Some nights when Erika Bogren is sitting downstage in the middle of "My Sister in This House," all of 15 years old, honey-blond hair and braces, she can hear people in the audience say, "Oh, she's so cute!"

She loves that moment.

"I want to say," she whispers conspiratorially, narrowing her eyes, " 'Wait until the end.' "

By the end of this tense, mesmerizing play about two sisters who are housemaids to an imperious Frenchwoman and her daughter, Erika Bogren has probably stunned her audience. As the younger maid, Lea, she has a strange, incestuous relationship with her older sister, Christine; and the two end up murdering their employers. The play, Studio Theatre's season opener (scheduled to run through next Sunday), is so intense that the actors hug each other during the curtain call to reassure the audience.

For Bogren, the role of child seductress/murderer is a departure from parts she's played in her two years as a professional Washington actress, and it is a surprisingly gifted performance for one so young. Playwright Wendy Kesselman, whose play is based on murders that happened in Le Mans, France, in 1933, calls the casting of Bogren "daring."

"It's really surprising to hear what people say afterwards," says Bogren who is breezy, animated, and unself-conscious sitting in her family's Kensington home. "Some people are like, 'I think you're too young to play that role . . . It's not you.' I'm like, 'Of course, it's not!' It's a part. I'll probably never find a part that hard. It's so challenging."

The part calls not just for a physical intensity a very young actress might not be able to muster, but also for a painful, quiet awkwardness that is uncharacteristic of Bogren. "It's hard for me to stay still," she says. "That's still the hardest thing."

It's not until late in the play that the most explicit moments arise between Lea and Christine -- who is stunningly played by Sarah Marshall -- including dimly lit, silent kissing scenes between the two. Bogren says the more sexual overtones of the play didn't hit her on first reading. "I didn't pay any attention to the stage directions at first," she says, "so I didn't really know . . . I was surprised: 'Uhmm, when did this come about?' "

So there was an initial awkwardness to dissolve.

"The first thing that helped immensely was that Sarah and I were friends right away," Bogren says. "We're good friends right now. If it was someone I was not close with, it would be kind of weird. It's the kind of thing that's hard, but it's challenging more than hard . . . It's part of the play, it's part of the character and without it, that item that Sarah and I have, the play might not be as strong. That makes our relationship a big factor in the murder."

Joy Zinoman, artistic director of Studio Theatre and the play's director, worried about getting Bogren comfortable with the more sexual scenes. "When we first talked about the motivations and the sexual things, her first reaction was, 'Oh, that's gross.' " But they simply went through the scenes line by line, action by action, and "then the fifth time, I'd say, 'Now kiss her,' and she'd do it. And we didn't talk about it much."

Zinoman also knew from the moment she read the script that she wanted to cast Bogren, who had appeared in "5th of July" -- her first professional stage appearance -- and "Member of the Wedding" at Studio. Zinoman says her youthfulness adds vividness to the role: "I think what we get out of it is this awful victimization. Worse than with an older actress who knew what she was doing. I find this more poignant in a way."

Bogren remembers discomfort fading as rehearsals went on. "It took a lot of work," she says, "and just finally saying" -- she sighs hard -- " 'who cares?' . . . [At first the intimate scenes] looked awkward. It just looked stupid. I mean, why do it if it really doesn't look the right way it should? And then it was no big deal, really. We talked about it, me and Joy. If you're an actress, there're things you have to do. Always. One day, you may be asked to run around the stage naked." She giggles.

Would she?

"No," she laughs. "I don't know about that."

In most ways, Erika Bogren is a typical 15-year-old. The school bus stops at 7 a.m. in front of her home. She's a grouch at that hour, she says. But consider her schedule: Her first class at Walter Johnson High School in Bethesda is at 7:30, and she's home by 3 p.m. She sees friends, watches TV, does homework -- and then she's off to the theater at 14th and Church streets by 5:45 for an 8 o'clock performance, driven and picked up by her parents. When she comes home at 11, she's still restless, so she pads around the kitchen fixing herself food, maybe squeezing in homework before falling asleep to the lullabies of WKYS.

On weekend nights, Bogren joins the cast members at Trio's or Stetson's or other favorite haunts. "They drink beer, I drink Perrier," she says.

She makes her own decisions about her career, but she was commanded by her mother to clean her room before an interview. "I said, 'Why not let her see the real me?' " Bogren imitates her mother's response: 'Clean it!' " On a bookshelf are Nancy Drew books, and on a cupboard top is a stack of Vogue magazines. There is a plant -- an opening night gift from her father -- and swimming awards from community pool teams. Under her stereo there is a copy of the Riverside Shakespeare, a gift from the cast members of "5th of July" who all signed it. "It's my favorite book," she says. "I can't understand it all. I guess one day I will."

The New Yorker cover poster featuring New York as most of the country hangs on her wall. "I want to be on Broadway one day," she says. "To me, it's so much more of a challenge to be on live stage. For me, famous isn't important. It's the idea that you've accomplished something."

Bogren is three quarters of an inch short of five feet tall (her description) and weighs 75 pounds, eats whatever and whenever she likes.

She's never taken an acting class -- though she wants to -- and doesn't really know the techniques the other actresses use to warm up before the play. Bogren amuses herself by walking barefoot down the banister on the set or jumping from the second-story bedroom set to the dining room below. "I'm a daredevil," she says. "They all get mad." Sometimes she'll bring her homework along, or a sketchbook for drawing class.

Her $75 a week pay is "fine," she says. "I'm a kid. I don't really care. I've done plays without money. It really doesn't matter to me either way." She spends it all on clothes. "I should put it in the bank," she laughs, "but Bloomingdale's calls." She is wearing $56 Guess jeans.

She looks younger than her 15 years. She has worn braces for two years and has one request of her orthodontist: "Please have them off by senior prom." One night, in a scene in which her older sister has to put her lace-gloved hand over Erika's mouth, the glove got stuck on Erika's braces. The two managed to disentangle it, struggling to keep straight faces.

Her husky voice gets nasal as she keeps talking -- the result of adenoids, she says, that must be removed. Her conversations are animated and slightly breathless, dotted with typical post-valley-girl-isms. ("I liked 'Risky Business,' because Tom Cruise is too cute.") One inadvertently slipped into the play. There is a scene in which Bogren must accidentally knock over a pewter pitcher. "You can't believe what I said one night," Bogren relates. "I go, 'What will Madame do? She'll kill us for sure!' " Bogren snorts with laughter. "When we got offstage, Sarah's like, 'FOR SURE?! Erika! That's awful!' "

But Bogren's youth and charming irreverence do not obscure her savvy and ambition. She wants to be in any film version of "My Sister in This House." There is one role she's dying to do: "I want to be Helen Keller." She means she wants the role of the young Helen Keller in "The Miracle Worker." "I want to do that play one day before I get too big."

Her father, Peter Bogren, remembers when his daughter was 10 and doing gymnastics. "I asked her how she was enjoying it, and she said, 'Well, I'd really rather do some acting,' " he says. "I said -- typical parent -- 'Well, what are you going to do about it?' The next day she had called the Children's Radio Theatre."

Erika Bogren remembers that, too: "I called them up, and I said, 'This is Erika Bogren, and I know you'd like me to audition for you so when can I come in?' "

Her father recalls his conversation with his daughter after she auditioned for "5th of July": " 'How'd it go?' I asked. She said, 'Well, I don't know. But I know what I want to do with the rest of my life.' "

She also appears to know what it entails on stage and off. Peter Bogren, 50, who works in public relations and advertising for the insurance business, remembers picking her up after a performance of "Grown-Ups," the Source play she was in this summer. "I knew she hadn't been feeling too well," he says. "It was press night, and there were a lot of people around. I picked her up and said, 'Let's go home.' She said, 'Wait, there're some things I've got to do.' And she went around, shook hands with the press people, said a few words. I thought, 'Jesus.' Then she finished that about 15 or 20 minutes later. I put her in the car. She went to sleep."

Joy Zinoman consulted the Bogrens about Erika's role in the Kesselman play: "I told them there was lesbianism and child abuse, but I didn't think that's what the play was about."

Peter Bogren remembers, "I said to her, 'Hey, if you think she can handle this, fine.' " He says he liked the play. "The acting is awfully strong."

Lois Bogren has a slightly different perspective. "I was telling my sister that I was extremely proud of her, but it's not the type of role a mother likes to see her young daughter play," she says, chuckling. She is 40 and the director of marketing for Balfour Supply Service in Rockville. She made sure that her daughter's school counselor knew about this play. "And if she was having any problems at school, I wanted to know," Lois Bogren says. "School is still very important."

"It's kind of her show," says Peter Bogren. "I guess the next thing we'll come up against is college." The Bogrens have a son, Scott, 18, who is a freshman at Indiana University.

One of the difficulties of her new career is what Erika must give up, her mother says. "All of her friends convinced her to go out for homecoming princess, but no way can she do it. Homecoming dance is the same night as the play. So she realizes there are some things she has to give up."

"I'm really bad," Erika Bogren sighs. "I try and do 100 things at once. I'll try and be on the swim team, I'll try and do a play, I'll also try out for the play at school."

She wants to explore films and commercials. "I guess I need an agent, but I don't really know one," she giggles.

She's learned a lot already. Technical directions mystified her when she started working with Joy Zinoman. "She used all these words I didn't know," Bogren says. "Words like 'motivation' and 'transition.' I knew what they were, but I didn't know they were called those words. And she always used 'profound' and 'yeoman.' So I wrote her this card. It said, 'Joy, this has been a very profound experience, a yeoman experience, which has motivated me to many levels and transitions.'

"She said, 'You did it!' "