September 1, 2004 | Many American actresses might think twice, or even thrice, before signing on to play Becky Sharp, the upwardly mobile anti-heroine of William Makepeace Thackeray's Vanity Fair.

But Reese Witherspoon wasn't fazed by the burden of audience expectations. And after mastering an English accent for Oliver Parker's 2002 film of Oscar Wilde's The Importance of Being Earnest, the Nashville-raised actress was confident she could once again pass muster as a famously British character.

So she accepted almost immediately when Indian-born director Mira Nair (Monsoon Wedding) called to offer her the lead role in a new adaptation of Thackeray's classic novel.

"I'd just finished Legally Blonde 2," Witherspoon said at a recent Manhattan press gathering. "And while that was a lot of fun, I always try to look for something really different after every film I finish. Mira Nair and I had met two years earlier, just to talk about projects - I loved her work, and I thought she'd be a great person to work for. And I'm also very interested in working with female directors and other women in the business."

When she received an early draft of the Vanity Fair script, "I was blown away by it," Witherspoon said. And when she later received the final rewrite by Oscar winner Julian Fellowes (Gosford Park), "I was blown away even further."

But before she could fully commit to the project, Witherspoon admitted with a mischievous smile, she had to find out just how much Nair really, really wanted her to portray Becky.

"I called up Mira and asked her: 'Can we do this movie while I'm pregnant?' She said, 'Well, yeah. OK. When were you thinking about getting pregnant?' And I said, 'Actually, I'm already about four weeks pregnant, so we'd better get going.'"

No problem: Nair had already done sufficient pre-production planning to start shooting a bit earlier than originally planned, and to continue at an accelerated pace. To be sure, the director and her collaborators - including cinematographer Declan Quinn and costumer designer Beatrix Aruna Pasztor - had to devote much of their energies to disguising the slow, steady burgeoning of their leading lady. But during one key scene, in which a very pregnant Becky Sharp cuddles with Rawdon Crawley (James Purefoy), her war-bound husband, Witherspoon proudly displays a full belly along with a beaming smile.

"The great thing about working with Mira," Witherspoon said, "and the reason I was so attracted to her work in the first place, is that she has this way of putting sexuality in her films that's not gratuitous, not overt. It's a very female sensuality. It's hard to describe, but it has a lot to do with color and mood and lighting. So I felt very comfortable with her. When she told me, 'I want to make sure we make the most of your body, and show your pregnant belly,' I didn't feel nervous at all.

"Well," the 28-year-old actress added with a giggle, "OK, on the day we filmed that scene, I did feel a little bit nervous. But I knew Mira would do it in a very beautiful way. And I was very happy when I saw how it came out in the film. It adds to the vulnerability of the character.

"I mean, if the character actually has any vulnerability."

Remaining faithful to the spirit of Thackeray's sharply satirical masterwork, Witherspoon plays Becky - a low-born orphan who purposefully employs brains and beauty to advance in 19th-century British society - as one of the most dazzling and dynamic social climbers to grace the screen since Scarlett O'Hara dreamed and schemed in Gone With the Wind. Which, when you think about it, is altogether appropriate: Many literary scholars insist GWTW novelist Margaret Mitchell must have been inspired by Vanity Fair.

Witherspoon -- who gave birth to daughter Ava, her second child with actor-husband Ryan Phillippe, shortly after Vanity Fair wrapped - isn't bothered by critics who question the appropriateness of her being cast as Becky.

"I definitely think that being an outsider, and being the only American in the cast, really helped inform things for me," Witherspoon said. "Also, coming to a piece of literature like this, that is so revered and steeped in history, and people know it and they know the characters - it was nice to be able to come to it with a fresh perspective. And it was nice coming to it with Mira, who also feels like an outsider, being on the outside of that culture.

"And I think that's how Thackeray would want it. I think people who put their ideas out there want them to be reinterpreted from time to time, and brought to a modern audience from a perspective that everybody understands. And I think everybody understands being an outsider."