When she was 8, Annette Bening was already thinking about her plum role. Not onstage or on-screen. In life. She wanted to be a mother.

She just knew. The acting would come later. So would the marriage to Warren Beatty. For the time being, she fantasized about the children she'd have. By 13, she was the go-to babysitter in her San Diego neighborhood.

"I was baby-sitting like crazy," says Bening, who sits sideways on a hotel sofa, feet up beside her. Like she's home.

That baby-sitting was in the early 1970s. Picture the era. The Mark Spitz mustaches. The bellbottoms. And a husband, somewhere in San Diego, telling his wife: Wanna see that Warren Beatty picture? That Annette girl can take care of the kids.

Now, Bening's a bright, rangy, relaxed and beautiful 46. She's the mother of four: Kathlyn, Ben, Isabel and Ella. And yes, we know the rest. But she hasn't been doing the festival circuit in Toronto (where "Being Julia" opened the fest) and New York to extol the virtues of motherhood. She's on the road to talk about "Being Julia," which opens in Washington this weekend and which happens to be about role playing. Her character, a stage actress in 1930s London, is forced to find her truest self under the layers of roles she plays in life and onstage.

"You see me, an actress, playing the part of an actress who's also playing various parts in a number of ways," says Bening. "And you also see her sort of strip down. . . . This is a woman whose masks fall away. Once I heard an actress say, 'Good acting is about taking off a mask. Not putting one on.' It's all about that."

In the film, based on a W. Somerset Maugham novella, Julia Lambert (Bening) is a well-known performer on the London stage. She's contentedly married to an impresario (played by Jeremy Irons), but their physical relationship seems to be over. She's also at her career peak, but over the course of the film she will teeter and face a devastating descent. So when a chipper young American named Tom Fennel (Shaun Evans) showers her with a fan's adulation, sends her flowers and courts her heedlessly, Julia's not only charmed, she's seduced. An inviting new role presents itself: to be an illicit, vigorous, youthful lover. Julia seizes the opportunity. And relishes the role -- until she learns Tom's true agenda.

Julia is a woman, as they say, of a certain age, not unlike Bening. And yet the difference between the character and the real Annette Bening is stark. Julia is consumed with her appearance and her years. She watches people around her with a sort of hair-trigger calculation.

But Bening, who sat for two interviews in September in Toronto and recently in New York, is quite another spirit. She's completely at ease with herself, eager to go down intellectual paths of discourse, with talk of Thornton Wilder (she's a big fan), an acting mentor who once told her to find "a sense of wonder," and of Maugham's ability to create "underpinnings of ache under the characters." And there's also that ringing laugh with the head thrown back -- the gesture you've seen in so many films, from "Valmont" to "American Beauty."

Bening's beauty seems organic; there's a sort of corn-fed purity to her skin. Her face could adorn a new postage stamp series or even currency. (Is there a slot for a $3 bill? Or a $25?) And it's hardly surprising that artists used her features as inspiration for the latest Columbia Pictures logo (you've seen it, the gowned woman on a pedestal with torch aloft, framed by clouds). Age is subtly settling in -- after all, she can see 50 from where she's standing -- but that change doesn't look like deterioration as much as fascinating evolution.

It's inescapable: Annette Bening loves being Annette Bening.

After all, it's a life that allows her to be picky about her roles, she admits. She says she was attracted to "Being Julia" for its role-a-coaster ride; Julia experiences stagy histrionics, private heartache, romantic exuberance, deep gloom and, finally, vengeful artfulness. She plays them all with a mellifluous flourish, as if she's having fun shifting among the many Julias rather than putting on a laborious diva show. There's something very affecting about these changes; you can feel a tortured, real Julia desperately trying to find herself.

Bening loved the idea, she says, of a character who plays so many parts and yet always remains herself.

"We all perform our lives in a way," says Bening. "And the actor is a perfect metaphor to get at that theme of 'how do we find our authentic selves?' And that we all -- whether we're actors or not -- perform ourselves. As a way of searching. As a way of fumbling around and trying to say, is this my voice? Is this who I am? What kind of woman am I? Am I the woman that I am when I'm with my children? Or when I'm with my husband? Or with my girlfriends? Or when I run into my old boyfriend? You know. We're all searching."

Most actresses love to talk about their process, but coming from Bening, discussion of craft sounds more deeply considered than "Inside the Actors Studio" blabbery.

But actresses don't always love to talk about the process of snagging quality roles as they get older. "Being Julia," in which an older actress (at least by theatrical standards) must battle attitudes and preconceptions about her age, could be seen as a metaphor for women over 40 today. Has the pile of scripts dwindled lately for Bening?

Bening, who allows that her high-profile status and connections may yield more opportunities than most, says she hasn't experienced a drop-off. But "there is a cultural bias and a certain amount of sexism still around that women are subjected to. . . . But you don't have to agree to that or internalize that."

Those women, like herself, who are "in a position to get movies made, have got to find the material. You've got to read the books. You've got to rassle some great screenwriter into adapting it for you. Or adapt it yourself. Or direct it yourself. Or take somebody by the lapels to direct something you believe in."

No lapel-crumpling was required for "Being Julia," however; producer Robert Lantos and director Istvan Szabo approached her with the role. And Bening's career shows no sign of flagging. In the upcoming HBO drama "Mrs. Harris," she squares off with Ben Kingsley. He's Scarsdale Diet doctor Herman Tarnower, and she's Jean Harris, who was convicted of his murder in 1981.

Bening's also attached to the film "Under My Skin," with Broadway director Michael Mayer, a 1960s drama that casts her as an uninhibited divorcee. And Variety has reported she'll star in "Diva," playing an aging sitcom actress in a film that "explores the forces that contribute to the creation of a prima donna."

What has helped, throughout her career, Bening says, is to come from the background she did.

"There was always stability. It was so different from show business," she says.

Born in Topeka, Kan., she was the youngest child of Grant and Shirley Bening, Iowa natives and Republican Episcopalians. She was also the baby sister to Jane, Brad and Byron. Her father, a life insurance executive, relocated to San Diego when she was 7, and she attended Patrick Henry High, where the shy Annette became interested in acting. Little Annette Bening played in "Godspell," among other school productions.

"My parents were very supportive," Bening says. "They went to every show. And they never told me not to do what I was doing."

She studied drama at San Diego Mesa College and San Francisco State University. In 1980, she joined the well-regarded American Conservatory Theater in San Francisco and met actor J. Steven White. They married in 1984 and lived in Denver, where Bening began her career, appearing in such plays as Chekhov's "The Cherry Orchard."

White, it turned out, would not be father to those future children. The marriage crumbled after two years. Bening moved to New York and launched herself full time into acting. She was nominated for a Tony in 1987 for "Coastal Disturbances" on Broadway. And she turned her sights to the movies. Her first role: the snotty wife of Dan Aykroyd in a mediocre 1988 John Hughes comedy, "The Great Outdoors."

It got better. There were strong reviews for her performance as the sexual provocateur Madame de Merteuil in "Valmont," Milos Forman's 1989 version of "Dangerous Liaisons." But the real breakthrough came that same year for her effervescent performance as an unabashedly sexy schemer in the 1990 "The Grifters," which was nominated for four Oscars. Bening, who starred along with John Cusack and Anjelica Huston, was nominated for best supporting actress.

"That was when I became well known," says Bening. "And that was before I met my husband and all of that."

"All of that" took place the following year. As the feisty Virginia Hill in the 1991 "Bugsy," she found herself opposite Beatty's Bugsy Siegel. One of her first onscreen lines to him was: "Why don't you go jerk yourself a soda?"

Beatty, whose long list of previous lovers have included Leslie Caron, Natalie Wood, Julie Christie and Madonna, not only fell in love with Bening, he proposed. They married March 12, 1992, when their first child, Kathlyn, was 2 months old. Bening was 33. He was about to turn 55. There would be three more children over the next eight years. Bening, who had to pass up the Catwoman part in the 1992 "Batman Returns" because of her pregnancy, was finally a mother.

Between babies, she still managed to act throughout the 1990s, in "Love Affair" (co-starring Beatty), "Richard III," "The American President," "Mars Attacks!," "The Siege" and the underrated "In Dreams."

Her second breakthrough role came in 1999, as the chilly real estate agent Carolyn Burnham in "American Beauty." The character's initial archness segues into vulnerability, thanks to Bening's irrepressible sparkiness. There's a human being under that driving ambition who's painfully aware of her foibles. Watching, you can't imagine she's the ice queen that Kevin Spacey's character makes her out to be.

But she had to miss the movie's opening at the Toronto film festival, where "American Beauty" won the People's Choice Award, because she was pregnant with Ella, child number four. Six months later, a very pregnant Bening made it to the Oscar ceremony, where she was nominated for best actress (Hilary Swank won for "Boys Don't Cry"), and where Beatty accepted the Irving Thalberg Award.

After "American Beauty," Bening took off for three years for full-time mothering. And when she did return, for last year's "Open Range," she persuaded co-star and director Kevin Costner to shoot her parts within two weeks so she could minimize her time away from home. Beatty and family came to visit her on location in Canada throughout. As Sue Barlow, Bening is, in a sense, reprising the valiant frontier women of the old John Ford pictures. She's strong, full of take-charge confidence and guarding a femininity that she'll reveal only to the right man. Perhaps this persona is not too far removed from the mother and partner she clearly aims to be in real life.

Bening says the years she spent at home with her kids have been vital because "they experienced me as a mother for a long time. I was like every other mom."

Except she's still Annette Bening. And Mrs. Warren Beatty.

"You've got to make peace with it," says Bening. "By and large it's okay. You're an object of people's projections, certainly with my husband being so famous for so many years. That's out of your control. . . . Now I'm more used to that irony -- that, one minute, no one's paying attention to you, and the next, everyone's fussing about you running around and taking your picture." (Beatty is also in the spotlight this fall; he will receive a Kennedy Center Honor in December.)

What concerns her most, she says, is the effect on her children, who are now 12, 10, 7 and 4.

"You try to avoid a big schism between who they experience as their parent and the person that people perceive in public. If someone runs up to them and says something about a tabloid or a photograph or something they've heard, I explain it to them afterwards. I have to have some faith that they'll be able to handle this."

Although she's politely forthcoming about her private life, there's something in her tone that deftly closes an elegant door of privacy, shutting out questions about her family.

Whatever happens, she says, being a mother remains her highest priority.

"I knew I wanted children in my life. The acting was always in relation to it. Life at home is chaos. They're wonderful. They're such interesting human beings. I just love it."

And then she adds: "I'm lucky."

"I wanted children in my life. The acting was always in relation to it," says Bening, the mother of four and star of "Being Julia." In "Being Julia," Bening plays an stage actress in 1930s London who falls in love with a younger man, played by Shaun Evans."You've got to make peace with it," Bening says of her fame as the wife of Warren Beatty (shown above at the Hollywood Film Festival last week), whom she met when they starred together in 1991's "Bugsy," below.Bening as chilly real estate agent Carolyn Burnham in "American Beauty."