Difficult though it may be to imagine or comprehend, five weeks from today Francis Albert Sinatra will be 70 years old. That's right: The Voice, the leader of the Rat Pack, Ol' Blue Eyes -- the man who a mere 40 years ago had the bobbysoxers squealing in the aisles of the Paramount Theater will actually enter his eighth decade on Dec. 12, 1984. Surely this milestone deserves tribute; and tribute, heaven only knows, is certainly delivered in "Sinatra: An American Classic."

There is no evidence that Ol' Blue Eyes cooperated with John Rockwell or the editors of Rolling Stone in the production of this book, but he hardly seems likely to sic his lawyers on any of them. This handsome, generously illustrated, coffee-table-sized volume is, from first page to last, a love song. Yes, Rockwell does mention Sinatra's "barroom brawls and extramarital cavortings," his "pugnacious macho lifestyle" and his "mean streak," but these are reluctant concessions to the "gangster image" with which Sinatra invariably is identified; these rather unpleasant aspects of Sinatra's public persona are dismissed as quickly and politely as possible.

Rockwell's real interest lies not in Sinatra the man, though he does sketch out a perfunctory biography, but in Sinatra the musician, whom he calls "the greatest singer in the history of American popular music." This claim may well be true, though partisans of Billie Holiday and Louis Armstrong are likely to dispute it with some heat, but it is advanced by Rockwell with such fawning and excessive adulation that it rapidly becomes cloying. It takes a strong stomach to weather much of his prose, most notably the paragraph upon which his panegyric climaxes:

"But if anyone, or anything, is a classic, it is Sinatra. His interpretations have shaped a half-century of song, transforming creativity into audible reality. He has validated an entire vernacular tradition and forced people to recognize its claims to classic status. Beyond all that, through his music and, yes, through his life, he has enriched the very idea of 'classiness': not as something cold and marmoreal, free from human imperfection, but as a living, breathing, loving, hating human being. Art and life have sparred fitfully during this century, with some of the best art recoiling from the horrors of our time. Today we are beginning once again to recognize the place of human feeling in song, and no singer of our time has better invested the widest range of emotion in his music than Frank Sinatra."

Wow. Sort of takes your breath away, doesn't it? "Transforming creativity into audible reality": It doesn't really mean anything, but it sure sounds good, doesn't it? Certainly it will sound good to Sinatra, who will have to rethink his negative thoughts about the gentlemen of the press after reading what this widely respected critic of rock and contemporary music has to say about him.

The pity is that Rockwell chose to say it so breathlessly, for he is indeed an intelligent and knowledgeable critic. Perhaps his problem is that because his own background is in rock, he seems determined to bend over backwards to demonstrate his bona fides in the pop music that preceded it. Perhaps, too, he is frustrated at having nothing really new to report about Sinatra's life and music and thus has resorted to hyperbole by way of padding things out. But whatever the case, "Sinatra: An American Classic" is, even for the reader who greatly admires Sinatra's music, something of an embarrassment.

For the reader who knows little or nothing about Sinatra, the book will provide a brief and useful introduction. The biographical sketch, which seems to draw almost entirely on secondary material, quickly tells the story that is familiar to just about anyone over 40: Sinatra's beginnings in the big bands of Harry James and Tommy Dorsey; his rapid emergence as the heartthrob of millions of teen-aged girls; his precipitous decline in the late '40s; his recovery in the '50s, thanks to an Academy Award for his work in "From Here to Eternity" and a series of brilliant record albums; his various marriages, brawls, and alleged -- but never proved -- associations with the Mafia; his second decline, during the first decade of rock 'n' roll, and his subsequent stirring comeback after a premature retirement in the early '70s.

Rockwell also provides a deft analysis of Sinatra's singing style, one that relies heavily on the pioneering book "The Great American Popular Singers," by Henry Pleasants, to whom Rockwell has generously dedicated his own book. He discusses Sinatra's roots in the Italian bel canto style, his jazz influences, his ingenious use of microphones, his keen (if not flawless) taste in arrangers and accompanists, his respect for lyrics: "The ultimate effect of Sinatra's style, fully evident in the Forties even if it was refined, enlivened and enriched in subsequent decades, is of an utter naturalness, but a naturalness attained through the devices of art."

This is true, though it is not exactly news, at least not to anyone who has followed Sinatra's work over the years. There's no doubt that he's the best of our popular singers, if not necessarily the nicest, and there's also no doubt that his influence on other singers and musicians has been very large. But these are insufficient reasons for conducting a religious service in his honor, which is what Rockwell has herewith done.