THERE HAVE BEEN many biographies of many Kennedys. Undoubtedly there will be many more. The virtue of this one -- Jack, by Herbert S. tParmet -- is that it reduces at least one Kennedy to human scale. No hagiography here, nor any polemics; no lofty prose, wistful eulogies or devastating indictments. Devotees of Arthur Schlesinger and Victor Lasky will be equally disappointed. Yet after two decades of Kennedy-inspired passion -- a mixed blessing for country, Kennedys and biographers alike -- dispassion provides more than a respite. It's also surprisingly effective as a cathartic.

Jack covers, in minute detail, Kennedy's life before 1960; a second volume (planned for 1982) will deal with the presidential years. The scale of Parmet's work reflects his painstaking approch: he reconstructs JFK's youth and early career much as a detective might reconstruct a homicide. The facts come first. They also come second and third. They must be collected laboriously, winnowed and sifted, then arranged chronologically to yield up their truth. It is a method of plain hard work, permitting no flights of fancy, no premature conclusions or great leaps of imagination. Parmet has come to chronicle Kennedy, not to judge him.

What emerges from this mass of detail is not "news," but a different perspective; a rather remarkable portrait of one man's personal evolution. Kennedy's contemporaries may already sense that change and growth marked his brief public life. Younger generations, however, are apt to associate metamorphosis only with his brother Robert, imagining Jack to have sprung, like Athena, somewhat unruly but nonetheless full-blown from his father's head. The facts, as Parmet recounts them, suggest a far more complex and painful ontogeny.

Jack traces Kennedy's early years through three relatively distinct stages. As a privileged but often sickly adolescent, he appears to have been an undirected, albeit spirited, underachiever. As a young man, after the war and the death of his brother Joe, he seems to have been directed largely by his father, his own docility reflecting in part the distraction of quite grave illnesses. Only as a senator -- and not immediately even then -- did Kenney apparaently become more independent, more sophisticated and captivating, aided not only by a brainy staff and particularly enlightening foreign travels, but also by moden medicine's advances. By then, of course, his past held many hostages -- mistakes, manipulations, indiscretions, false starts, secrets.

That Parment parades so many of these hostages through a single book will probably irritate Kennedy partisans. Regrettably, Parmet's publisher doesn't help matters. "Could J. Edgar Hoover really have doomed JFK's ellection?" asks a publicity flyer. "Was Jack Kennedy's reputation as a womanizer valid? Did Joe Kennedy 'buy' the Boston Post for Jack's 1952 campaign? What was JFK's relationship with Richard Nixon?" (The apparent answers: "probably," "evidently," perhaps," and "complex.") Disembodied and out of context such "revelations" would be mostly stale; old news. Parmet's achievement is not to catalogue them but to provide the missing context, indicating how each shaped Kennedy and his career.

Anticommunism and McCarthyism, for example, bedeviled Kennedy in Congress, As a House freshman, barely 30, he out-Nixoned Nixon ("it was Congressman Kennedy and not Senator Nixon who got the first citation of a Communist for perjur," Adlai Stevenson reminded Bay State voters in 1952, at Sarent Shriver's request). Only a parliamentary twist of fate prevented Kennedy from stressing his past support of McCarthy while simultaneously voting to censure him only for the excesses of his staff. Kennedy's later change of attitude would be scorned as expediency, the calculated act of a presidential candidate more concerned with liberal opinion than with the continued molification of East Boston's Irish Catholics.

Parmet does detail the political considerations for Kennedy's shift, as well as the personal ones (McCarthy and Kennedy shared an odd friendship), but he adds another point: belatedly, Kennedy realized he hadn't known what he'd been talking about. He'd mistaken domestic subversion at the source of Communist success; an opportune Far East journey made him think about the legacies of colonialism and the futility of Dulles' concept of "massive retaliation" as a deterrent to Soviet expediency. "Of what value," he finally asked, "would atomic retaliation be in opposing a Communist advance which rested not upon military invasion but upon local insurrection and political deterioration?" Had Dulles relied on American "advisors" to save Indochina, Kennedy might have avoided that trap, too.

From this and similar themes in the book, it's apparent why Kennedy's fondest admirers were often those who were first exposed to him at a time when he had become something of a finished product. It's equally easy to understand the lingering coolness of many Kennedy colleagues, who watched a callow youth catapulted past them toward the presidency, launched by his father and his father's money even before there appeared to be anything substantial to launch. Parmet, meticulous and detached, aids neither camp; he demonstrates not that Kennedy's character was sterling, only that it had changed.

JFK's meteoric rise did depend on Kennedy wealth, Kennedy connections, Kennedy skill and Kennedy methods (plus a bit of Irish luck) -- and Jack shows precisely how. But Parment also shows that the personal transformation of John F. Kennedy depended, too, on the meteoric rise. Because he had to grow in a hurry, he did -- apparently just in time. Without the excesses, we could not have had the man.