Ms. Kirshner, who is 29 but looks younger, is frail and mysterious. Her character, who shares air time and episodic drama with at least six others, each with her own tics and emotional baggage, is the one who carries the heaviest psychic weight of the series.

"She's utterly impulsive," Ms. Kirshner said recently over a leisurely lunch at Pastis in Manhattan. "She's a very despicable character who lies, cheats, is selfish, indulgent and so terribly truthful, too. How can you like her? She's evil." Then she added, "I'm nothing like her."

"I actually think that for me it's always less about sexuality," she said about her role. "It's more about the political and social implications. It's scary, especially when you're someone who gravitates toward darkness like Jenny does. What I know about her until now is that she's so unbelievably lonely."

She leaned forward in her banquette to make the point. Dressed in a black skirt, black tights and a black lacy blouse, her pondlike green eyes recording everything around her.

Ms. Kirshner seems to have popped out of nowhere, one of those overnight starlets who show up on "The Tonight Show With Jay Leno" and are featured in glossy magazines. But she's been around for 15 years and has appeared in 24 films, including "Party Monster" and art-house movies like the sexually provocative "Exotica," directed by Atom Egoyan and made when she was 16.

Her father, Sheldon Kirshner, gave her career a boost when he signed permission for her to appear in a film where there was nudity. Looking back at "Exotica" and other sexually explicit roles she has done, she said, "I didn't know what I was doing." But her ability, and willingness, to play such risky roles at a young age, she added, freed her, too.

In "The L Word," one of the boldest shows on television today, Ms. Kirshner's Jenny plays the hottest sex scenes, with Karina Lombard, who plays Marina. Caught between two sexes, between the labels gay and straight, Jenny veers madly, unpredictably. Her role has also made her a pinup for thousands of lesbians.

Sex scenes with women are "more fun and easier," she said. "It's nothing to be ashamed of. I genuinely feel that way, and I think that women are lovely and generous. There's an intangible feeling and a comfort level that is beautiful."

So the question is obvious. She's been fending it off for months with that inscrutable sly look of hers. "People feel the need to state their sexuality, almost defensively," she said, rather opaquely. "I understand the reason, but it shouldn't matter, and it doesn't matter."

Then, speaking of "The L Word," she said: "It shouldn't be considered a gay show, because it's beyond that. It's about people's lives." She added, "I don't care if people think I'm gay. Gender is of no consequence to me. It's a person's brain that counts."

Aside from her acting, she is working on a book about her travels to some of the world's violent spots. During the last two years she has visited Ciudad Juaréz in Mexico, where a culture of violence has claimed the lives of at least 400 women in the last 10 years; the Thailand-Burma border, where guerrilla warfare and corruption have penned thousands in decrepit camps; Haiti; and Cuba. She said she planned to publish the book in Canada in 2006 but hesitated to talk about it.

"I'm embarrassed," she said, her hands fluttering over her face, one of the many apologies she makes for being successful, for being who she is. "It's such a cliché, an actor going around to these awful places."

Still, bringing out an envelope, she wrote down the title of the book, "I Live Here." She described the work as part graphics, part photography, with text written or spoken by the women and children in those camps. She's visibly moved talking about it, but she wants to make clear she does not see herself as any kind of hero. "I don't have aspirations to go out and be a champion of the poor or anything like that," she said.

Born in Toronto, Ms. Kirshner is a granddaughter of Holocaust survivors. Her father, a journalist who works for The Canadian Jewish News, was born in a displaced persons' camp in Germany in 1946. He met her mother, Etti, a Bulgarian, in Israel. Mia is the older of the couple's two daughters.

"The only books in my house when I was growing up were about the Holocaust," she said. "That's all I read as a child. But I never knew about my family's experience." It was not talked about in her home, but "I think it shaped who I am."

Isolated and timid, she went to a school where most people were blond and rich, she said, and there she was, wearing second-hand clothes, dark-haired and Jewish. She moved to Los Angeles when she was 22, got an agent, worked hard from audition to audition. "So many rejections!"

And then came "The L Word."

"I've been looking for Jenny for a long time," said Ms. Chaiken, the show's creator, in a phone interviews from Los Angeles. She found Jenny on a videotape Ms. Kirshner made as a tryout for the show. "There was Mia, and she was just stunning," Ms. Chaiken recalled. "She has that riveting beauty that is unlike anyone else's, and she was so deep and intense."

Ms. Chaiken, who struggled seven years to bring "The L Word" to the small screen, said she was looking forward to the show's next season, which she will begin to tape in June in Vancouver. She said she would keep the audience guessing about Jenny's sexuality. "I think that sexuality is fluid," she said. "Jenny's sexuality definitely exists on the edge of fluidity. She will be mostly with women, but with some men, too."

There are no boundaries to what Ms. Kirshner can do as an actor, Ms. Chaiken said. "I see her having such a great range. I do see her as a leading lady, though I think she's a challenging leading lady. She's not the usual. I can see her in an Almodóvar movie or being chosen by Alfonso Cuarón."

Leisha Hailey, who plays the bisexual Alice in the show and was Ms. Kirshner's roommate during its taping in Vancouver last year, raves about Ms. Kirshner. "We lived together, we got to see each other morning through night, and for some reason, Mia and I love coming home to each other."

Ms. Kirshner "has a unique way of capturing emotions," Ms. Hailey added, "and I find it fascinating, and all these years to come, I'll be learning from her as an actress."

Ms. Kirshner said she was decidedly unimpressed by the glamor of her profession, calling acting a job like any other. She recalled a day several years ago when, on a tour to promote "Exotica," when she found herself in a luxurious hotel room in New York yet felt terribly alone.

"That life of hotel to hotel, from set to room," she said, "that's not a whole life."

Photo by Sara Krulwich/The New York Times