When Christine Lahti was asked to take over the title role in the Pulitzer prizewinning Broadway play The Heidi Chronicles, her first reaction was, "How wonderful to be offered a part where you never leave the stage." But on second thought, she was uncomfortable with the play's last scene, in which Heidi, the hard-core feminist, has a meltdown over the daughter she has adopted in midlife. "I thought the baby absolution ending seemed too pat," Lahti recalls. Her convincing argument led playwright Wendy Wasserstein to add a line making it clear that although Heidi was a single mother, she also had a satisfying relationship with a man. "So it wasn't just the baby that filled her life now," says Lahti. "There were a lot of things she was able to commit to—a relationship, her family, the baby, an apartment, as well as her friends and career."

Lahti's comfort with that new ending is easy to understand: It closely parallels the developments in her own life. At 39, she's a nearly new mom with a 17-month-old son, Willie, and a solid six-year marriage to director Tommy Schlamme. And, like Heidi, Lahti has found success in the work she loves. More than success—this week she's a triple threat, with roles on Broadway, television and at the movies. Lahti can be seen not only as Heidi's distraught feminist but also as the stern medical professor who slaps a wisecracking student (Matthew Modine) into shape in the movie Gross Anatomy. This Sunday (Dec. 3), she also stars as a blue-collar mother of two forced into homelessness in the CBS movie No Place Like Home. Not one of the roles qualifies as typecasting—and indeed, one key to Lahti's success is her ability to slip quietly, unobtrusively into a wide range of characters. "There's a comfort level about Christine," says No Place Like Home director Lee Grant. "There's an ability to identify with her. She can be beautiful and still live on your block."

The block Lahti inhabits in Grant's project, though, is one condemned by bad luck and unspeakable pain. To prepare for the TV movie, she visited mothers in several New York City welfare hotels. One day, she recalls, she went to lunch with 12 members of a welfare women's group. "I was asking them all sorts of questions, then one woman asked me, 'Do you and your husband in the film argue much?' and I said, 'Oh, yeah,' " relates Lahti. "Then another woman asked how I was going to wear my hair. 'It would be great if you had bangs,' she said. 'That way when your husband hits you, your hair would fly, and that would look kind of nice.' " Lahti was shaken by the suggestion. "It dawned on me," she says, "that this woman's immediate connection to arguing was violence. I realized what a different world I was entering."

With The Heidi Chronicles, such a grand leap wasn't necessary. "The play really pushes a lot of buttons in me," says Lahti. "Christine has Heidi's dignity," says playwright Wendy Wasserstein. "She's a healthy girl from the Midwest, and she really understands the journey Heidi takes from that first scene at the high school dance."

Lahti's own journey began in Birmingham, Mich., where she was raised the third of six children of Paul Lahti, a surgeon, and Elizabeth, a nurse turned housewife turned painter. Christine says she developed her flair for the dramatic while trying to stand out from the crowd of her brothers and sisters. She went on to study drama at the University of Michigan, beginning school as a well-coiffed sorority member and leaving, like Heidi, in the late '60s as an unshaven and unshorn hippie. "Women's groups really had an effect on me," Lahti says. "The woman's movement changed my life."

But despite her disheveled appearance, Lahti was an early convert to the '80s hard-work ethic. Moving to New York City in the early '70s, she picked up a few commercials (in one for dishwashing liquid, she whispered sweet nothings to a plate) and, finally, a part opposite Al Pacino in 1979's...And Justice for All. "I'm tall, so I got to play doctors and lawyers," says the 5'10" actress. In 1981 she put on a white coat and tended to Richard Dreyfuss in the movie Whose Life Is It Anyway?

In the years that followed, Lahti gained a reputation as something of a scene-stealer, walking away with Goldie Hawn's Swing Shift (1984) and Mary Tyler Moore's Best Friends (1986). "When two women are involved, people automatically make it a contest," said Christine at the time, bristling at rumors of a cat fight when she, not Goldie, was nominated for a Swing Shift Oscar. "Acting isn't about winning." On the other hand, she had to confess she enjoyed the attention: "It's flattering." The flattery led to starring roles as an eccentric drifter placed in charge of two teens in 1987's Housekeeping and a radical on the fly from the FBI with her husband and children in last year's Running on Empty.

On July 5, 1988, Lahti began experiencing motherhood firsthand when Willie was born on location in Jackson, Miss. This time, however, it was Lahti's director husband who was making the film—Miss Firecracker. "I went down to Jackson in my ninth month of pregnancy," says Lahti. "I was in 93 degree heat with 100 percent humidity, so he owes me one." Besides, if she hadn't gotten pregnant it would have been she, not Mary Steenburgen, who played the co-starring role. "I wasn't actually offered the part, but he is my husband," she says.

Now Schlamme's looking for another movie that they can do together but, teasing, he says that it may not be for the reasons she thinks: "If I find another movie and she's right for it, she'll get pregnant again, and I want to have more kids."

Except for a month in Pittsburgh for No Place like Home and a month in L.A. filming Gross Anatomy, Lahti has been able to stay in New York City with Willie. "That's one of the reasons I decided to do the play," she says. "I wanted to be in one place with our family intact." Any free day she has, they slip away to their new farm in upstate New York.

Sitting with Willie on her lap, Lahti looks around the six-room apartment and reflects on how her life turned out differently from that of her stage counterpart. "I got married—though there was a time I wasn't sure I ever would. I entertained the idea of buying a brownstone with a bunch of women and maybe raising children with them. It didn't work out that way. Thank God."