For 15 years, computer engineer David S. Lifton has tracked the Kennedy assasination just the way he did "Project Apollo" during the moon landing.

He has always taunted other Warren Commission critics that he -- and only he -- would someday piece together the truth about Dallas with the meticulous throughness of a man whose background is math and physics and engineering.

Now he has completed an investigation that has obessed him since 1965 in a book, entitled "Best Evidence," that the prestigious publishing house of Macmillian is bringing out in January.

It apparently wasn't just publicity hype when Macmillan announced in a cover ad in the current issue of Publishers Weekly that "One hundred years from now . . . this book will still be shocking . . . because it tells, at last, the truth about the deception surrounding the killing of John F. Kennedy."

Phones have been ringing all over the United States among that network of prominent assassination aficionados who analyze obscure data about the events of Nov. 22, 1963, they way other people play bridge or chess.

Even Lifton's detractors are conceding grudgingly that he is onto "something important."

He has uncovered new evidence that he believes "if Lee Harvey Oswald were alive today, it would get him a new trial and he would be acquitted." He also makes a convincing case for an argument that President Kennedy's death was a "deliberate professional political murder -- and not a historic accident that was a quirk of fate -- planned by a group in government who wanted him removed from office."

It's about "faked evidence . . . disguises, camouflage . . . used to conceal the facts from all official government investigations."

It's about "the mechanics of a frameup . . . who orchestrated it and how the plan worked."

"Lee Harvey Oswald is innocent," Lifton argues, apparently more convincingly than anyone else has done before.

Lee Harvey Oswald, according to Lifton, was a "chance suspect," picked up because he had "bought a gun and had a fight with is wife and had made some threats against politicans."

He was a convenient scapegoat, Lifton says, "and it was easy to frame him in the eyes of the world. It's as if you had won a Nobel Prize by falsifying your lab notebooks on research and got away with it for years until somebody came along and checked your findings and said wait a minute, these notebooks are fake."

Because of libel laws, the book is a "how-dunnit instead of a whodunnit," Lifton says.

The military -- particularly at Bethesda Naval Hospital, where the JFK autopsy was performed -- are not going to like Lifton's startling new findings.

Sources familiar with Lifton's manuscript say he has uncovered "never before published documents that dispute those autopsy findings."

According to attorney Bernard V. Fernsterwald, head of the private Committee to Investigate Assassinations, the "deficiencies" of the autopsy affected "the whole investigation."

"A lot has already been said about the autopsy," Fensterwald said yesterday. "That it should have been done in Texas, that is should have been done by professionals. They were not professionals and there were a lot of high military officers standing around while it was being done."

Lifton, said Fensterwald, has tracked down and interviewed military witnesses never called by either the Warren Commission or the House select committee on assassinations."

"This isn't going to be light bedtime reading," he said.

Lifton, now 40, spent four years just rewriting his manuscript after it was accepted by Macmillan. Twenty other publishers, apparently not realizing the quality of his investigative skills, turned him down.

Living on savings and family money, he spent as much as $800 a month in long-distance phone tolls over a decade and a half in pursuit of his truth.

He made a lot of enemies along the way, one of his peers said yesterday, because he was forever tantalizing them with the claim that he was the only one on the right track.

"He always claimed he was the one researcher among us who knew the answer," one source said yesterday. "We would say, 'All right, why don't you tell us then, why wait?' There is bound to be a lot of flack about why he didn't make his findings known before the House select committee on assassinations hearings."

Lifton's critics accuse him of being "secretive" and "paranoid" about his work. But he dying to talk about it now. His publisher has had to muzzle him with threats to keep him from giving away all the tantalizing little details before the publication date.