Does Someone Like This <i> Still</i> Have to Prove Herself? : Mary Steenburgen thinks she does. So, after two high-profile movies, she’s doing something that really terrifies her: hitting the stage.

Mary Steenburgen played very much against type in her last two films. In “Philadelphia” she was surprisingly convincing as a frosty, tough-as-nails lawyer, while “What’s Eating Gilbert Grape?” featured Steenburgen as a lascivious housewife in a permanent frenzy over a small-town grocery clerk played by Johnny Depp.

“Yeah, those love scenes with Johnny Depp--it was a tough job,” she says with a laugh, “but somebody had to do it.”

In “Marvin’s Room,” the Scott McPherson play that opens Friday at the Tiffany Theatre, Steenburgen returns to the sort of character she seems meant to play--a modest person whose innate goodness transforms her into a kind of goddess. Cast as Bessie, Steenburgen describes her character, an unmarried woman who has devoted her life to caring for her ailing father and aunt, as “a caretaker who performs her duties with great energy and love. One of my favorite passages in the play is when Bessie talks about how lucky she is to love two people so deeply. Most of us think of love in terms of how lucky we are to be loved, and I find her point of view quite wonderful.”

Meeting with the 41-year-old actress at a sprawling ranch-style house in Santa Monica Canyon where play rehearsals are being held, Steenburgen answers the door in bathrobe and slippers, then takes great pains to make the visitor feel at home. An unpretentious woman whose graceful manners are a credit to her Southern upbringing, Steenburgen was born in Arkansas--in fact, she spent her 40th birthday at the White House with two old pals from her home state, Bill Clinton and Hillary Rodham Clinton. The beautiful house she’s temporarily residing in has stellar credentials as well--it’s on loan from Ted Danson, with whom she has been linked romantically for the last year and who co-stars with her in “Pontiac Moon,” a romantic comedy directed by Peter Medak slated for release next month.

Steenburgen and her two children by her former husband, actor Malcolm McDowell, live two hours north of Los Angeles, so her weekly commute for the play, directed by Dennis Erdman, is a long one. She has no doubt, however, that it’s worth the drive.

“My friend Tom Hulce (who co-starred with Steenburgen in the 1989 film “Parenthood”) called and said, ‘Someone’s gonna offer you a play called “Marvin’s Room” and I urge you to do it,’ ” she recalls. “The last time Tom told me about something was when he mentioned a book he was reading called ‘What’s Eating Gilbert Grape?,’ so I pay attention to Tom’s tips. I read it and knew I had to do it--it’s an absolutely brilliant play that’s very funny in a dark, ‘Gilbert Grape-ish’ way.”

“Scott McPherson (who wrote “Marvin’s Room”) died of AIDS (in 1992, two years after the play was first produced), and though AIDS is never mentioned, what happens when you care for someone who’s dying is central to the play,” she continues. “The crux of the story is a visit from Bessie’s sister (played by Jean Smart) and her children--these people haven’t seen each other for 18 years, and for a brief moment they all become a family again. It’s a beautiful play in that beneath the broad comedy that keeps the story moving is another level about humanity, pain and irony.

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“This play is an amazing experience for me in so many ways. I’ve been meeting with people who are quite ill, which is really inspiring, and I’m facing one of my great fears--doing theater. I started my career in film and that’s a comfortable medium for me--I feel very relaxed in front of a movie camera,” adds the actress, whose career was launched in 1978 when Jack Nicholson spotted her in the reception room of Paramount’s New York offices and cast her in his directorial debut, “Goin’ South.”

“Onstage, however, I’m terrified,” confesses Steenburgen, who won an Oscar in 1980 for her performance in her second film, “Melvin and Howard.” “Last year I was in a production of George Bernard Shaw’s ‘Candida’ in New York, and eventually I got past my fear to the point that I looked forward to going to work, but that took a while. I always learn something when I face my fear though, so I make a point of trying to do that. I joined a swim team in 1988, for instance, and did some competitive swimming (she won a medal the first time she competed, so she was hooked), and I sang in a film I did in 1991 (“The Butcher’s Wife”).”

S teenburgen still sings for friends occasionally, and this isn’t surprising when one hears her tell of her initial infatuation with show business. Born in Little Rock in 1953, Steenburgen recalls, “my dad had a heart condition, and I grew up feeling Daddy could die any minute. As a child a doctor once told me my father needed a quiet place, which I interpreted as be perfect or your daddy will die, so I didn’t feel free to be anything other than perfect--which God knows I’m not, so the strain was enormous. What got me through was books. I read constantly, and I’ve always thought that immersing myself in the imaginary world of books was a creative way of dealing with a pressure that was too much for a child.

“I wasn’t a movie nut when I was growing up and wasn’t privy to classic films,” she continues. “I’d like to say I watched things like ‘Les Enfants du Paradis,’ but I didn’t--my favorite actresses were Hayley Mills and Ann-Margret.

“Actually, the pivotal events in my childhood were seeing ‘The Music Man’ on stage when I was 8 and a production of ‘South Pacific’ in Memphis a few years later. Those plays changed my life--I couldn’t stop thinking about them, and when I met one of the actors in ‘South Pacific’ and he said, ‘Look at that little girl’s eyes--there’s an actress in there,’ I loved it so much I could barely breathe. I’ve always thought my biggest break in life wasn’t meeting Jack Nicholson or winning an Oscar--it was that I always knew what I wanted to do.”

One of the things Steenburgen knows she likes to do is play offbeat characters. “In ‘Pontiac Moon,’ I play an agoraphobic who hasn’t left her house in seven years. What can I say?” she says with a laugh, “I’m attracted to that kind of thing.”

On the face of it, one might assume Steenburgen was making a concerted effort to get away from the “good girl” roles she’s come to be associated with, but she says: “No, I don’t think I’ve been typecast. If I have a problem of that nature, it would be that most people don’t know who I am, to the point that I have to keep proving myself.

“Prior to meeting with Peter Medak about ‘Pontiac Moon,’ I had a photographer shoot me in a wig and makeup that showed the character as I envisioned her,” she adds by way of explanation. “On the way to meet with Peter I talked myself out of showing him the pictures, though--it just seemed too desperate, although the reason I’d had them shot was simply because I loved the idea of the character so much. So, Peter and I met and talked a while, and finally he said, ‘I don’t know, darling. You know I love you, but I just don’t see you in the part’--at which point I pulled out the pictures. He looked at them a minute, then said, ‘You bitch--now I can’t imagine anybody else.’ “*

* “Marvin’s Room,” Tiffany Theatre, 8532 Sunset Blvd. Thursday-Saturday, 8 p.m.; Sunday, 3 and 7:30 p.m. Ends Nov. 13. $32-$34.50. (310) 289-2999).