Michelle Williams doesn't act - or dress - like a movie star.

Wrapped in a rather homely quilted jacket on a cool and rainy day last May at the Cannes Film Festival, Williams exudes comfort rather than style - in stark contrast to glamorous contemporary stars such as Angelina Jolie and Nicole Kidman, who always look Vogue-ready.

At only 5 feet 4 inches, the 30-year-old Montana native seems pixieish at first. But when she starts talking about the craft of acting, it becomes clear that she's as tenacious as Barbara Stanwyck, as quietly intelligent as Sissy Spacek.

"I've been involved in this project for six years," Williams says of her latest movie, "Blue Valentine," which opens today in Austin and screened at Cannes in May. "I really wanted to get this project made because I think it's a great exploration of intimacy."

Williams plays Cindy, a young woman who gets pregnant and can't go through with a planned abortion. Instead, she marries her new boyfriend, Dean (Ryan Gosling), who is not the child's biological father.

Although she loves her daughter and admires the playfully affectionate bond between the child and Dean, she "feels trapped," Williams says. It's a raw, emotionally naked role in a heartbreaking movie.

"The problem for Cindy is the force of the past," she says. "She's never gotten to experience herself, to grow. It's like she's holding her breath."

And living with Dean isn't exactly conducive to personal growth. Although charming in his own way, Dean likes to drink beer in the morning, then a few more in the afternoon before settling in for an evening of imbibing.

And when Cindy asks whether he ever has aspirations to be something other than a house painter, Dean responds that he feels quite lucky to have a job where he can drink beer in the morning.

Williams says she sees the movie as a question, echoing director Derek Cianfrance's reference to the song "Where Did Our Love Go?"

"Cindy loves Dean's affectionate side, but she realizes that she needs something more," Williams says. "She needs to understand her soul. So she struggles with the question of `How do I leave this guy?' "

Throughout the discussion in Cannes, Williams avoids any reference to her private life - or the fact that she, too, has been raising a child without a father since Heath Ledger died of a prescription drug overdose in 2008.

The two became romantically involved while filming 2005's "Brokeback Mountain," but were separated before his death. And the parallels of Williams' real life to Cindy's fictional home life in "Blue Valentine" are evident.

But Williams declines to discuss anything about Ledger, saying only that "it's a matter of privacy."

The implication throughout the interview is clear: that she's much stronger in her professional life than she is in private.

That kind of vulnerability will serve her well in her new role as Marilyn Monroe in next year's "My Week With Marilyn."

The movie, being directed by Britain's Simon Curtis, deals with the filming of 1957's "The Prince and the Showgirl" and Monroe's relationship with co-star Laurence Olivier.

She'll be in heady acting company. Kenneth Branagh plays Olivier; Julia Ormond plays his wife of the time, Vivien Leigh; and co-stars include Emma Watson, Judi Dench, Derek Jacobi, Dominic Cooper and Dougray Scott.

It seems like a role Williams was born to play.