Grace Under Pressure : GRACE, <i> By Robert Lacey (G.P. Putnam’s Sons: $24.95; 463 pp.)</i>

The story of her life, as Robert Lacey so convincingly tells it, is of Grace under pressure. Pressure that began in childhood and never really let up. Her father, Jack Kelly, came from a poor Irish-American family in Philadelphia, but by the time Grace was born in 1929 he made his first $1 million in the construction business and built a 17-room mansion in the fashionable hillside suburb of East Falls. Like Joseph Kennedy, he was a philanderer who preached family values and a formidable patriarch who brought up his children to become all-American winners. Although he judged Grace the least likely to succeed, she turned out to be the only real achiever. The reason, according to her brother, was that “she got away from home early.”

But it seems she never really got away. When Jack Kelly reluctantly agreed to let Grace enter the American Academy of Dramatic Arts in New York, he was openly skeptical of her future as an actress. The pressure was on to prove him wrong, which she set out to do with a mixture of ambition and wounded self-confidence. It was the first of several tensions in Grace’s life that she never resolved, for Kelly could never bring himself to admit he’d underestimated his daughter. “I’m glad she’s making a living,” was the nearest he came to a public compliment.

A shy and plump adolescent who spoke with an unattractive nasal twang, Grace had lost weight and acquired a striking angelic beauty by the time she arrived in New York at the age of 18. At the Academy she also acquired a new voice: smooth, sweet and high society. But the innocent-looking blonde from a Catholic home, a firm believer after nine years at convent school, was secretly coming to terms with a high-powered sexual drive. If confession could ease a guilty soul, she still had to keep up a front. Jack Kelly had his affairs on the side but Grace was a girl and supposed to be “good.” She fabricated a cool, refined image so successfully that more than one early lover was astonished at the way she dropped all pretense in the bedroom.

By then Grace was involved in her second intense affair with a married man, setting the pattern for most of her later romances. Among the men she fell in love with after she became a star were Clark Gable, Ray Milland, William Holden, Oleg Cassini, all married or divorced and totally unacceptable to Catholic parents. When they found out, as they always did, Kelly hit the roof; and as Lacey writes, “when it came to the ultimate loyalties, she was her father’s daughter.” But each time the rebel yielded to the conformist, she acknowledged an ongoing conflict within herself. Jack Kelly had taught his children that winners must always behave like winners, and this was another order Grace obeyed. The loser in many emotional battles always hid her pain and kept smiling.

Denial, apart from the personal cost, was the worst possible training for an actress, and Grace’s movie career got off to an unpromising start. Although white gloves made the right impression on Fred Zinneman when he cast her as Gary Cooper’s prim Quaker wife in “High Noon,” she gave a flat performance in a flat role.

In the meantime, Hitchcock viewed an unsuccessful test that Grace had made for another movie. Detecting a “snow-covered volcano,” his imagination was stirred. The perfect lady who in Hitchcock’s words could be “quite astonishing when she got going,” was a recurrent erotic fantasy in his movies. And Hitchcock’s fantasy, of course, was Grace’s reality. The result was a partnership in which director and actress pressed each other’s private buttons.

It’s impossible to guess how her career might have developed, for she was never as vibrant and original again, and worked only with run-of-the-mill directors in the two years that remained of her life as an actress. At the age of 26 Grace found her Prince Charming.

It seems more than coincidence that Prince Rainier of Monaco was the first man in Grace’s life of whom her father (and equally strict mother) approved. Although Jack Kelly had always shrugged off her success as a movie star, he gave Grace his full blessing in the role of Her Serene Highness. “This,” he said, “is going to be a big thing.” Lacey believes that the couple fell genuinely in love. At least they genuinely believed they did, although Grace had no idea what she was getting into.

In her new life, Grace soon found herself under familiar pressure. On the surface, a devoted wife and mother of three children; beneath it, an increasingly lonely woman whose marriage had settled into a sometimes rocky friendship. Obsessed with developing the real estate possibilities of Monaco, Rainier allowed tax exiles and business corporations to turn the place into a concrete jungle of hotels and high-rises. Although Grace never betrayed her feelings about this, her public activities suggested them. She founded a ballet school and garden club, began to give poetry readings at European arts festivals. But the conflict between rebel and conformist continued.

She enjoyed her royal image and at the same time felt trapped by it. Motherhood, then eating and drinking a bit too much, made her put on weight. She found release in a couple of extramarital affairs with men considerably younger than herself, she kept smiling, but her life ended as it began, in a home where she never felt completely at home.

This is a definitive biography with a shrewd final verdict on its subject: “A beautiful illusion created for an age that liked to be deceived.” Forty years later, of course, in an age that likes to be undeceived, the media would have so thoroughly exposed Grace’s private life as a movie star that Rainier would never have married her. And the final irony is that Grace died after an accident in which she lost control of her car. This passionately driven woman had always been a bad driver.