THE MOST difficult assignment faced by a music critic is the paradoxical task of trying to describe in words a new piece of music. It is, let us be honest, an impossibility. Why? Well, to put the answer most simply, music is. It exists in and of itself. Music is not words and words are not music. And words cannot be music or replace music or give a reader the slightest idea of music.

One of the simplest cliches in the music critic's craft is to say, "those who were at the concert heard the music and need no words about it. those who were not there cannot possibly imagine the music from any words the writer might set down."

Yet for two centuries and more, journals, magazines, and newspapers have employed writers to write about music; and those writers have, at times, exerted great influence on the world of music, despite all the protestations of the creators, the performers, and the auditors of the art.

The paradox of trying to write about music is intensified by the fact that no two people hear the same music, even though they may be seated side by side at a concert. Whether the music being performed is the First Symphony by Brahms or the brand new "Vicu Siculani" by Marc Antonio Consoli, it sounds different in each listener's ear. Boethius wrote, in the 6th century, "For what need it there of speaking further concerning the error of the senses when the same faculty of sensing is neither equal in all men, nor at all times equal within the same man?"

What Boethius is saying, among other things, and had he the gift of looking ahead some 13 centuries, is that the Piano Conceto No. 5 in E Flat by Beethoven sounds different not only to two people sitting next to each other at a concert, but sounds different to the very same person who may chance to hear it two days in a row. Now the business of writing about that concerto, which is called the "Emperor" in this country and England, is one thing to a music reviewer. He can assume, with considerable justice, especially in a city such as Washington, that most of the people who read what he may write are acquainted with much of the music by Beethoven and probably specifically with that particullar work.

But what is the writer to tell you about this new work, "Vicu Siculani," by Consoli, which last week won the first prize of $3,000 in the new Politis Composition Competition at Boston University's School of Music? It is easy to outline the musical resources required for the new music: the conventional forces of string quintet plus flute, clarinet, and bassoon, supporting a mezzo-soprano. The title is simply Sicillian dialect for "Sicillian Voices." In addition, we have the composer's own discussion in his notes for the work, which tell us that the outer movements are "sturmenti, i and ii," or songs. The first is a love song, in the second the composer emphasizes the Middle Eastern influence in Sicilian music. The whole was meant, in part, "to build a poem concerning my romanticized Sicilian childhood as seen from New York."

All of those details, accurate and pointed though they are, fail to give you one single idea of what the music sounded like.And that is where words fail: in the attempt to transfer to another medium a work of art that already exists complete in itself in its original medium.

It is easy to add that Consoli also calls for the use of a short, native Sicilian flute on which a skilled player can create magical effects by sliding up and down in an unbroken glisando, with an eerie, beguiling sound. It is easy to say that the second movement describes a liturgical processional traditional in Sicily on Good Friday. But none of this can convey to you a single iota of the precise sound of the music.

All of this does, however, bring to mind another fascinating question: What led the four judges, each of them a composer, to select Consoli's "Vicu Siculani" for the first and only prize? Like anyone else confronting a new work, each judge brought his own listening experience -- his knowledge of Beethoven of Brahms, of Monteverdi or Messiaen -- and his personal preferences in musical style and technique, whether for music by Penderecki or Earle Brown, Alberto Ginastea, Roger Sessions, or Claude Debussy.

One certainty is that Consoli's "Vicu Siculani" sounded different in the ears of judge Gunther Schuller than it did in those of judge Mario di Bonaventura, just as it had a different impact upon judge Robert DiDomencia than upon judge Donald Martino.

Another certain thing is that, in choosing "Vicu Siculani" over seven other new works performed in the finals of the competition, the four judges were following a trend that has been unmistakably clear in recent years: The various kinds of so-called experimental music, whether electronic, or music or chance, or of the "musique concrete" variety, are no longer holding center stage. For that matter, that music is holding onto nothing more than the thinnest fringe of attention of cult groups, which is virtually all that it has attracted in the past quarter of a century or so.

This year's Pulitzer Prize in music went to David Del Tredici for his "Memories of a Summer Day," music which one of the Pulitzer judges said, with no trace whatsoever of derogation, "could have been written in the 19th century." The same thing is true of the music by Joseph Schwantner, who won last year's Pulitzer, and of Richard Wernick, who won the year before -- though there is no similarity whatsoever between the musical styles of the three men.

From the evidence of recent composition competitions in this country, where musical currents change more rapidly than they do in europe, this return to musical styles that come to us directly from the great classical-romantic mainstream is today solidly established. Nowhere has that re-establishment been more emphatically stated than by Kryzsztof Penderecki who said, at the time of the world premiere of his opera, "Paradise Lost," in Chicago a year ago November: "I have turned around just about 90 percent from the kind of music I was writing nine years ago." That observation from one of the world's leading composers clearly marks the change of direction in compositional winds.

None of this may make the work of the music reviewer any easier. But it does mean that he will have far less need, in the future, of the "blips and bleeps, the squawks and squeaks" that have been busy signals in the recent past. It may also mean that frames of reference that were for a time of little help to him will again have relevance to his readers as the new cycle in composing techniques asserts itself.