SAVAGE GRACE. By Natalie Robins and Steven M. L. Aronson. Morrow. 492 pp. $17.95.

UNDERNEATH EVERY soap opera there is another, more potent one wanting out. In Savage Grace, authors Natalie Robins and Steven M. L. Aronson present the Baekeland scandal of a few years back -- plastics heir kills mother. With brutal clarity and in horrifying detail they subvert and revitalize what has been labeled "soap opera," mating the classic (the serial aspects and the emotional sweep of the form) with the trendy-trashy. It's a chilling wedding of a Mommy Dearest with Long Day's Journey Into Night.

With high praise from Norman Mailer, William F. Buckley Jr. and E.L. Doctorow adorning the book jacket, Savage Grace lives up to its advance notices. It tells the story about the great-grandson of the inventor of plastics, who was brought up to be brilliant, was encouraged by Robert Graves and James Jones to pursue a career in painting and poetry, had homosexual affairs, slept with his mother, killed his mother with a kitchen knife, spent time in a psychiatric hospital, was released in a bureaucratic foul-up, stabbed his 88-year-old grandmother eight times, and, finally took his own life, smothering himself with a bag over his head -- a plastic bag.

There is something quite grandiose, operatic, and, of course, finally banal in this resolution. Authors Robins and Aronson have chosen to present the story in documentary fashion, as an Edie-like oral history. The format is essentially like a relay race in which dozens offer pieces of story before handing the baton to the next runner. Letters, psychiatric reports, interviews only add to the sense of sustained morbidity and doom. And at the end of the book there is a roll-call reference of the participants -- a biographical glossary of all the little foxes.

In this way, the reader sifts through the often contradictory material in the same manner as a juror hears evidence at a trial. Who or what is to blame in this tragedy? Or was it a mere folly, collapsing into greed, the pursuit of social distinction and power? Tony Baekeland by all reports was an enchanting child. William Styron described him as an "absolute young Adonis." Tony's mother, Barbara Baekeland, was another beauty with a shock of violent red hair and a propensity for hedonism and masochism. Tony's father, Brooks Baekeland, was an adventurer whose family money bankrolled Brooks' expeditions to Peru to search for lost Incan cities and kept his family in glamorous splendor in New York, London, Paris, and various other vacation digs.

Tony had it all, and more. As a child, he was required by his doting father to read aloud to cure his stuttering problem. (Brooks's choice of reading material was the Marquis de Sade!). Brooks spoke with pride to an acquaintance that his young son had the imagination to tear off the wings of flies to experiment with the theory of "equilibrium." Francine du Plessix Gray remembers staying with the Baekelands in France, where a teen-age Tony methodically stole jars of baby food intended for du Plessix Gray's infant. ("He wanted to be a baby. He'd never been a baby.")

WHEN IT WAS learned that Tony was enjoying homosexual encounters, his father began refering to Tony as "her son," while Barbara, taking a gamut of drugs along with Tony, seduced her son supposedly to "cure" him of his homosexuality. (When informed of the affair, a friend commented drily, "Sons and lovers -- nobody knows the difference anymore.") Meanwhile, as Tony's paintings became more and more bizarre (pictures of his mother decapitated, etc.) and his behavior violent (especially after Brooks ran off with Tony's "girlfriend" Sylvia), Brooks refused to pay for Tony's psychiatric care, dismissing the mental health field as "professionally amoral."

Brooks threatens to become the heavy of the book, continually hanging himself with such arrogant reveries as, "I was always free. I was always successful in everything I wished to do. But I despised success. I despised money and show. I laughed -- a grave offense to those who cannot laugh! I thumbed my nose at my father and at the sheepism of Man." But then, in a series of long monologues, Brooks remembers his inventor grandfather with such compelling frankness and poignance that it humanizes Brooks. And, here, the book's circular theme and format again comes into focus: the penniless immigrant who left a dying Europe with the American dream gave birth to decadent royalty who finally self-destructed with an incident in a London penthouse.

Savage Grace puts the sting back into family violence. It does this not with "clean" emotions; the familial details are too messy and cruelly witty -- they cut to the bone. After killing his mother, Tony calmly picked up the phone and ordered Chinese carry-out. When Brooks was informed of his wife's death, he turned to his girlfriend and said, "She's again found a way to get at me." When a psychiatrist told Barbara Baekeland less than three weeks before her death that her son might kill her, she replied, "He's been murdering me since he was born." She said several times that she fully expected him to kill her and apparently offered no resistance in this particular attack -- as if the act finally completed her.

And Tony, poor Tony, the perpetual victim and the cause celebre of the social set, never showed an ounce of remorse. Even though, his father reminded him, "You didn't hit your mother with a banana, you hit her with a knife!" Savage Grace is archetypal yet original -- a classic story of mummy and murder.