For 19-year-old Jennifer Jason Leigh, the irony isn't that her first really meaty role requires her to starve, but that she got it only because the Yale campus turned out to be Fat City for Jodie Foster. Originally slated to star as the victim of anorexia nervosa (the psychological disease of self-starvation) in ABC's The Best Little Girl in the World, Foster snacked through her first college semester. Indeed, by a week before the scheduled start of filming last December, Jodie was 20 pounds overweight. Exit Foster, enter Leigh, who says, "I wanted the role so badly I would die for it."

Or at least diet. Normally packing 104 pounds on her 5'3" frame, Jennifer dropped to a wraithlike 86 pounds during filming and briefly developed anorexic symptoms. "I'd lie in bed and count my ribs," Jennifer remembers. "I'd look in the mirror and say, 'I'm fat. I have to slim down.' " The sometimes fatal malady, suffered by a growing number of young women in the U.S., once afflicted Jennifer's best friend. "She dropped to 54 pounds and was falling down all the time," says Leigh. "Once I saw her taking a shower—her body looked like a deflated balloon." The girl survived, but an anorexic young woman who served as adviser on Best Little Girl was less fortunate. Despite five years of medical treatment, she died of shock last July at 22.

Jennifer isn't really threatened by anorexia, which is often triggered by the sexual and emotional pressures of adolescence. "Being a good girl means suppressing a lot," she says. Like maybe her relationship with actor David Dukes, who co-starred with Richard Gere in Broadway's Bent last year. "He's supportive, giving, brilliant," Leigh gushes. He is also, at 35, nearly twice her age. Says Dukes: "It's the first time I've gone out with anybody under, well, under 26—and Jennifer looks 12!" The match-up makes for some strange mix-ups—especially when they socialize with Dukes' 15-year-old son, Shawn. "Once, when we were dining out with Shawn, another couple in the restaurant was giving me benign smiles, like parents give other parents when they're out with the kids," Dukes recalls. "Well, Shawn went to the men's room and Jennifer leaned over and kissed me—not at all like a father-daughter kiss—and the other couple looked horrified."

All that aside, Jennifer says she resembles her TV character as "a 'perfect little girl' from a middle-class, successful family." The daughter of actor Vic (Combat) Morrow, Jennifer grew up in her mother's Hollywood mansion after her parents divorced when she was 2. Mom is screenwriter Barbara Turner, who has a movie, Freedom, on ABC next week based on the turbulent coming-of-age of Jennifer's older sister, Carrie. Leigh seldom sees her father. "It was a weird situation. He never called me, I never called him," she says. "I respect Vic as an actor. I just don't know him. He's a stranger." Jennifer, a Palisades High School dropout, has been acting since 14, and her credits now include the TV movies Angel City and last March's The Killing of Randy Webster, as well as the current thriller Eyes of a Stranger with co-star Lauren (Love Boat) Tewes. Born Jennifer Leigh Morrow, she took her stage name (the Jason comes from family friend Robards) in 1976 "because I wanted a separate identity."

Yet between locations, Jennifer still lives at home, her room full of Art Deco furniture upholstered in coral-colored silk. She collects flapper dresses from the 1920s, and is nostalgic for a more glamorous past. "In the 1930s everybody was sensual, plump, without today's crazy preoccupation with thinness," she says. "Betty Grable's famous legs would not be on a poster today." Along those lines, Jennifer regained in just two weeks the 18 pounds she lost during Best Little Girl. Her favorite food is French toast with maple syrup and cherry jam. "And," she says, "I used to go to Häagen-Dazs and order three banana splits at a time!"