THE JAZZ AGE Popular Music in the 1920s By Arnold Shaw Oxford. 350 pp. $19.95

THE 1920s, Arnold Shaw writes, "were a crucial period in the history of popular music, as significant musically as the fifties were with the advent of the 'rock revolution.' " Like much else in The Jazz Age, that observation is both useless and careless. However much the "rock revolution" may have changed popular music, its effects are trivial compared to those of the musical revolutions of the 1920s. Certainly the coming of rock 'n' roll altered popular music, for better and for worse; but the developments of the 1920s accomplished nothing less than the creation of 20th-century popular music itself, without which there could have been no "rock revolution."

The music of the '20s is a wonderful subject for a book, so more's the pity that Shaw has made an utter botch of it. Neither his sincerity nor his credentials are in question; he loves American popular music and has written about it for years, though with rather less distinction than his publisher would have us believe. But in The Jazz Age he has done little more than assemble lists -- of song titles, musicians, theaters, composers, nightclubs, what have you -- and string them together with perfunctory, cliche'-swamped prose; the book contains no serious attempt to summarize and assess what happened during the 1920s, and precious little effort to figure out why it happened.

Properly told the story would contain many ingredients, but all of them could be boiled down to two central themes: urbanization and modernization. American popular music as we now know it evolved because during the years between the wars the nation moved from the country to the city and because the rapid development of technology made it possible for music to reach a mass audience. From time to time we get a glimmer of these themes in Shaw's chronicle, but he is so fixated on the dogged compilation of the trivial that for the most part it is up to the reader to detect them for himself.

It isn't all that difficult to do so. Jazz -- which Shaw treats in a surprisingly offhanded fashion -- was begun by black musicians with country roots who played first in New Orleans and Kansas City, then moved northeast to Chicago and New York, a passage that reflected in microcosm the great black northward emigration from southern poverty and discrimination. It was by congregating in these cities that black musicians influenced each other, and it was here that they introduced their music to the whites who subsequently bowdlerized and popularized it. The origins of jazz -- the blues in particular -- may lie in the country, but without the city the music almost certainly would have died soon after birth.

The same is true for what is commonly thought of as the "popular" music of the '20s: the music of Gershwin and Kern, Porter and Rodgers. It is music that derives from many sources, but above all it is an urban music; not merely does it have the sophistication and wit of the city, but it is a compendium of all the music that had congregated there. These songwriters and performers, a large percentage of whom were first- or second-generation Jews, blended their own musical heritage with the music they heard in the city, jazz especially, and produced a style that was distinctly, not to mention inimitably, urban-American.

But important though the city was, the musical revolution of the '20s could never have occurred without the coming of technology. Recordings, radio and movies -- these were the great inventions that made it possible for the music of the countryside and the music of the stage to become truly national. Shaw does mention "the devastating impact of radio and records on the active piano-playing generation" -- a by-no-means unimportant point that, characteristically, he fails to explore -- but he devotes amazingly little attention to the watershed effects that these developments produced.

Thus he dutifully notes which songs became gold-record successes in the marketplace, but apparently it never occurred to him that until the '20s gold records were nonexistent because there was no such thing as a system for the mass distribution of phonograph records. When that system came into being, it changed American music forever. It mandated the three-minute performance, with incalculable consequences for both jazz and popular music, and it enabled music-lovers to hear performers whom they had never seen in person, while at the same time it spelled the end of widespread home performance. Along with radio and the movies it killed off vaudeville and burlesque. It was the beginning of the new age of home entertainment, and of the mass culture that arose to produce this entertainment.

WE GET little about this from Shaw, and for that matter we don't get much about what the music sounded like -- about how it differed from the folk and popular music that preceded it, or about what its own distinct qualities were. Only from time to time -- as in his discussion of "Yes, We Have No Bananas!," of all things -- does Shaw pause to consider a composition's musical ancestry. Otherwise he is content to compile interminable lists of songs, perhaps assuming that their melodies will immediately leap into the reader's head; it is no small measure of how deeply the music of the '20s entered the national consciousness that in fact most of them do just that.

But for the hows and whys of this the reader must look elsewhere, to books by Henry Pleasants and Alec Wilder and Nat Hentoff and Wilfrid Mellers and others who have written thoughtfully about American music. Shaw quotes them -- he peels off quotes by the dozen, in fact, as though preferring the judgments of others to his own -- in his plodding progress through the decade, just as he indulges himself in pointless non sequiturs and digressions, but he does not manage to make it all add up to anything we did not already know. ::