Irish-American beauty Joycelyn O'Brien makes her movie debut in "Oscar" this month with Sylvester Stallone, Kirk Douglas, Don Ameche and Yvonne De Carlo, most of whom were established stars before she was born.

But, filled with confidence, O'Brien tackled her assignment as the housemaid of a Mafia don, played by Stallone, with enthusiasm.After all, she gets to yell at him.

"I get to give him lots of lip in the script," O'Brien said happily in an interview. "The first day I met him I told Sylvester the best part of playing the role was that I got to scream at him."

A startled Stallone wanted to know why.

"I said, `No one ever gets to talk back to you.'

"He said, `What do you mean? Guys are always yelling at me.'

"I told him, `Men, yes, but women never get to scream in your face.' And then he laughed. Sly is a very nice guy and was a big help to me.

"It was incredible working with so many great actors. I was impressed, but I wasn't too nervous when I auditioned. Nor did I get uptight when I reported to the set because the atmosphere was so cordial. I lost my fear.

"I might have been frightened if my first scene had been with Don Ameche. Fortunately, it was with Sylvester and he was very outgoing and friendly.

"It's a different thing with Ameche and Douglas. They are institutions and very quiet. They pretty much kept to themselves. But Sylvester was always available and less intimidating after I got to know him.

"When Sylvester first walked on the set I was taken aback by his presence. He carries himself like a prizefighter, a champion, aloof and reserved. He walks like a king. He presents himself as Hollywood royalty.

"Plus the fact he's gorgeous and looked like a million dollars. There were several people around him, including his producers and a bodyguard. It was a little intimidating.

"But when we did our first scene he loosened up and his true nature surfaced. He goofed around with all of us and became very sweet and very funny. I had never seen that part of him on the screen. He's a very special man."

While her role as the sassy Irish housekeeper is a minor one, it is of vital importance to her ambitions to establish herself in movies.

A native of Chicago, she studied drama at Northwestern University and spent a year at London's Royal Academy of the Dramatic Arts, where she appeared on stage in "Kennedy's Children." Back home in Chicago she appeared in 18 plays, gaining experience.

O'Brien made her Broadway theatrical debut in "Biloxi Blues" and starred in road companies of the Neil Simon play and in his "Brighton Beach Memoirs." She has appeared in several TV movies, but like most young actresses, feature films are a major lure.

"I wanted this part in `Oscar' badly," she said. "I knew it was a role I could do well.

"I had met Jackie Burch, the casting director, for another picture. She tried to cast me in `48 Hours Part II' and `Die Hard 2.' But they cut the woman's role out of the `48 Hours,' and the director had someone else in mind for `Die Hard 2.'

"When `Oscar' came along, Jackie wanted me for the part of the housekeeper. She found a woman who had just arrived in Hollywood from Kilkenny, Ireland, to coach me in an authentic Irish dialect. And she kept pushing me with John (Landis, the director).

"I met with John and he liked my interpretation. He gave me the part in his office after the audition. He told me, `I want you in my movie.' I was dumbstruck."

It took O'Brien two years in Hollywood to progress from theater to television to movies.

"I'd been doing TV auditions for almost two years," she said. "My experience was mostly in small, supporting roles in TV films. You can understand that my first feature movie is very important to me and my future.

"When I was younger my goals were different. I wanted a career in theater. I'll always want to work on stage, but some of the best, most interesting things in entertainment today are being done in movies.

"Now I hope the picture is well-received. Disney is going to release it March 15, so I'll find out soon enough."