MARGARET ATWOOD's fourth novel tracks a love triangle over a period of two years, investigating and developing the connections between Nate, his wife Elizabeth and his lover Lesje. The imagery of the book is paleontological; most of the characters work in the Museum -- "whole chunks of time lie here, golden and frozen" -- and evolution, adaptation, survival, extinction, are on a personal level, the main themes. Lesje, the "other woman," works with and loves the dinosaurs. Although this is an extremely traditional modern novel, in that it is based on the free wheeling introspection of the main characters, their work-lives are an intrinsic part of the structure. Only Elizabeth, the wife, seems occasionally to spend an excessive amount of time lying on her bed, brooding.

But then, her rejected lover has just committed suicide. He could not adapt; he is extinct. Her semi-rejected husband, Nate, tries very hard indeed to adapt. When he starts his affair with Lesje, he is "handing himself over to her, mutely. Here I am. You may be able to do something with me." In relation to Nate, who half-leaves his wife, the author is a paleontologist of words, finding clues in their derivations. Nate "knew in advance . . . that separation is painful; he did not know it would also be literal. He had been separated; he is separate. Dismembered. He is no longer a member."

The evolutionary process that produced the personalities of Nate, Elizabeth and Lesje are charted in terms of mothers, aunts and grandmothers. There is an inevitability about their characters, as there is comically about the "Great Chain of Being" of Elizabeth's dreadful Auntie Muriel: "First comes God. Then comes Auntie Muriel and the Queen, with Auntie Muriel having a slight edge."

Lesje is uncomfortably multicultural and fluid, and a fantasizer. In the struggle for survival, Elizabeth is more than a match for her. People like Elizabeth can "blot you out," says Lesje. Elizabeth is powerful and a manipulator. Even her weaknesses are expressed in terms of power: "I feel as though energy is being constantly drained out of me, as though I'm leaking electricity." Elizabeth has "backbone," and money in the bank. The only thing that terrifies Elizabeth is losing her grip on what is happening: She must even control Nate and Lesje's affair.

The book has a subtly documentary air, like the best kind of women's journalism or the most sympathetic case notes. Events are precisely dated. Canadian social structure, domestic interiors, street habits are inconspicuously documented. Lesje and a friend walk "over to Yorkville and Cymberland to look in the store windows. It's no longer the place to shop . . . Queen Street West is the place now." Yet the writing is not pedestrian. The novelist is also a poet; one is reminded of this not by her lyricism but by her precision, as when Nate at a party stares down the meaningless clevage of a meaningless girl: "He watches this pinched landscape idly."

Life Before Man is a very skillful work, linguistically sensitive, not at all boring, utterly realized, disciplined, perceptive. It provokes a slight unease. Margaret Atwood is one member of contemporary women novalists adding to a body of fiction that in terms of technique, thoughtfulness, honesty and sheer intelligence has probably never been equaled. That sounds like a school-report; and there lies the unease.

Life Before Man is so responsible . There is in it no theme, no piece of characterization or narrative that could not be shown in an academic English department discussion to be functional, ordered, structurally sound, part of the overall conception. Lesje in the novel says to Elizabeth, "You wanted to supervise us. Like some kind of playground organizer." Margaret Atwood controls her characters in the same sort of way.

The great works of art are anarchic and have something irrational and inexplicable about them. "Organisms adapt to their environments. Of necessity, most of the time," though occasionally "with a certain whimsey," writes Margaret Atwood in this book, citing as an example the modified third claw of the hind foot of the Deinonychus dinosaur. Since the claw never touched the ground, paleontologists have speculated that its purpose was to disembowel prey. The dinosaur would have held an animal with his forefeet and balanced on one hind foot while using the third claw of the other foot to "slash open the stomach of the prey." It was a "balancing act, an eccentric way of coping with life," and it was "this eccentricity, this uniqueness, this acrobatic gaiety" that appealed to Lesje. Life Before Man is a good novel, but the author has both her feet on the ground. I suspect very good novels are written with the third claw. CAPTION: Picture, Margaret Atwood, Copyright (c) By M. Bedford