There's more to Brooklyn than a bridge and Barbra Streisand. On this Sunday afternoon a reporter and photographer have ventured into a tree-lined brownstone neighborhood to visit the four-story walk-up of Kelly McGillis—a struggling actress who became a movie star last week with the release of Witness, a suspense-love story from Australian director Peter (The Year of Living Dangerously) Weir. McGillis, 27, has won the hearts of the critics with her tender portrayal of Rachel, a young Amish widow whose small son is the only witness to a grisly murder. The film stars Harrison Ford, Mr. Indiana Jones himself, as an undercover cop who hides out in Rachel's farmhouse and stays to fall in love.

The actress, whose only other feature film was 1983's Reuben, Reuben with Tom Conti, looks nothing like Rachel, shockingly unlike her in fact. Rachel is pudgy, has brown hair and wears long drab dresses and capes. McGillis, in a light gray jumpsuit, is thin and blond, with soft gray eyes and a nervous, robust laugh. Also unlike Rachel, she's anything but naive to the ways of the modern world. "I've never, never in my life been cast as anyone innocent until this movie," she says. "I've played various strong women or whores." Although reared in Newport Beach, Calif., she has become a blooded New Yorker: "Yeah, I've been mugged three or four times. Look, when you're tall (5'10") and blond and ride the subway, you get picked on."

Now that she's finally made some real money, McGillis can finally afford to rent a place of her own. No roommates this time, just her two enormous cats, Spike and Ezra. "My boyfriend Chuck hates cats," she says, "and you can print that." Chuck Primeau, who's 34, moved from San Francisco, where he was selling insurance, to New York, where he is now a social worker. "We lived together for a few months, but it didn't work out," she says. Marriage, for now, is also out. "No, no, no, no, no," she says. "My career is the most important thing." Since she was 17, McGillis has been supporting herself on and off by waiting tables. "People tend to treat people who wait on them as if they didn't have a brain in their heads," she says. "I had one woman whistle at me in a restaurant to get my attention. I said, 'Don't, I'm not a dog.' "

She is also not a health fanatic. While she talks she chain-smokes Merits, and her eating habits defy all that the best minds of her business—Linda Evans, Victoria Principal, et al—have passed on about the secrets of beauty. Finishing off a lunch of canned minestrone and Diet Coke, Kelly is radiant. Why has she never thought about modeling? "I'm not good-looking enough," she says, with what seems like honest humility. "When I was young I was too heavy [190 pounds]. My self-image is based on how I looked then. In high school no one ever asked me out on dates. I did go to the senior prom, but I don't want to talk about that. I don't want to insult the poor person who took me."

When McGillis screen-tested for the role of Rachel, she had a valid reason for not feeling gorgeous. "I had a cold sore on my face," she recalls. "Peter [Weir] said, 'It's okay, honey, everybody gets 'em.' I said, 'Yeah, but not everybody's being seen by all of Paramount Pictures.' So I acted with my hand over my mouth." Says Weir: "She had a glow that was apparent, even in the screen test. Film is faces, and you could look at that face for a long time."

Before shooting began, McGillis went to the farm country near Lancaster County, Pa. to study the Amish, the Mennonite sect that holds services in German and has retained 18th-century values and life-styles. "I couldn't find any tapes of their dialect, so I took a recorder and taped them subversively," she says. "I met a lot of Amish people and got to live with an Amish widow named Mary, the mother of seven. I stayed on her farm for three days and learned to milk cows. I got up at 4 each morning, which is when I'm used to going to bed. I planted seven rows of potatoes by hand. Mary laughed 'cause I couldn't get my rows straight." Amish doctrine requires separation from the world and worldly things. The guarded Amish refused to serve as extras in Witness. "I left Mary's farm 'cause they had printed my picture on the front page of the local paper, and I didn't want to get her in trouble," says Kelly.

Witness is, among other things, a love story, and while there is no overt sex, McGillis does have a topless scene. "I thought my folks would say, 'Buy a bra,' when they saw the film," she says. "I have a problem about people seeing me in, you know, the buff. I think, sure, they've seen me, but I haven't seen them."

A doctor's daughter (Mom is a housewife), Kelly grew up with three younger sisters in a house on the ocean. Surfing and cheerleading were for other California girls. Kelly wrote, directed and starred in her own plays in front of her grandma's fireplace and forced her sisters into supporting roles. "I was a one-woman show," she says. She studied drama at the Pacific Conservatory of the Performing Arts in Santa Maria and in 1979 moved on to the acting program at Manhattan's Juilliard School, graduating in 1983. Forget the soaps and TV movies she did before Witness. Kelly has. "They'll ruin my career."

Writer-director Garson Kanin has cast her opposite Christopher Plummer in his play Peccadillo, which premieres in Palm Beach, Fla. on Feb. 26 with hopes for Broadway in April. And if the play doesn't lead to other offers, will McGillis have to resume waitressing? "Oh," she says, in a soft voice, practically melting, "let's hope not. This is such a tenuous business." Relax, Kelly. After Witness you can hang up that hairnet for good.