AS CHRONICLER of the avant-garde for The New Yorker, Calvin Tomkins has specialized in rendering the esoteric doings of artists comprehensible to a reader whose initial reaction to the art might be suspicion or hostility. His quiet, meticulously detailed prose is the voice of reason calmly explaining the work of madmen. Here then Calvin Tomkins seems to have found a subject well suited to his special gifts. Robert Rauschenberg has been the bete noire of the gallery-goer since the 1950s when he first exhibited what some considered neo-dadaist ravings -- his bed dripping with paint, a stuffed angora goat with a tire around its middle, collages of newspaper and magazine photos placed in bewildering juxtaposition. More than most visual artists, Rauschenberg has led a life of high drama, enhanced not only by the flamboyance of his work but also by his involvement of his work but also by his involvement in social and political causes and the performing arts.

There are such interesting possibilities in this coming together of author and artist that it is a shame that the result is flawed. Tomkins has not made the leap required when a writer changes the scale of this work from that of a profile to a book-length study. Unable to sustain the narrative thread, Tomkins gives the reader a tantalizing sketch of Rauschenberg sprinkled between the pages of a bland, unnecessary history of the New York art world during the last 25 years.

The early days are the best part of the text, before Rauschenberg enters the larger world and the flow of the story is diverted. Born in Port Arthur, Texas in 1925 to a German-born father and a Cherokee mother, Milton (as his parents named him) did not see a work of art until he was almost 20 years old. The arts were not discused in a family whose life centered around the light and power company that was the chief source of income for the town and the hunting and fishing that the senior Rauschenberg enjoyed in his leisure hours. Milton did not distinguish himself in school, nor was he popular with his peers. In fact, the only aspect of the adult to be found in this portrait of the early years is Rauschenberg's fearles disregard for the opinion of others and his bizarre sense of humor. Tomkins relates how Rauschenberg ran for the presidency of his senior class:

" 'I liked the ridiculous notion that anyone as unpopular as I was should do that,' he recalls. His campaign was novelty itself. One day he brought his pet goose to school; he went around releasing it in a room where a class was in session, shouting 'Vote for Rauschenberg!', then running around to the other door to catch the flustered goose coming out. . . . Most of his classmates were simply bewildered by his electoral tactics, and he got only two votes."

After high school, Rauschenberg spent six months studying at the University of Texas at Austin's school of pharmacy before enlisting in the Navy. He was a successful sailor, happily surrendering to the routine. He even enjoyed his time as a neurospychiatric technician when, as Rauschenberg later said, "I learned how little difference there is between sanity and insanity and realized that a combination is essential." It was also during this period that Rauschenberg discovered that he had talent for drawing and painting -- his portraits were in demand among his colleagues in the military -- and "that there was such a thing as being an artist." This revelation occured at the Huntington Art Gallery in California when Rauschenberg saw his first works of art, those celebrated chestnuts: Pinkie by Thomas Lawrence, Gainsborough's The Blue Boy, and Joshua Reynolds' Sarah Siddons As the Tragic Muse. From there, the encouragement of a friend and the G.I. Bill took him to the Kansas City art Institute (where he decided to call himself "Bob" because it was a "perfectly common" name and, in 1948, to Paris.

Abroad he met Susan Weil, a New York art student who was to become his wife and the mother of his only child, Christopher. Her more sophisticated tastes introduced Rauschenberg to the stimulating enviroment of Black Mountain College and, ultimately, to the New York art world. From this point on, the story becomes more familar, the pace accelerates -- Rauschenberg's early struggle, his frienship with Jasper Johns, collaborations with composer John Cage and choreographer Merce Cunningham, his successful affiliation with art dealer Leo Castelli. In an astonishingly short period of time, Rauschenberg transformed himself from the rawest of neophytes to the dominant figure in postwar painting. He did it by creating work that exemplified what critic Tom Hess saw as a "shift from aesthetics to ethics; the picture was no longer supposed to be Beautiful but True -- an accurate representation . . . of the artist's interior sensation and experience. If this meant that a painting had to look vulgar, battered, and clumsy -- so much the better."

This story on its own has the energy to carry the book. Tomkins, however, feels compelled to write the art history of the time as well, devoting chapters to such topics as Abstract Expressionism and Pop Art. Rather than seeing this material from Rauschenberg's perspective, Tomkins attempts to write "straight" art history; but since the author is not a historian, he relies on the standard texts. The result is a restatement of familiar material which, at its worst, is little more than a chronology of key moments in modern art. The impact of this rehash of history on biography is deadening. After a while Rauschenberg's like appears to be little more than a series of bulletins breaking into the flow of events. Suddenly, for example, the reader is told that "Bob was drinking a lot." But, because the development of character was abandoned several chapters back in favor of the development of Rauschenberg's art and contemporary art in general, the essential connection between the artist's life and work is lost.

Curiously, this distance from Rauschenberg as a person is accentuated by a trait that was very valuable in Tomkins' profiles. The cool, neutral style that works so well in The New Yorker seems at odds with a full-length biography and with Rauschenberg himself. Because there are no crescendoes, no big moments in the writings, nothing propels the story forward, and the artist himself is diminished. When something occurs that is downright weird, it appears, in Tomkins tasteful prose, to be merely eccentric. Passion becomes mild tension.

Tomkins to also far too reticent about Rauschenberg's personal life. For example, the break-up of his marriage and the love affair with Johns -- the change from hetero-to homosexuality -- deserves more attention and analysis. What the reader is left with is a problem of definition. If Tomkins intended to write a history of the period with Rauschenberg as the symbol of the era, then a fresher perspective was needed. If this was, in fact, to have been a biography, then Rauschenberg has not been allowed to emerge from the background, his genius and complexity is never fully explored.