MEMBERS OF the National Symphony Orchestra, unanimous in their high praise of Erich Leinsdorf as a conductor, are nonetheless quick to mention his caustic wit and ample ego. One instrumentalist likened a Leinsdorf rehearsal to a trip to the dentist: you don't always enjoy yourself, but you feel better afterwards, and you certainly recognize the value of undergoing such rigorous experiences from time to time. Much the same sort of thing can be said about Leinsdorf's latest literary effort. It is indeed a similarly rigorous experience -- so much so that the book will be fully comprehensible only to musicians at ease in reading a full score and conversant in the language of orchestral playing and orchestral rehearsals. It is, in fact, a textbook for conductors.

This is not to say that The Composer's Advocate is turgid and abstruse. Musicians will find it concise, witty and rewarding if they are willing to follow Leinsdorf's detailed, measure-by-measure analyses. It is the depth of Leinsdorf's knowledge that is the book's greatest strength. Here is a musician equally at home in piano music, string quartet, opera and symphony. And Leinsdorf's repertoire is as broad as it is deep. Far from being a specialist in the German symphonic tradition of which he is a part, his tastes run from Bach and Schoenberg to Verdi and Prokofiev. With dazzling skill, Leinsdorf conjures up musical examples as diverse as a Brahms song, a late Beethoven quartet, a Debussy nocturne, or a Verdi opera.

It is a rare musician indeed that can address the problems of style in such a wide range of music, and Leinsdorf's accuracy is unfailing. The wonderfully detailed and insightful analysis of tempos in the famous second act Finale to Mozart's The Marriage of Figaro is expected from a conductor like Leinsdorf. But his insights into Debussy's style, his advocacy of Verdi's metronome markings, and his admiration for Puccini's organizational skills are all refreshing bonuses. (Leinsdorf's free translation of Debussy's instruction in Fetes, "et toujours en s'eloignant davantage" as "until the whole magic is lost in the distance," captures the essence of the music perfectly.)

Clearly, Leinsdorf is a musician of awesome resources, and his advice to those in the business is of great value. But, like the dentist's drill, Leinsdorf's caustic criticisms spare no one. Clearly relishing his mission, Leinsdorf sets himself up as resident iconoclast and proceeds to debunk everyone from opera directors and musicologists to conducting students and recording engineers, not to mention his colleagues in the conducting and performing world. While this is done with a quick wit, the results are mixed. His criticism of some contemporary opera directors for their unjustifiable tendency to "reinterpret" masterworks (The Flying Dutchman staged as a dream in the Steersman's mind, for example) rings true. No one would dare make such musical revisions -- why then is the drama fair game? On the other hand, his dismissal of the eminent musicologist H. C. Robbins Landon is unfortunate and misguided:

"There are some much-touted 'last word' editions of Haydn that are accompanied by reams of learned notes; yet in the score of one of this master's greatest symphonies, many egregious errors have been left standing without a word from the editor."

What Leinsdorf seems not to realize is that he is asking Robbins Landon to do just what editors have been criticized for doing for years, namely, to correct the composer's inconsistencies. That the Landon edition preserves Haydn's originals, warts and all, is precisely its greatest asset. The conductor is then forced to decide what Haydn wanted, and using the good judgment and common sense that Leinsdorf advocates throughout his text, make the necessary revisions himself. If Landon had done this, and his revisions had not coincided with Leinsdorf's taste and judgment, he would surely have been blasted from the other side! This kind of criticism inhabits every page of the book. However much one is inclined to agree with Leinsdorf's notions, the constant ridiculing of others' performances and ideas becomes tiresome. One is soon dulled by the constant train of anonymous "famous" tenors, "well-known" pianists, and artists "widely regarded as Mozart experts," all of whom debase and mangle the classics in Leinsdorf's eyes.

Perhaps all of this gossipy information was included to help make the book appeal to a mass audience. It becomes a perverse game to figure out just who it is that Leinsdorf is criticizing. It starts with the book's opening paragraph:

"Long ago, I spent several weeks in Salzburg, living at a modest inn on the outskirts of the city. I was thrilled when my next-door neighbor turned out to be an up-and-coming young conductor who was music director of an important American symphony orchestra. We talked a great deal, and when we retired after luncheons I could hear through the wall the music from his portable phonograph. Often the same side . . . was repeated over and over. By the time my neighbor departed I had figured out that these sessions with the Victrola were preparation for his winter season's repertoire. I was 22, green and provincial, and yet my original awe at having met a real chief conductor of an American orchestra turned into puzzlement. Why should a man of such eminence need to learn his music from repeated hearings of other performers?"

Now who might that be? Or perhaps what is at work here is just the legendary ego of all great conductors. In his advice to young conductors, Leinsdorf admonishes them to have no delusions about themselves, "When a young (or old) conductor steps before an orchestra, he is sometimes thinking, 'Now they will play this work for the first time as it should be played.' This may be accurate self-assessment or it may be megalomania." Yet, a few pages earlier Leinsdorf addresses the problem of the opening of Beethoven's Fifth Symphony. The problem, simply stated, is why did Beethoven add an extra bar to the second long-held note of the famous opening motto. Leinsdorf writes, "I have asked every musician I could find what Beethoven meant by that 'extra' bar. . . . One day, on a flight from the East to the West Coast, I devoted the entire journey to this enigma and came up with an explanation that still appears to me to be the only one that answers the question." Such things are better thought privately than claimed publicly.

That Maestro Leinsdorf is an extraordinarily astute and sensitive musician is evident on every page of The Composer's Adovcate. Musicians will find his insights profound and his ideas compelling. What a pity, then, that he feels such a compulsion to show that he is always right, a true thinker surrounded by more vulgar or less enlightened colleagues.