MADEMOISELLE; Conversations With Nadia Boulanger. By Bruno Monsaingeon. Translated from the French by Robyn Marsack. Carcanet. 141 pp. $14.95.

LEARNING THE CRAFT of composition more often than not requires a guide. All musicians try to find the teacher who will nurture solidity in musical ideas and train a discerning ear through harmony, counterpoint and analysis. The most fortunate also find a teacher whose love for music is infectious, whose standards are uncompromising, and who inspires the student to seek out beauty in all musical pursuits.

Nadia Boulanger was such a teacher. For six decades, until she died in 1979, she taught generations of composers and performers.

Descriptions by Virgil Thompson and Aaron Copland (they leap first to mind, although there are numerous others) from scattered sources offer some insight into Boulanger's charisma and her unique influence on composers. Yet, as fascinating as those memoirs are, reading them makes one long to hear an extended cadence of Boulanger's own words. Happily, Bruno Monsaingeon's Mademoiselle, recently translated from the French by Robyn Marsack, provides just what one might hope for: a compilation in conversational tone of Nadia Boulanger's thoughts on life and music.

These interviews, or "intermittant encounters" as Monsaingeon calls them, took place in the last five years of Boulanger's life. They have been judiciously arranged by topic into a reconstructed dialogue form. Only occasionally do Monsaingeon's proddings interfere with what otherwise seems a natural sequence of Nadia Boulanger's reflections -- now stentorian and intense, now warm, humorous and gentle, but always conveying her unwavering moral sense.

The rigorous thought for which Boulanger was known in her teaching are everywhere apparent as she discusses issues and people of great importance to her. Each of her anecdotes about her musical background -- her study with Faur,e, her devotion to the music and memory of her sister Lili, what she considers cardinal virtues, and what she expects from students -- serve more than an evocative or description function. A story is told not only to entertain but to illustrate some firmly held conviction or universal principle. Oddly enough, this didacticism coupled with her disarming modesty is very attractive and never sounds dogmatic or pious.

When speaking of her father's musical encouragement and the effect of his death in her early childhood, Boulanger remarks, "If we bring the past with us, it remains present and clarifies the present. If we forget, we have nothing. Everything is obliterated."

Later she echoes that refrain discussing the evolution of musical styles. "You play Stravinsky's Capriccio and at the end you know it's in G. Is it the same thing as a symphony by Haydn? No, but there are a lot of points in common. Each successive stage brings something new which has its own value, but there is no genius without ancestors."

No piece of music was radical to Boulanger's ear. There were always coordinates to locate relationships to the whole history of musical development. Her enthusiasm for the music of such diverse composers as Stravinsky, Copland and later, Xenakis, attests to her uncanny ability to recognize a singular voice and her commitment to understanding that voice. Engrained habits of listening were anathema to Boulanger and she programmed Monteverdi in a period when Renaissance music was not being performed.

In several instances Monsaingeon intrudes to needle Boulanger into giving her final word on the Second Vienna School and Schoenberg's 12-tone method. It seems unnecessarily artificial a prompting. It is also a spur that tries Boulanger's patience and ignores her oft-made point that genius supersedes whatever methods ie at its disposal. She stresses that compositions should be approached on their own terms, not as examples of any particular school. Though Boulanger hails Berg's Wozzeck as a major 20th-century work, she freely admits to being bored by his opera Lulu. She is reluctant to participate in any trend trying to assign a hierarchy of composers.

One wonders why Monsaingeon presses Boulanger about her abandonment of a career in composition. Her initial response doesn't beg psychological embellishment. Boulanger felt as a young woman that her gift was not in composition and that her music, while possibly pleasant, lacked larger ineffable dimensions. What is more remarkable is that from a very young age -- perhaps due to her deeper faith in Lili Boulanger's compositional talent -- Nadia Boulanger used her phenomenal musical intelligence to chart her role as a supporter, guardian and guide for others.

AS A POSTLUDE to these talks, Monsaingeon invited Murray Perahia, Leonard Bernstein, Yehudi and Jeremy Menuhin and others to write tributes expressly for this book. Robyn Marsack's supple English translation includes a touching introduction by Elliott Carter. Inexplicably, the English edition omits an encomium to Boulanger written in 1967 by Saint-John Perse, the photocopy of which was published in the French edition.

This slim volume is a valuable contribution to the existing works by and on Boulanger. To dip into it at any point is to understand why Paul Val,ery fondly referred to her as "Music in Person" and why Nadia Boulanger became a cynosure for some of the greatest musical personalities of our century.