Even if griping yuppies give you the big chill, count on Mel Harris to melt down your resistance. As the star of ABC's new season hit thirtysomething she cuts to the heart of a character who might otherwise seem a spoiled brat. Harris plays Hope Murdoch Steadman, an overachiever whose career in publishing has been sidetracked by motherhood. Hope is confused about what to do with the ambition that used to fuel her life. Cranky from staying up nights with a bawling infant, she frets about her husband's roving eye and about losing old friends who can't adapt to her new schedule. Well written, literate and realistic, thirtysomething is as refreshing and unassuming as 10-month-old Lacey and Brittany Craven, the twin tots who take turns playing Hope's life-changing infant.

One critic predicted that the show would raise "a collective cry among thirtyish couples across the land: 'Just like us!' " It sure did with Harris. After reading the original script by the show's executive producers and writers Marshall Herskovitz and Edward Zwick, Harris stormed into their offices and demanded, "How long have you been living with me? And how come no one's told me?" Though she's been separated for three months from her husband of four years, photojournalist David Hume Kennerly, Harris claims to have lived through many of the show's crises. She and Kennerly are parents of a son, Byron, 3. "The situations you go through as parents," she says, "remain common to everyone."

Her "willingness to bring her own life to the part" helped Harris get the job, says Herskovitz. "When women were reading for the role, it was very clear who was a mother in real life and who wasn't." Herskovitz adds that she's also "sexy and beautiful. You look at Mel and want to keep on looking." Mel, 31, modestly demurs. "I'm okay, that's it," says the lanky (5'8") model-turned-actress. "I have no interest in being a star. I'm a hard worker and a hard player—that sums me up as a person."

Though her TV character is a stay-at-home mom, Mel was back at work modeling nine months after her son was born. "So Hope's a lot sweeter than I am," she says. Don't mistake that retort for guilt. "My son and I have a very good relationship," she says. They play baseball, watch videos and cook brownies together. (A live-in nanny cares for Byron while Mel is at the studio.) "Some people ask me, 'How can you work and not be with your kid all day?' Well, I asked my son's first nursery school teacher, 'How can you be with these kids all day?' That doesn't mean I don't love my son."

Byron's toys and playthings are scattered throughout Harris' two-story, two-bedroom home in Beachwood Canyon, a stone's throw from the Hollywood sign. The house is casually patrolled by a friendly Irish setter named Mulligan, Mugs for short. An impressive display of photographs graces the walls, some of them by Kennerly, 40, a Pulitzer prizewinner who was President Gerald Ford's White House photographer. In their years of marriage, she accompanied him on assignments to dozens of foreign countries. She recalls being chased by wildlife in Kenya, bargaining at an ancient bazaar in Damascus and hearing artillery shells bursting above her during a 1983 visit to Lebanon. Through Kennerly she came to know and admire the Fords—their daughter, Susan, says Mel, remains "a close friend"—and other world leaders. Jordan's King Hussein and his American wife, Queen Noor, once flew Mel and David to Aqaba for an impromptu visit.

Kennerly may have moved two months ago to a house across the canyon, but Mel's place still resonates with memories of the marriage. "It's different not having David here," admits Mel, the subject obviously a delicate one. Kennerly says Mel is a "wonderful mother and wife" and blames himself for the split. "Mel tried harder than I did. I'm just a lousy husband. I don't give good marriage." Mel finds it more difficult to articulate her feelings. "Our trying to live apart is relatively new," she says, "and I don't know what to say." Still, she makes it clear the problems with her marriage run deep. "I'm not a believer that people should stay together for the children," she says. "I don't think it's healthy to live in a household full of fight and anger."

She learned that the hard way. Born in Bethlehem, Pa., and raised in North Brunswick, N.J., Harris says that her parents' home was loveless long before their divorce in 1969. Mel, the third of four children, says her father, a football coach at Princeton, and mother, a high school science teacher, were "better off" after they parted.

During her high school years in New Jersey, Mel (so called by her baby sister who couldn't pronounce Mary Ellen) acted in many plays. Her older sister, Delores Lobbato, 39, remembers her as "very determined. Mel had a lot of guts moving to Manhattan at 17, trying to be a model." Actually she intended to study pre-law at Columbia University, but she deferred that plan until she could sock away tuition by modeling. Signed by the Wilhelmina agency, she did ads (Revlon, Almay) and TV commercials (TAB, Noxzema), soon deciding the law couldn't make her as satisfied or solvent as modeling.

For eight years, Harris took acting lessons without doing a single audition. Confidence came just three years ago, when she and Kennerly moved to Hollywood. On her debut TV tryout, she triumphed over hundreds as a one-shot romance for Bruce Willis on Moonlighting, only to have the producer eliminate the role before she ever faced the cameras. She moved on quickly to TV guest shots (The Wizard, Alfred Hitchcock Presents) and last year landed a movie, Wanted Dead Or Alive. Knowing that thirtysomething is her major shot at success makes Mel anxious. "I keep waiting for the bosses to say they meant to hire somebody else."

Not likely. Harris already has a five-year contract. That should put an end to her worries for a while. "Are you kidding?" she asks. "I have plenty of insecurities: Am I a good-enough mother? Do I take proper care of my dog? Should I go to church?" Then there's her social life. Or, as Mel describes it, "what I can fit in at the end of 14 hours at the studio and coming home and putting my child to bed." But, hey, don't accuse her of whining, as her character sometimes does on thirtysomething. "There are people I'm seeing," says Mel, brightening. "I'm not sitting home knitting."