AN ADULTERY By Alexander Theroux Simon and Schuster. 396 pp. $18.95

ADULTERY WAS once the ideal subject for the novelist. Anarchic passions crushed against inflexible societal mores; the awful daring of a moment's surrender led inexorably to the draught of poison or the wheels of the oncoming train. But that was long ago, before prime-time. In a contemporary novel like Couples, marital deception is no more shocking than the idea of sleeping without pajamas.

Don't imagine, though, that Alexander Theroux's new novel, An Adultery, in any way heralds a revival of strictures. The book is, it's true, about an adulterous affair. But society could not care less. Indeed, society -- that is to say other people -- scarcely intrudes upon these pages. An Adultery, like Bergman's film Scenes From a Marriage, focuses relentlessly, exhaustively, and at times exhaustingly, on the ebb and flow of passion between two driven lovers.

Painter Christian Ford first spots Farol Colorado at a gallery in St. Ives, N.H. "She was a tall striking woman about thirty or so who worked with her head down as if she'd have to work that way, framing, until the day she died." He is instantly captivated and almost as quickly involved. The fact that Farol is married is neither an obstacle, nor, for the reader, a source of tension; the husband is never brought onto the stage.

An Adultery mimes the intense absorption that passion brings. As the lover, Christian, can think of nothing else, neither can the prose. Theroux marks and ponders every heartbeat, taking us from the first hours of lovemaking ("She had eyelash kisses, cowpecks, pushsoft kisses, lizard kisses, bitesucks, flicks . . . ") to the desolate weeks, several years later, when Christian finally understands what kind of person he's been in love with.

If we define plot as external action, then there's precious little plot in this novel. Theroux's mode is to isolate significant chunks of time, to annotate the telltale events and exchanges, and then to speculate at length on their myriad implications. The speculations are, in places, riveting. The author has mined the heart for its paradoxes and a-logical twists: "She felt a certain power, a justice, I think, in hurting the man whom she felt so often had hurt her. But it was her hurting him that ironically made me mistrust her."

But there is finally too much of Christian's musing. After four or five or 10 pages of his cogitating -- much of it dense and abstract -- the reader longs for some of the cheap thrills of action. This is where our regret for the lost taboo comes in -- where everything is permitted, meaningful dramatic situations are hard to come by.

STILL, within the close confines of his narrative, Theroux has created a memorable, often compelling, portrait of an ill-starred love. And he has done so with uncompromising thoroughness. Though much of the prose was written with the head, the originating impulse was clearly in the gut. The book is an exorcism; the author is driven by the need to tell, but also by the need to understand.

How else are we to explain the fixating recurrence of Farol Colorado? The woman is not just presented to us -- she is inflicted. We get her from every imaginable angle, page after page. Until she becomes to us everything that she was for Christian -- quick, coy, delightful; vapid, selfish, grasping. The cycle repeats. Christian glimpses her deeper nature, her pathological predatoriness, early on, but he is powerless against her urgency and charm. He forgets what he knows; we forget. Then it's too late: Farol twists the knife again.

Not since Henry Miller's epics of betrayal have we had so grim a vision of the destructive power of love.

Sven Birkerts is the author of "An Artificial Wilderness: Essays on Twentieth Century Literature."