Franz Liszt rushed across the 19th century like a comet, trailing sparks of pure musical radiance. His life had the quality of a fireworks display. Sooner or later, everyone who encountered this extraordinary personality had to stand back and say "aaah," in one way or another, like a crowd watching a light show in the sky -- even those (and they were numerous) who found him distasteful in one way or another.

If he were alive today, Liszt would be a media personality -- a combination of Leonard Bernstein, Vladimir Horowitz and Arnold Schwarzenegger: composer, musical philosopher, virtuoso performer and matinee idol; there would be intense backstage battles between talk show hosts like Johnny Carson and Joan Rivers to exploit his notoriety and personal magnetism.

But he has been dead for a century, and this week in Washington he gets what musical celebrities of the past receive when they have a significant anniversary: a music festival.

Liszt may have been fortunate to have lived in an age when one traveled by horse-drawn coach rather than supersonic jet; the life style of his time enforced a certain amount of sitting quietly and just waiting, thinking.

In the late 20th century, he might have burned himself out trying to realize all his potentials simultaneously. As it was, he packed into his 75 years enough action andIf he were alive today, Liszt would be a media personality -- a combination of Leonard Bernstein, Vladimir Horowitz and Arnold Schwarzenegger. achievement for a half dozen normal lifetimes.

But behind the public Liszt there was an enigmatic, private person who was known to only a few in his lifetime and is still virtually unknown today. It is almost as though he held up that glittering persona to protect the real Franz Liszt, to conceal him from a curious, interfering world.

His life was a mass of seeming contradictions. He was a libertine with amorous conquests ranging from princesses to chambermaids, and he was a religious mystic who actually became a clergyman in his later years. He was a musical showman who carried a bag of cheap tricks across Europe from Italy to Russia. And he was a forward-looking composer and thinker whose influence can be seen in such later, contrasting composers as Gustav Mahler, Be'la Barto'k, and even that other underappreciated genius, Camille Saint-Sae ns. He was a great teacher whose students, following his lead, revolutionized the art of piano-playing.

But the deepest secrets of his technique -- perhaps the essence of it -- went with him to the grave. Was he unable to teach the innermost details of his art or did he choose not to share them? Nobody can say -- but his best students were the first to admit that they could not understand the finest points of his technique.

As a pianist, Liszt could draw from the keyboard sounds available to no other pair of hands -- not only the thunderous chords and lightning-fast arpeggios of the barnstorming virtuoso, but intimate feelings and delicate sentiments comparable with those evoked by Chopin. In this sense, his art -- even when it reeked of show biz -- was intensely personal.

But in orchestral music, where he made a reputation both as a composer and as a conductor, his music was colorfully, blatantly, sometimes vulgarly public. He could make the orchestra sing in ecstasy, roar in anger, tell stories and paint pictures like no other composer of his time.

One can quibble over whether or not he "invented" the tone poem, but he certainly put it on the map of 19th-century Europe with his gigantic, brightly colored orchestral visions. At the other extreme of musical expression, his modest little songs for voice and piano (still not known nearly as well as they deserve) include some items that rank with the work of Schubert and Schumann.

A century after his death on July 31, 1886, Franz Liszt is, in large measure, still one of the major unknown figures of his time. That is one reason why Washington is the scene, beginning today, of a Liszt festival that will try to come to terms with the man in all his dimensions, in words and in music.

According to pianist Jerome Rose, artistic director of the festival, its goal will be "to explore the five facets of his being -- that of a man, pianist, composer, teacher, and minister of God." It will not answer all the questions one might raise about Liszt, of course; the riddle of a century cannot be solved in a week. But the Franz Liszt Centennial Celebration, which begins this afternoon at the Washington Cathedral and continues through June 29 at the Kennedy Center, the Library of Congress, the Smithsonian and St. Matthew's Cathedral, should add a lot of vital new details to the total picture.

Another reason for a festival is that, although he is a great unknown, Liszt is also one of the most popular composers of the Romantic era. Nearly everyone with an interest in classical music knows and loves the Hungarian Rhapsodies, the Mephisto Waltz, the Transcendental Etudes, the two piano concertos and some of the tone poems -- notably "Les Pre'ludes," whose grandiloquent finale was the sign-off music for the "Lone Ranger" radio program.

Devotees of the piano hold Liszt in special veneration. He has a fair claim to be called the composer-performer who understood this complex, recalcitrant instrument most fully and used its almost unlimited potential most effectively.

His piano music may lack the sheer imaginative scope and depth of vision found in Beethoven's final keyboard works, but his Sonata in B minor has (in its very different way) a stature comparable to Beethoven. It is one of the greatest works of art we have from the 19th century in any form or medium -- a perennial challenge to performers, scholars and audiences alike. Other piano works -- the Ballades, Legends, Consolations, Years of Pilgrimage, Legends and operatic transcriptions -- may appeal only marginally to mass audiences. But they are landmarks of the piano repertoire.

Like Liszt himself, the festival will attempt to be all things to all interested parties. Some of the attendees will be students working for academic credit (which will be available through Catholic University). A substantial number of America's leading music critics will be attending under the auspices of the Music Critics' Association. Others will be there for sheer fun and musical bedazzlement.

The scholarly activities -- lectures and master classes -- will be centered, appropriately, on the Library of Congress. One lecturer, Alan Walker, is working on a three-volume biography of Liszt whose first volume has already won several international prizes. Tibor Szasz is not only a brilliant pianist (winner of the 1974 University of Maryland Competition) but a profound musicologist, whose deciphering of the symbolism in the B minor sonata has received international acclaim. Other lecturers include Jacques Barzun, Nicolas Slonimsky and Paul Hume.

Also at the Library of Congress will be an unusual presentation tonight in which the voices of actors and the sound of a piano will combine forces to present a dramatic study of "The Music and Letters of Liszt."

The events at the library will be free, as will a recital by pianist Christopher O'Riley Saturday afternoon, focusing on some of Liszt's less-known music. There will also be free concerts at the two cathedrals, dedicated to the composer's excellent but relatively unfamiliar choral and organ music. Concerts at the Kennedy Center and the Smithsonian will require paid admissions and will include some of Liszt's better-known piano works as well as the neglected vocal and violin music.

But when most people think of Liszt, they think of virtuoso pianists playing virtuoso music. Three of the greatest are scheduled to perform at the Smithsonian: Jorge Bolet, Russell Sherman and Rose, the festival's artistic director. Bolet and Rose are both involved in complete (still unfinished) recordings of Liszt's piano music that have been provoking critical superlatives internationally. Sherman records seldom, but he is a pianist of enormous stature. Significantly, both of the others have deferred to him for the festival's performance of the B minor sonata, Wednesday night at the Smithsonian.

To conclude the festival, all three star pianists will perform, with other festival soloists, in a gala performance next Sunday afternoon at the Kennedy Center.

Only one aspect of Liszt's music will be neglected during this week-long celebration. Not a note of his orchestral music is scheduled for performance, and the epic symphonies inspired by Dante and the Faust legend are worthy of attention.

But these are readily available on records, and the expense of performing them would have depleted the festival's modest budget. Otherwise, it is fair to say that no aspect of the great man's life and work will be untouched in the week beginning today -- at least to raise issues and ask questions, if not to provide definitive answers.