BRYCE CANYON is the most beautiful thing in the United States."

That simple declarative statement was made not by a representative of the Sierra Club or Friends of the Earth, but by one of the most noted of composers, Olivier Messiaen.

Two weeks ago in Paris, in the occasion of his 70th birthday, Messiaen's latest symphonic work, "From the Canyons to the Stars," was played under the baton of Pierre Boulez. The 90-minute composition was inspired by Messiaen's 1973 visit to the canyons of Utah. On Aug. 5, 1978, a date the governor of Utah declared "Olivier Messiaen and the Beauty of Southern Utah Day," a mountain in southwestern Utah was renamed Mount Messiaen.

The French composer and his wife, pianist Yvonne Loriod, visited Bryce Canyon for eight days. "We were all alone; it was marvelous," he said. "Apparently one can traverse the canyon on a horse or mule, but I went on foot because it's much nicer that way. My wife took at least 200 photographs. One can stop, take notes, transcribe bird songs. . . " The trip to Utah came about when Messiaen accepted a commission from Alice Tully to write "a work in honor of the United States." He looked through his geography books, of which he has over 7,000 in his home, and said to himself, "The grandest and most beautiful marvels of the world must be the canyons of Utah. So, I'll have to go to Utah." Thus Utah became the place for his inspiration.

Composers have been writing pictorial music for centuries. Vivaldi and Haydn with their portrayals of the seasons had their parallels and forerunners in the Fitzwilliam Virginal Book, with its charming pieces about thunder, lightning and fair weather. The harpsicord pieces of Couperin and Rameau are enlivened with lively sketches of the chirping and calling of birds.

(Marin Marais, who bore the title "violist to King Louis Xiv," once digressed from writing about purely natural phenomena to do a descriptive work depicting the entire surgical process, groans and all, of someone undergoing "the operation for the removal of a cyst.")

The 19th and 20th centuries are filled with purely instrumental works attempting to describe nature in her fair and cloudy moods: Beethoven's Pastoral Symphony with its sudden summer thunderstorm; operatic downpours that occur in Rossini's "Barber of Seville," and "William Tell," Verdi's "Otello," and Tchaikovsky's "Queen of Spades" are only some of the best known. Ferde Grofe, in his Grand Canyon Suite, anticipated Messiaen's fascination with our western canyons by over 40 years.

But no composer in history has, over such a long period of time or in such exhaustive detail, filled his music with passages specifically arising out of his study of nature's colors and birds as has Messiaen.

When he reached Utah's canyons, Messiaen knew how right he had been to choose that part of this country. "It was even more beautiful than in the photographs. It's quite amazing; first, it's so big -- immense; it's a landscape of nothing but cliffs and boulders in fantastic shapes.There are castles, towers, dungeons; there are turrets, bridges, windows -- and then, even more beautiful, there are the colors. Everything is red -- all sorts of reds: red-violet, a red-orange, rose, dark red carmine, scarlet red. . . .

"Colors are very important to me because I have a gift -- it's not my fault, it's just how I am -- whenever I hear music, or even if I read music, I see colors." This aspect of Messiaen is discussed in nearly all of his major works.

"The piece I composed about Bryce Canyon is red and orange," he said, "the color of the cliffs. I proceeded on through the canyons. Next I was at Cedar Breaks. It's a very impressive spot, an immense amphitheater with an enormous slash in the earth, very, very deep -- it is frightening -- and the feeling I had there was religious. I composed a piece entitled 'Cedar Breaks is the Gift of Fear.' Fear in a religious sense. . . .

"After Cedar Breaks I continued on to Zion Park. The cliffs there are also very beautiful, but less red, less fantastic. The atmosphere is more somber, serene, more sacred, even more celestial. I believe that it is indeed celestial, because the Mormons, who discovered this place called it Zion Park.

"So I did like the Mormons and composed a piece which is called 'Zion Park and the Celestial City.'"

It is possible that birds are even more important in Messiaen's composing than colors. "There were the birds of Bryce Canyon," Messiaen said, "birds not to be found anywhere else but there." When Messiaen makes a categorical statement like that, you can believe it, for he has traveled around the world taping birdsongs and can identify and describe them in minute detail. For example: "There is in Bryce Canyon the western tanger, a little bird which is red and yellow with a lovely voice, very flute-like, which sings a combination of three notes (tiot, tiot, tiot). Then there's a very large bird which is called a blue grouse, which goes 'wuh, wuh, wuh,' a strange deep sound which really fascinated me.

"And then there was a bird that was beautiful to look at but with an awful voice. That's just what interested me. It's the Clark nutcracker, black and gray with an incredible voice -- what a racket! If you get three or four of them together, it's like a whole orchestra, a powerful sound."

"At Zion, it was still springtime, the season of love and song for the birds. In Zion there were the most beautiful birds of all. First, and perhaps most important, there was the cassis finch with a lovely voice, flute-like with a charming timbre, a marvelous virtuoso. The bird itself is red. Then there was the gray vireo which is imperative, it's the drillmaster of birds (co-mol) and then a wonderful singer, the western meadowlark."

Messiaen was greatly pleased when he heard that a mountain had been named in his honor. Formerly known as the Lion's Peak and also as the White Cliffs, it stands like a sentinel overlooking the canyons he has put to music. It rises 8,000 feet, and among its geological features are outcroppings of red and white sandstone.

In November there were press reports about the possibility of strip-mining being permitted four miles from Bryce Canyon and of the potential necessity of locating the nation's largest coal-fired power plant somewhere in Utah. Within a short time, public protests began.

When the great French composer returns to the mountain that now bears his name, he will be foremost among lovers of the unique beauties of Utah's canyons -- its colors, its birds, its sunrises and sunsets -- to rejoice at the announcement made in Utah last Wednesday by Interior Secretary Cecil D. Andrus. The new power plant, the secretary said, will be built near Lynndyl in central Utah. It will not be near Bryce Canyon, not near Capitol Reef National Park, not near Zion Park, the "Celestial City." A spokesman for the Interior Department said last Wednesday, "There is no way we are going to permit strip-mining near Bryce Canyon." The air should remain fresh and clear "from the canyons to the stars."