NEW YORK - If Maggie Gyllenhaal were a superhero, she'd combine the power of strength with invisibility.

The actress, 30, has opted for an existence that's removed from Hollywood and Manhattan, living in Brooklyn with her fiance, Peter Sarsgaard, 37, and their daughter, Ramona, who turns 2 in October. She walks around in nondescript clothes, pairing a gray jacket with a loose skirt, her hair pulled loosely away from her face. Photos of Ramona were never sold to any magazines, and the little girl is rarely photographed out, despite hitting local playgrounds and parks with her parents.

"We do our best, but it's very difficult," Gyllenhaal says of shielding her toddler. "You do the best you can. (But) they still find you."

She could become easier to spot after her co-starring turn in "The Dark Knight," out today, one of this summer's most awaited films.

Gyllenhaal takes over for Katie Holmes, who appeared in 2005's "Batman Begins," as Rachel Dawes, Gotham's ambitious, nattily attired prosecutor who's torn between DA Harvey Dent (Aaron Eckhart) and Batman himself (Christian Bale). Gotham, meanwhile, is being terrorized by a demonic, disfigured criminal: The Joker (Heath Ledger).

"Dark Knight" looks likely to vault Gyllenhaal, often dubbed the art-house princess for her long list of edgy films (2006's "World Trade Center," "Stranger Than Fiction," "SherryBaby"; 2002's "Secretary"), into a stratosphere of stardom she's not so sure she wants.

The film is Gyllenhaal's first bona-fide behemoth of a movie, a prospect that leaves her a little leery.

"I really didn't know if I wanted to do a huge blockbuster," she says. "And I don't think I realized how big it was going to be. I'm really proud of the movie, to be a part of something really great. When you see 'Dark Knight,' you see that it's in no way a compromise."

That's no surprise to directors who have worked with her.

She's "a powerful actress, original, different," says Oliver Stone ("World Trade Center").

"She's one of the most original and most talented actresses of her generation," says Marc Forster ("Stranger Than Fiction"). "She's very much in the moment and captures the moment in a three-dimensional way."

Unlike other stars with careers poised to hit the big time, her instinct is not to jump right into it. It's to pull back. Once she's done promoting the film, she says, "I'm going to try and hide out a little bit."

When it came to her "Dark Knight" role, she was the furthest thing from passive. She met with director Christopher Nolan in Los Angeles to discuss what made the character tick. They swapped ideas, and she talked about how she saw Rachel. And then she landed the holy grail: an actual copy of the script.

"It was a big deal. This guy sat in my driveway the entire day. I was a new mom and it was a really long script, and I was trying to do other things while reading it," she says.

"I had a lot of ideas," she adds. And when talking it over with Nolan, "I was very clear that I didn't want to be arm candy. He was so receptive, so interested."

Nolan says that Gyllenhaal was a natural choice "because she has the kind of natural drive that I thought the character needed. She isn't the type to show up and read lines. She has specific ideas about her character, and isn't afraid to bring them up."

The 1999 Columbia University grad, part of the Gyllenhaal filmmaking family (mom is screenwriter Naomi Foner, dad is director Stephen Gyllenhaal and her brother is actor Jake), wanted Rachel to be smart, outspoken and a solid presence.

Eckhart calls her "a strong personality. She has very distinct ideas about her character. She has opinions, a lot of energy and is not a pushover."

Anyone who has spent time around the actress can attest to her strength of will. She has been known to berate tabloid reporters for working for publications that stalk her and her daughter.

She's more circumspect when it comes to Ledger, who died of an accidental drug overdose in January. Gyllenhaal recently saw "Dark Knight" for the first time, but she isn't one to share any intimate memories of working with Ledger and has been critical of the circuslike coverage of his death and funeral. But she does say that watching him on screen left her "really emotional."

"In the middle," she says, "you sort of get lost in him being The Joker. I felt like someone could hate this or love this, or think it's a wrong choice or a right choice, but really there's no way to qualify it. Sometimes in my work, you're just alive and being the person you're playing. It's unusual. It's difficult to get there. And I think Heath did. Nothing Heath could do was wrong."