LOS ANGELES (AP) _ Billy Barty has been fighting discrimination for most of his 61 years, and for him it has been a winning battle.

Barty is 3 feet 9 inches tall, and his acting career, which started in 1928, is at its peak. But he remains devoted to his cause, and on non-working days he can be found at the North Hollywood office of the Billy Barty Foundation for Little People.

''We've got some big things coming up: a chili cookoff, a celebrity auction and our annual Billy Barty golf tournament in Palm Springs Sept. 12-14,'' he reported from behind his three-foot desk. The events benefit the foundation's work in helping little people adjust to their lives and work, promoting public awareness of their problems and helping in medical and legal problems.

''Our goal is an international headquarters and a retirement home,'' Barty said enthusiastically.

The ebullient Barty has never been busier. He has a major role in Paramount Pictures' current fantasy, ''Legend,'' starring Tom Cruise. He recently returned from Israel, where he appeared with Amy Irving in ''Rumplestiltkin,'' and he may return there for another fairy tale film. Before that he was on stage in ''Romance Language'' at Los Angeles' Mark Taper Forum.

''I just did a couple of other pictures,'' he said in an interview. ''In 'Body Slam,' which Hal Needham directed, I played a wrestling promoter and announcer, a cute little cameo. In 'Tough Guys,' I was one of the crooks that Kirk Douglas and Burt Lancaster tried to recruit to pull off a job. What a pleasure to work with a couple of pros like Kirk and Burt. None of the stuff you get from new actors today: 'What should I do?' 'How do I read this?' Those two guys know what they're doing.''

Billy Barty has been a pro since the age of 3. Born in Millsboro, Pa., to full-grown parents, he toured in vaudeville with his two sisters, also full- grown, made his film debut in a two-reel comedy, ''Wedded Blisters.'' He was busy in films during the 1930s, appearing in such musicals as ''Golddiggers of 1933'' and ''Footlight Parade,'' as well as ''Alice in Wonderland'' and ''Midsummer Night's Dream.'' His most memorable scene came in ''Nothing Sacred,'' when he ran out and bit Fredric March on the leg.

''I also made 75 'Mickey McGuire' comedies,'' he said. ''The star changed his name from Joe Yule Jr. to Mickey McGuire to Mickey Rooney. Mickey and Donald O'Connor and I have always kept in touch. We've known each other more than 50 years.''

Billy tried to break out of show business in the 1940s when he studied to become a sports announcer and journalist at Los Angeles City College. However, he was drawn into television, appearing on local shows and working as the host of his own children's program. From 1952-60 he toured as one of Spike Jones' zanies, then he returned to movies.

''My big breakthrough came with 'Day of the Locust,''' Barty said. ''That changed the perspective producers had of me. I was thought of as an actor, not just a little person being cute with Spike Jones. 'W.C. Fields and Me' followed. I was the last one cast in the picture, and Universal wanted to see footage from 'Day of the Locust.' The producer, Jerry Hellman, had his editor put together all my best scenes. I was really grateful for that.''

Barty is married to a small person, Shirley, and they have a daughter their size, Laurie, 23, as well as a normal-size son, Braden, 15.

His own talent has opened doors for Billy Barty, however, the discrimination against little people is still there.

''People do not understand the medical, psychological, vocational and social problems that can derive from being small,'' said Barty. ''Because of that, little people are not considered a part of society but as something strange and even laughable.

''I tell others my size that we can prove ourselves in almost every profession. There is a solution to every problem. ...

''We can drive by using special extensions. We can do the same thing that a six-foot person does to reach 10 feet - only we get bigger ladders.''