<i> Understanding Toscanini by Joseph Horowitz (Knopf: $30; 472 pp.) </i>

Joseph Horowitz, who gave us the excellent “Conversations With Arrau” in 1983, has set himself a more difficult task here: writing a “fair” assessment from an essentially negative bias of Arturo Toscanini, the Italian conductor (1867-1957) who played such a crucial role in shaping American attitudes toward “serious” music during his three decades of power in this country.

The author, admittedly too young to have experienced Toscanini in any but recorded form, has produced what finally emerges as an intelligent, passionately reasoned study not so much of a man as of an American social phenomenon.

We are taken from Toscanini’s pre-World War I coexistence with Gustav Mahler as top conductor at the Metropolitan Opera, to tenures as an operatic reformer at Milan’s La Scala, to the New York Philharmonic between World Wars (where his rivals included the no less-gifted Willem Mengelberg and Wilhelm Furtwaengler, both of whom he defeated) to the final Years of Sanctification (1937-1954) with the orchestra especially created for him, the NBC Symphony.

Horowitz is at pains to point out that the rivalries were chiefly the handiwork of cultists, above all of the New York dailies’ critics Olin Downes, Lawrence Gilman and later, Howard Taubman, all of whom tended to describe the Toscanini aura (“Toscanini--the priest of beauty, the consecrated celebrant, abstracted, absorbed, awaiting gravely the trembling of the Temple’s veil,” Gilman wrote) and the audience’s reverent attitude toward “The Maestro” rather than his clear-eyed musical interpretations of Beethoven, Brahms, Verdi and Wagner.

The author does show that there were rational voices opposing those of the hagiographers, such as Gilman’s successor at the Herald Tribune, the brilliant, waspish Virgil Thomson. But they didn’t have a chance against the American people’s whipped-up will to own and love Toscanini, a representative of culture but also a man created in their own image: self-made, plain-spoken, objective--a living reproach to pansy Middle-European aestheticism.

This outspoken, courageous enemy of Fascism nonetheless tyrannized musicians who played under him and Horowitz spares us none of the volcanic rages, the willfulness, the personal abuse. Still, to a worshipful America, even to many of his musicians, what was unconscionable behavior in another man had to be forgiven in Toscanini--it was for art’s sake, part of his selfless quest for technical perfection.

Horowitz runs into trouble when, after a few hundred pages (this is a big book), he asks us to acknowledge that “Toscanini was an unquestionably great conductor,” mustering only a handful of examples, from recordings of the 1920s and ‘30s, to support his late-arriving judgment.

Withal, in discussing the recordings, Horowitz comes up with some particularly cogent critical encapsulations, e.g., “Toscanini’s art was based on the overt visceral energies of Verdian popular theater. No conductor more instinctively or thoroughly grasped the suspense of the coiled spring, or the thrill of its sudden, tripped release.” Then, too, Horowitz might have bolstered his case for Toscanini’s greatness by a more probing examination of what in his work so impressed such a wildly varied collection of distinguished younger colleagues as Otto Klemperer, George Szell, Erich Kleiber, Bruno Walter, Fritz Reiner and Herbert von Karajan. More important, surely, than yet another example of Olin Downes’ tub-thumping or Lawrence Gilman’s mystical twaddle.

A principal thesis of “Understanding Toscanini” is that the Toscanini legend--which barely outlasted the conductor’s lifetime--had much less to do with the appreciation of art than with a response to the peculiarly American sort of hucksterism practiced by P. T. Barnum--Toscanini replacing Jenny Lind as the freak, with, as in Lind’s case, “culture” rather than spectacle as the audience’s reward.

The Barnum of this story--albeit without the humor and without the innocence--would then be David Sarnoff, the headstrong, visionary and, like Toscanini, a self-made man who, as president of the National Broadcasting Co. and its RCA Victor phonograph and recording subsidiaries, bestowed Toscanini on the entire nation in 1937 by creating the NBC Symphony, whose Saturday evening broadcast concerts could be heard, free of charge, by Americans of all economic strata and levels of education.

From Toscanini on radio to such mock-cultural extravaganzas as “Great Performances” with Luciano or Itzhak on the tube was only a small, logical step, Horowitz reasons, correctly.

Glass, who is senior editor of Performing Arts magazine, writes the On the Record column for the Sunday Calendar.