Author Barbara Goldsmith spent five years researching someone else's bitter family feud. She is not anxious to have one of her own, and her husband, film director Frank Perry, agrees. At issue is her just-published book on the 1934 custody battle over Gloria Vanderbilt, then a 10-year-old American princess.

"Who wouldn't want to direct the movie of Little Gloria, Happy at Last?" he says. "I'm panting to do it. But not if it will damage the relationship with Barbara."

Goldsmith is wary of creating conflict too. She says she would like to write the screenplay, "but I would have trepidation doing one with Frank. I never wanted people to say: 'Barbara's riding his talent.' " It's a particularly sensitive area since Frank's first wife, Eleanor, was a scriptwriter who teamed up with him on such successful films as David and Lisa and Diary of a Mad Housewife. They were divorced in 1971 on grounds of incompatibility.

Little Gloria was published this week by Alfred Knopf with paperback rights already sold for $672,000. A million-dollar film deal is in the works—no director specified. The book meticulously reconstructs the trial in which Gertrude Whitney, a blue-blooded patron of the arts, tried to prove that her sister-in-law, Gloria Morgan Vanderbilt, was an unfit mother. Gertrude won the case (the elder Gloria was accused of being a lesbian) and custody of the child. In her research, Goldsmith traveled to seven countries, interviewed 202 people at least three times, talked to another 97 once and hired a researcher to question 55 more. Gloria Vanderbilt, now 55, refused to talk herself. "She said it would be too painful," says Barbara.

While Goldsmith explored the Vanderbilts, Perry was moving gingerly into TV land. After his last feature film, Rancho Deluxe in 1976, got medium-cool reviews, he directed the pilot for the NBC series Skag, starring Karl Malden, and the 1980 Peabody Award-winning TV movie Dummy, with LeVar Burton. Now Perry is returning to films. In September he will direct a feature from his own screenplay based on Irwin Shaw's best-seller Nightwork. "It's popcorn, a fun divertissement," Frank says. "No heavy statements."

The remark characterizes his approach to life these days. "I used to have a ponderousness, emotional and physical," he says. At one point the 5'11" Perry was up to 250 pounds: "I was an actuarial disaster." "Frank used to take up a lot of room at parties," jokes friend George Plimpton. Perry admits: "I liked to eat, drink and smoke a lot. Everything I could do orally, I did. I suppose it was to beat up on myself." He was afflicted with a nagging fatalism. "I had always felt I would die by the time I was 35," he recalls. "Why have a backhand if you're not going to play tomorrow? Why buy a carton of cigarettes if you won't be around to smoke them?" (He bought a pack at a time.)

Enter Barbara. She and Frank (who are both 49) had crossed paths at parties before. In 1971 he was separated from Eleanor; Barbara and C. Gerald Goldsmith, an investment banker, had split too. Hearing that Barbara was available, Frank invited her to dinner. "She was so smart," he says. "She talked about people, books, movies. I was knocked out. From that point on, there was never another woman."

For Barbara, things were less intense. "Frank sort of sneaked up on me," she says. "He seemed so old at first. I remember him bawling me out for refilling my own wine glass in some fancy restaurant." With her encouragement, Frank took up tennis and, sipping diet cola and chewing sugarless gum all day, lost 60 pounds in eight months. His mood lightened too. "The demons were exorcised," says Perry. "It wasn't 'Poof! A remake!' It took a lot of hard work. But Barbara gave me a reason to do it. She younged me up."

Perry moved into Goldsmith's 10-room Park Avenue duplex in 1974. They were married two years later. He dotes on Barbara's three children: Andrew, 23, John, 18, and Alice, 20, who, Goldsmith recalls, "was terrible to Frank, mean at first, whiny and sarcastic." She was quickly won over.

Perry's own childhood was not happy. His father, a New Jersey stockbroker, and his mother, a niece of steel magnate Charles Schwab, were divorced when Frank was 13. "My mother was an alcoholic, then an obsessed member of AA," he recalls. "She turned our house into a drying-out center." Frank overate and developed a stutter that still flares up under stress.

At 15 he was parking cars at the Westport County Playhouse in Connecticut and drinking beer with Thornton Wilder, who was acting in his own drama, Our Town. Enamored of the theater, he quit the University of Miami after three and a half years to found a playhouse in the Bahamas. Later Perry became a Broadway stage manager and an associate producer at New York's Theater Guild. In 1959 the Guild produced Third Best Sport, co-authored by a Cleveland writer named Eleanor Bayer. She and Frank soon married; Eleanor was 16 years older.

After they divorced, Eleanor wrote a novel, published in 1979 as Blue Pages, about a woman filmwriter whose younger husband, a director, leaves her for someone else and then loses a lot of weight. She still insists it's not about her and Frank. He says, "I find it hard to reconcile Eleanor's feminism with my paying her $26,000 a year alimony." Barbara says, "Everyone in Blue Pages betrayed her. She's an injustice collector."

Barbara Lubin was one of two daughters of a Manhattan accounting and real estate executive and a woman who once taught drawing at Barnard College. "My father disapproved of private schools on the grounds that they turned out snobs," she remembers. "I went to public school and contracted lice."

After graduating from Wellesley, Goldsmith became entertainment editor of Woman's Home Companion in 1954. A week later she was interviewing Clark Gable. She remembers, "He said he'd give me one hour. I said: 'Oh no, Mr. Gable, I'll lose my job.' " She spent 10 days with him. That same year Barbara married Goldsmith.

After her children got past the toddler stage, she returned to writing, notably for the New York Herald Tribune and New York magazine. Her profile of Warhol starlet Viva in New York was a reputation-maker. "She told me she felt if you're not with a fellow you like, you're better off masturbating," Barbara recalls. "We printed it and got hundreds of outraged letters." When she became senior editor at Harper's Bazaar in 1972, she says, "I tried to get in stories by Tennessee Williams instead of how to care for your feet." In 1975, while researching The Straw Man, a novel about the New York art world, she chanced upon legal documents that piqued her interest in the Vanderbilt case.

She is now contemplating a book about women archeologists; Frank has another film in the works—The Front Runner, based on a 1974 novel about a gay track coach. They can be each other's severest critic. When they were dating in 1971, Perry showed her a rough cut of his film Doc, with Stacy Keach and Faye Dunaway, and asked what she thought. "I think you're in a lot of trouble," Barbara said; the critics later agreed. Frank in turn read Little Gloria in manuscript and suggested a number of revisions, some of which she made.

When the couple tries to relax ("Obsessives don't have hobbies," jokes Goldsmith), it is with friends like Roy Lichtenstein, Larry Rivers, Paula Prentiss, Dick Benjamin, Joan Didion and John Gregory Dunne. Frank often whips up pasta or chili at their weekend home in East Hampton, that Perrier of Long Island watering holes.

"It's wonderful to see two strong talents who don't have the slightest ego collision," says another friend, author Tom Wolfe. "They are more philosophical than most ambitious people." Not just philosophical—amazingly romantic. "He sends flowers just because it's Monday," sighs Goldsmith. Frank asks, "Why does the lamb love Mary so?" then answers, "Because Mary loves the lamb."