Two unions representing about 90,000 Hollywood actors are concerned about a new twist in their members' perennial quest to break into films and TV shows.

Opening negotiations last Thursday for a new three-year industry-wide performing contract, the Screen Actors Guild and the American Federation of Television and Radio Artists said producers, directors and casting directors may be offering union actors -- only about 20 percent of whom make a living in their trade -- the faint hope of screen roles in exchange for paid acting classes.

Some union officials expressed concern that acting workshops operated by casting directors may be replacing the small clubs and theaters where actors traditionally have waited to be seen by directors and casting directors.

In the words of one experienced actress, who asked not to be identified by name, attending the paid classes is tantamount to "paying for a job interview." Casting directors, however, say that no such guarantee is made.

The controversy surrounding the issue became known last week as the two unions began negotiations with the Alliance of Motion Picture and Television Producers.

"We have had a rising tide of complaints," said Mark Locher, public affairs director for the actors guild. "In order to be seen, actors need to pay to participate in a showcase, a workshop or a class . . . All of these have been booming in the last three or four years. It's a new development."

The two unions are demanding an end to acting schools, talent showcases, workshops and seminars operated by producers, directors or casting directors who collect fees from aspiring performers.

However, one of show business' leading casting directors countered that the unions are stepping out of line by trying to tell casting offices "how to perform their trade."

Because the actors unions do not contract directly with casting directors, the unions are aiming their complaints at producers.

The actors guild has had two committees investigating the workshops for the past year and a half, Locher said, with the cooperation of the Casting Society of America, a 165-member professional organization of casting directors, founded in 1980.

"We have been meeting over the last year with casting directors trying to work this out," Locher said. "I wouldn't call this a huge adversary issue."

Casting director Mike Fenton of the Fenton & Feinberg agency on the lot of 20th Century Fox studios is one of the business' most prominent members and one of the founders of the casting society.

Fenton said most casting directors in talent workshops offer only to "open the eyes" of performers to the techniques of landing jobs in show business. The presence of the casting director is no offer of employment, Fenton said.

Rules of membership in the Casting Society of America, Fenton noted, specifically bar casting directors from accepting teaching positions with schools that offer employment as an inducement to enroll.

Society members, who are allowed to designate themselves by the initials CSA after their names, also are barred from participating in so-called "one-on-one showcases," in which the casting director merely sits in the audience watching actors work, rather than engaging them in a teacher-student dialogue.

"I don't know of a casting director who is getting rich doing these things," said Fenton, who teaches classes himself. "I don't need the little bit of funds they give me for going there once a week. If I thought I were not performing a good deed, then I wouldn't be doing it."

Many actors fear that speaking out about the practice could harm their careers, and most contacted asked not to be identified in the newspaper.

"The attraction basically is to get work and to get known," one actor said. "The one hope that a lot of actors and actresses go out for is to meet casting directors. I think it's a rip-off."