, another local film historian, says' "I believe there is an increasing awareness among film producers about violence and the need to trim it in some way."

He says he does not see any industry-wide desire to cut back on violence in movies.

"But where a film has been made already and the public reacts badly trimming is being done. I think that is the way it is going to happen."

"Rolling Thunder" producer Norman Herman says he thinks the film had a bad first preview because it was shown to the wrong audience.

"Some girls started screaming and their boyfriends got angry," he said.

He said the film was shown to another preview audience recently and got a good reception.

"You just have to pick your audience," he said.

The film, which stars William Devane as a returning Vietnam war prisoner who gets into trouble with gangsters, was written by Paul Schrader the author of another violent epic "Taxi Driver."

"It had one rocky scene in it," Herman said. "We toned it down but we toned it down too much. We are going to have to restore part of it because with the cuts it didn't make sense."

He said part of the reason for the unfavorable first reaction may have been that the man tortured was a former prisoner of war. "We all feel bad seeing things happening to people like that."

Herman said negotiations were under way to make other distribution arrangements for the film.