When he was approached by MGM, toward the end of his life, with the suggestion that he should be the subject of a film biography, Jerome Kern was skeptical. He had always carefully drawn a line between privacy and publicity, and his biographer reports that he thought "his scandal-free life was not an interesting subject anyway."

True, he had bought a yacht (named the "Show Boat," naturally), and he had a well-known flair for practical jokes, and he had wooed his wife by playing one of his early songs ("How'd You Like to Spoon With Me?"). But then he had the bad taste, cinematically speaking, to remain faithfully married to her for the rest of his life.

This didn't stop Hollywood, which had already done a number on Cole Porter and another on George Gershwin. A few well-known anecdotes, a bit of fiction and wall-to-wall good tunes were enough for a movie if not for a real life.

Now, at last, the real life is out between hard covers -- the fist major, carefully researched biography of this pivotal figure in the American musical theater -- and as usual, the book is better than the movie. it is less vivid, and the tunes play in your mind rather than on a soundtrack, but it is solid, reliable and thorough. It will tell the serious reader what most needs to be told about Jerome Kern.

Part of what it tells are unrealized possibilities. At various points in his career, Kern was approached to write music for the material that other composers later turned into "Porgy and Bess," "Annie Get You Gun" and "Oklahoma!" And each time he had good reasons for not accepting the project. One can't help wondering what Kern would have done with "Porgy" (with Al Jolson in the title role), just as one wonders sometimes about the operas on "Huckleberry Finn" and "Gone With the Wind" that Kurt Weill was planning when he died. But on the whole, "Porgy" was probably better off in the hands of George Gershwin. Kern had already made his mark on history when that prospect came along, and part of Kern's historic impact was that he made it more feasible for Gershwin to compose "Porgy and Bess" and for Richard Rodgers to compose "Oklahoma!" t

Kern occupies a place in the history of American music something like that of Whitman in our poetry or Mark Twain in our fiction. He caught the American voice, the American flavor, and embodied it in enduring works of art that not only provide deep enjoyment but help to tell ourselves and others something about who and what we are. He was not alone in this effort; others who were converting the American experience into music range from Claude Ives to Irving Berlin. But Kerns did it with a unique blend of artistic integrity and public impact. In its own way, "Show Boat" is a musical monument as significant as Wagner's Ring Cycle. Its opening night -- nov. 15 1927 in Washington's National Theatre -- marks the coming of age of the idiom which is our nation's unique contribution to the world of theatrical music.

Before Kern's arrival, and for the first part of his enormously productive career, there were two kinds of popular music in the American theatre: the operetta, a la Victor Herbert, which tried to match the glories of Viennese operetta, and the musical comedy, a descendent of Vaudeville, which would string musical or comic "numbers" on a thin line of plot like garments on a clothesline. Kern grew up in the latter, native tradition and by his talent raised it to the stature of the imported tradition.

At first, critics were not quite sure what to call it or who should be given the credit. Many of the first notices referred to "Flo Ziegfeld's 'show Boat," giving the producer a kind of credit that had been earned by Kern and Oscar Hammerstein. But at least one music critic, Robert Simon, recognized what was happening. In a long article in Modern Music magazine, he noted the "almost Wagnerian" development of themes and commented that "Kern seems to be at the turning point of his career. If he makes the transition from a sort of operacomique -- and 'Show Boat' is exactly that in the classic sense of the term -- to 'leit-opera' we may finally have opera which is thoroughly and indigenously American." In contrast, Variety found it "muchly overrated" and singled out "Bill," of all songs, for acid comment.

Having opened the door for a new kind of music-drama, Kern stepped through it in his later work, but nowhere near as spectacularly as Gershwin, Rodgers and Hammerstein or Lerner and Loewe. "Roberta," probably his best-known later work, takes a pace or two back toward the Viennese manner, and much of his energy was diffused in later years by his writing for films.

"Show Boat" marked an end as well as a beginning. It was Kern's greatest success, but its run was shortened by the Depression. And it came out almost simultaneously with another landmark, "The Jazz Singer," which film suddenly became a medium for music. The combination of economic problems and competition from film meant drastic changes. Music on stage was no longer mass entertainment. A composer could no longer write a couple of possible hits and a lot of fillers and call it a show.

In his recounting of all this, Gerald Bordman is scholarly in both the best and worst senses of the term; he is thorough, and he had a sense of what is historically important, but his style is rather wooden. The anecdotes are carefully preserved, but told in the style of a teacher rather than a raconteur. More serious flaws are his sometimes loose grammar (he has an imperfect grasp of the distinctions between "who" and "whom") and his omission of a bibliography and discography. Still, he has a fascinating subject and he touches all the bases. The book might make an interesting movie.