Street Theater : THE HEART OF THE WORLD, <i> By Nik Cohn (Alfred A. Knopf: $21; 371 pp.)</i>

Be warned. The metaphors and similes come gushing out of Nik Cohn like ketchup from a watered-down bottle. “It was a raw night, the damp so clinging that it seemed to leech at my flesh and suck, a vampire kiss.” This is a particular kind of writing, and you either love it or hate it, depending upon how much goop you like on your proseburgers. “Six feet two, the girl must have been, all legs and no breasts, and she was flexible as raw rubber.” Cohn slathers his pages with verbal condiments, tangy phrase-morsels demanding to be savored. “His hand was hairless, raw pink, the color of fresh bubblegum, with thick blue veins.”

Maybe all the descriptive imagery makes you feel you’ve stumbled into a B movie. But keep in mind, this is no Raymond Chandler fiction being served up here. The hard-boiled stories in “The Heart of the World” are true, the characters far too unbelievable not to be real. “Quirks,” the book’s Izzy Grove calls them. “Just people a little different, they got some kind of bug in their heads, some kinda notion.”

Cohn’s kinda notion is to take a long urban stroll. “This book,” he tells us, disingenuously, at its beginning, “is the partial record of a walk I made up Broadway, starting at the Battery and aiming for the Bronx.” Cohn’s is not to be a continuous saunter, but a perambulation that lasts for weeks, months, maybe years, with a rented room in a seedy hotel serving as the writer’s daily resting place. Perhaps he’s got decades to kill. Still, he never does make it much above Times Square.

But that’s a good thing, because the trip uptown is an author’s conceit for cramming his chapters full of personality profiles, historical anecdotes and private reminiscences. Some of the rambling is actually done by Cohn’s feet, much more of it by his pen. There are 8 million potential magazine articles in the Naked City, and Cohn seems to want to write all of them. And very nearly does.

First of all, he introduces us to Sasha Zim, a young Soviet-emigre-taxi-cab-driver (in New York City, that’s one word) and aspiring drummer. At the start of Part 1, Zim’s beloved instruments are residing in the bathtub of an acquaintance of Cohn’s. “Zim,” the young Russian says of himself, “he can be sleeping in taxi, in street, with woman, with woman in taxi, with woman in taxi in street, forgeddaboudit. But drums need get their rest.”

The mutual friend has suggested that Zim be the author’s “guide and minder.” Although it early becomes apparent to the rest of us that Cohn no more needs a tour director on the Great White Way than you or I do through our own living rooms, he does tend to wander, occasionally aimlessly. Zim, born to be a writer’s device, serves splendidly and colorfully as the pilot who frequently steers Cohn from one tale to another.

There’s the saga of Mr. Geraldo Cruz, known on the Street as Lush Life, “a girl so beautiful it hurt.” There are her friends Velma (a.k.a. Joe Wojcik) and Denise Denise (no middle name given); her sometime boyfriend, Tommy Blalock, he of the Dubble-Bubble hands; and the beefy transvestite who beat her up (“The only way she’d see forty again was on a NO SPEEDING sign”).

Meet Stoney Bissonette, a “Liberty Booster,” riding the ferry to and from the Statue, furtively engaged in the Pursuit of his own Happiness: the liberation of wallets from the pockets of sightseers. Check out Rashan Ray Perry who, after an unspeakable childhood, and despite the fact that he looks like a “ ‘Soul Train’ scarecrow, the advance man for a famine,” has survived to become a notable “warrior” of the Big Youth dance clubs. Spend some time feeding the pigeons with Ellen Fogarty, or selling Street News with Cleveland Blakemore, or barking like a dog with a girl called Wesley.

As he trundles along his broad way, Cohn pauses, now and then, to regale us with the well-known legends of New York history, fables of P. T. Barnum, Robert Moses, Harry K. Thaw. Digressions pile on divergences pile on tangents. Plots bump meaninglessly but harmlessly into one another like New Year’s Eve strangers on 42nd Street. There are always other blocks to walk, other pages to turn. By the middle of the book, the reader, like many of the Broadway denizens whom he encounters between these covers, feels himself being sucked deeper and deeper into the center of some teeming morass of humanity. Oddly enough, it’s a sensation that is not totally unpleasant.

Cohn, though, manages to stay above it all, shielding himself in occasional distancing Briticisms (words such as tiddler and bumf), and all those cute rhetorical tricks. The book is self-consciously organized into three sections (read: acts), separated by “Intervals” (oh, to be in England!), and a Coda for a finale. Broadway is, after all, a synonym for the theater, for the evanescence of drama, where one minute the stage bursts with life, and in the next minute the lights come on and the universe goes poof.

Ultimately, for the author, the “Heart of the World” is an organ pulsing with physical and moral decay, itself going poof right before the disbelieving eyes of its inhabitants. His Broadway is a decadent never-never land peopled by aged has-beens and naive never-will-be’s. “Before it became a garbage barge,” says Enid Gerlin, attorney-at-law, “this used to be a city.” Dick Falk, a theatrical flack, tells the history of Times Square: “It started out a stinkpot. Then it went downhill.”

In the end, there’s nothing more left for Cohn, or the reader, to see, or hear, or do. His characters are abandoned to write the last scenes of their scripts by themselves. In a tantalizing short note, coyly presented as the author’s date-stamp, we learn that Lush Life has died: “Shelter Island, December 9, 1990. In memory of Geraldo Cruz.” Only Cohn himself and Sasha Zim manage to escape at last from the Street’s malevolent magnetism.

New York-bashing is fun, but maybe Nik Cohn has skewed his sample just a little. There’s a list on the acknowledgments page of plenty of folks whose biographical snippets apparently didn’t make the tragic grade, and one wonders what the author might have written about Henny Youngman, for instance, or Rocky Graziano; about Gustav Schoeffer, taxidermist, or Bambi, pocket-sized Venus. And what about the famous names contrived to strew along our path, but whose stories he chose not to tell: Fiorello La Guardia, George M. Cohan, Diamond Jim Brady? We’ll have to wait for “Return to the Heart of the World” to find out.

In the meantime, please pass the relish.