When a book is under attack, it's easy to slide from "controversial" (which is usually good) to "tainted" (which is always bad).

"Sleepers" -- which has been promoted by its publisher as a "true story" and derided by its critics as dubious if not deceitful -- is wavering on that edge.

In the wake of several negative stories, Ballantine Books decided yesterday to refuse all requests for newspaper or magazine interviews with the book's author, Lorenzo Carcaterra. Television and radio, however, remain okay.

"We've been burned repeatedly and we think unfairly," said Peter Gethers, the book's editor. Carcaterra's comments "have been taken out of context and abbreviated by the print media, with a slant that has been wrong and mean-spirited."

The book says in its prologue that the author has "changed all the names and altered most of the dates in order to protect the identities of those involved." But Gethers says he has proof that the story happened as it's told.

"Sleepers," which was published last week and is already on national bestseller lists, tells the story of how in 1967 the author and three of his friends played a prank that went wrong, resulting in grave injury to an elderly man. Sent to reform school in Upstate New York, the youths are assaulted, abused and raped by the guards.

Twelve years later, two of the boys have become thugs. In a bar, they chance upon one of the sadistic guards and immediately shoot him. One of the original quartet of friends, now an assistant district attorney, gets himself assigned as prosecutor for the murder. He conspires to lose the case and let his buddies go free. It's a story about friendship and revenge told in a style that, as the first advance review in Publishers Weekly put it, "reads like a novel."

Too much like one, according to some of the commentary. "Is new book fact or fiction?" wondered the New York Daily News. "The reader can't help but be suspicious of its authenticity," asserted Entertainment Weekly. "There is growing talk in book publishing that the story is at least in part fiction," said the New York Times.

Latest and most damaging is an article in this week's Time magazine. "Not since Joe McGinniss began dreaming up things that Senator Edward M. Kennedy might have thought, in The Last Brother' (1993), has there been such an elastic and accommodating definition of nonfiction as Carcaterra's," the magazine wrote.

Responded Gethers: "We think {the coverage has} been irresponsible, as well as nasty. The New York Times has been really irresponsible. {The Times reporter} ignored sources we gave him, ignored information we told him we would make available. Time magazine was gratuitously nasty."

Some of the campaign against the book has been whipped up anonymously. A poorly punctuated letter sent to a reporter at The Washington Post last Friday claimed "Sleepers" was "a hoax that keeps getting bigger and bigger. The author and publisher insist on selling it as a true nonfiction story even though they know better. I challenge you or anyone else to find one fact that can be independently verified . . . Its disgusting and not only is it a hoax its a cynical hoax. Raped indeed."

The letter was postmarked New York City. The address, typed on another sheet of paper, was stuck to the envelope with tape. At one point, the sender got his dirty finger caught up in the tape, which means there is part of a perfect fingerprint on the envelope. The Unabomber never makes mistakes like this.

Gethers said Carcaterra "has no idea" who could have sent the letter. "My conjecture is that this all stems from the fact that Lorenzo sold the book to the movies for over $2 million. There's an enormous amount of jealousy and bitterness over that." Robert De Niro and Brad Pitt are reportedly slated to star in the film version of "Sleepers." The title is slang for a juvenile sentenced to serve longer than nine months.

Curiously, Gethers referred to Carcaterra as "one of the good guys." That's also the name the sender of the letter is using: "The Good Guys." Told this, Gethers was emphatic that Carcaterra is not sending out the letters himself.

Carcaterra, a former Daily News reporter who has written a previous autobiographical book, will continue to do television and radio interviews, Gethers said. "He feels he can make his case honestly there." The publisher turned down a number of print interview requests in the wake of the Time story.

A key point being disputed in the book is when Michael, the member of the quartet who has been working in the Manhattan district attorney's office for only six months, gets the case assigned to him. The D.A.'s office has said in interviews that a neophyte prosecutor would never handle a homicide.

Carcaterra responded to Time that the real-life Michael was not necessarily a six-month assistant district attorney the way he was described and maybe was not even working in Manhattan. "The what, where and when these things happened were not as important to me as the fact that they did happen," he said.

That sounds like trying to have things both ways -- the urgency of reality plus the freedom of fiction. So far, readers seem to be responding. But the writer's credibility has taken a hit. CAPTION: Lorenzo Carcaterra stopped giving print interviews after some publications said his book may be more fiction than fact.