Some of the world's Liszt scholars' and enthusiasts have been meeting in Washington for the past three days under the pennant of the American Liszt Society, exchanging numerous details about the life and music of one of the most extraordinary musicians who ever lived.

They will know, for example, that what the Princess Cristina Belgiojoso really said back there in Paris in 1837 was not the often-repeated "Thalberg is the best pianist in the world and Liszt the only one." What the princess actually said is far more laudatory: "There is only one Thalberg in Paris, but there is only one Liszt in the world."

The princess was referring to Sigismund Thalberg, one of the giants of the piano in those amazing days when Chopin was also setting Paris on fire, playing his own music. It was that same Thalberg to whom Clara Schumann, compared Liszt -- and Schumann, who was by far the greatest woman pianist of those days, could be scathing on the subject of Liszt when she felt it: "Beside Liszt, other virtuosos appear so small, even Thalberg." Schumann added, "No artist except Paganini possessed, to so high a degree. as Liszt, the power of subjugating, exalting an audience."

No wonder Hector Berlioz wrote, after hearing Liszt play Beethoven's "Hammerklavier" sonata, that "Liszt, in thus making comprehensible a work not yet comprehended, has proved he is the pianist of the future. Until now this has been the Enigma of the Sphinx for almost every pianist. Liszt, another Oedipus, has solved it in a manner that would have sent quivers of pride through the composer."

These stories are part of the life of the man who was -- oh dangerous superlative! -- the greatest pianist in history. About Liszt the composer, however, arguments still rage -- although some of them could be settled fairly peaceably if only more of Liszt's music were performed.

Students of Liszt are still finding new source materials and corrected data from which to construct more detailed, accurate accounts of the life of this amazing man. One of the most valuable recent books is Beth Archer Brombert's biography, "Cristina, Portraits of a Princess." This is a brilliant canvas of the years in which Liszt, who was one of the great lovers in musical history, may well have included Cristina Belgiojoso among his long list of mistresses.

It was she who brought about the composition of the "Hexameron," a series of variations on a march from Bellini's "I Puritani," written by Liszt, Chopin, Thalberg, Henri Herz, Carl Czerny and Johann Pixis. The composers wrote it so that the proceeds from its publication could go to needy Italian exiles.

It was with the princess that Liszt invested funds to revive a bankrupt newspaper, La Gazzetta Italiana, and it was with the princess that Liszt frequently talked about buying a house in Locate, Italy. Brombert cautiously goes no further than to say that such a liaison was "not impossible."

Liszt was, in Brombert's words, "not a man like any other." He was a force of nature, magnetic, irresistible. His overwhelming sexuality caused women in his audience to faint, to sigh, to scream, in some cases even to fight over a memento.

But the moment for a lasting Liszt-Belgiojoso affair passed with no clear sign of it ever having occurred, when Liszt turned from the Italian princess to the Polish-Russian Princess Carolyne Sayn-Wittengenstein, with whom he lived for years, and whom he for a time he hoped to marry.

Her name will probably come up at the Library of Congress this afternoon when Edward Waters, the former chief of the music division of the Library of Congress and one of the world's top authorities on Liszt, gives a talk entitled "Presenting Mrs. Franz Liszt."

Liszt specialists will be finding new material of the highest value in a book published here in Washington only four months ago. It is "the Letters of Franz Liszt to Olga von Meyendorff, 1871-1886," published by Dumbarton Oaks, where the letters have resided for 22 years.

The Baroness Olga von Meyendorff was 27 years younger than Liszt, one of four women with whom he carried on a voluminous correspondence in his last years. She was the last person to whom Liszt wrote before his death in Bayreuth on July 31, 1886.

Liszt wrote to the baroness in French, one of his preferred languages. Bought for Dumbarton Oaks in October 1957 by its late, gracious chatelaine, Mrs. Robert Woods Bliss, the letters only recently were translated by William Royall Tyler, former director of Dumbarton Oaks. Previously unpublished, they throw new light on Liszt, fill in some long-unexplained chinks in his story and add a new dimension to our knowledge of his final 15 years.

Among these hundreds of letters is this memento of the Princess Cristina: "This brings to mind a rash step by Princess Belgiojoso who, in order to please a friend, had done her the favor of writing a few lines of introduction for her roughly as follows: 'Mme. XXX is a ridiculous and even insufferable nincompoop. She'll tell you that she and I are on intimate terms -- try to get rid of her politely.' Unfortunately, her friend opened the letter before she should have."

Those who study this new cache of letters will find Liszt's opinions, at an advanced age, on religion, Parsifal and new as well as familiar music of his time.

So Washington is not only playing host to the Liszt Society, but has also provided it with some of the most valuable historical materials to come to light in years.