BOOK REVIEW / FICTION : The Possibilities Within Each Life : SWANNY’S WAYS by Steve Katz; Sun & Moon Press $22.95, 554 pages

The key here is not to be intimidated, especially by the title. “Swanny’s Ways” isn’t “Swann’s Way,” for all its narrative trickery and its Proustian emphasis on memory and obsessive love. In fact, the conclusion of the Steve Katz trilogy that began with “Weir & Pouce” and “Florry of Washington Heights” is about as user-friendly as a long, postmodernist novel can be.

It’s a lot easier to read than to describe. Think of a summertime river whose channels braid among islands and sandbars--a maze of alternate ways for the water to go, but still, in the end, one river.

Jackson Ryan, a purveyor of insects to collectors and industry, formerly chief of the Fanwoods gang in the Washington Heights section of New York City, meets down-and-out William (Swanny) Swanson, a perennial night-school law student, formerly a member of the weaker Bullets gang--”nice boys, with mothers and fathers”--at a lunch counter in 1990 and offers to help him.

Swanson begins sending Ryan manuscripts--sexy, funny, violent, nostalgic tales about how, in the 1960s, he became fixated on the earlier murder of 15-year-old Florry O’Neill, a girl both men had loved in high school. Ryan adds his own comments, pointing out the inconsistencies and implausibilities of the stories (in one, Swanson himself is shot dead), yet fascinated by the author, who “doesn’t know what he is doing, and yet proceeds.”

A feeble-minded junkyard worker, Sledge, has spent years in prison for Florry’s murder. But Swanson claims that the real killer was his sadistic former gym teacher, Phil Kutzer. After years of repressing this knowledge, he says, he woke up to the need to atone for his cowardice, find Kutzer, free Sledge and do right by Florry.

Swanson--half Jewish, half Irish--visits South Carolina for his father’s funeral and meets a half-sister he never knew existed. He sees--or thinks he sees--Kutzer as a guru at an Upstate New York commune and as a Mafia hit man in Little Italy. He visits the prison where Sledge, now a Black Muslim, is incarcerated. He has almost interchangeable girlfriends of various races, who all leave him when they realize the depth of his obsession.

The stories work so well on a realistic level that we are slow, even reluctant, to admit that “Swanny’s Ways” isn’t a realistic novel. One clue is how quickly and comically Ryan’s hyperrational facade dissolves. Another is the way Katz, like Philip Roth in “The Counterlife,” repeats passages to mark clearly where the narrative channel splits.

As story follows story, we wonder why the genuine intimacy Swanson seems to enjoy with his girlfriends always evaporates so soon. We notice a pattern of sexual transgression and guilt. Swanson makes love to his half-sister. He fondles a girl tied to the wall of the guru’s bedroom and another girl flipped out on LSD in Central Park. He picks up the Iranian lover of one of Sledge’s fellow convicts.

In mid-novel, a fantastic, allegorical section called “Red Shift: Dream Time” leaves realism behind altogether and prepares us for the more crooked meanderings to come.

Swanny, after all, has more ways than one. We often say that a person is a bundle of conflicting personalities. Katz is saying that a person is also a bundle of possibilities, some realized, some not.

The portrait we are given here is blurred and enriched by the things Swanson (and, for that matter, Ryan, Florry, Kutzer and others) did, almost did, could have done, might have been if the shuffle of alternate universes had turned up a slightly different card.

Suppose Swanson himself killed Florry? We get that story. Suppose Florry didn’t die and Swanson married her and they had three kids? We get that story too. Suppose Ryan’s wife came out as a lesbian and Ryan became a psychiatrist as hard-fisted as the street tough he used to be? Suppose Swanson became a homeless man, or a sleek lawyer at last, or found a dying homeless man in an alley with his own name, William (Swanny) Swanson? We get all those.

The result? A portrait that coheres emotionally, though its facts are all in doubt. The river is still one river, Swanny still Swanny. This book is also, despite its growing sadness, a love song to Katz’s vital, decaying native city and a surprisingly complete picture of America, its mid-century idealism fading as it slouches and wisecracks toward the millennium.