THE MOST famous remark ever made about Wagner's greatest opera, "Tristan und Isolde," which today receives its first Washington performance in decades, was the comment of the arch anti-Wagnerian, Eduard Hanslick, Vienna's leading music critic for three decades. Hanslick wrote, "The prelude to "Tristan and Isolde" reminds me of the old Italian painting of a martyr whose intestines are slowly unwound from his body on a reel."

But opposing Hanslick were those -- musicians and laymen alike -- who heard "Tristan" and were never again the same. From France they came to hear it: Giullaume Lekeu fainted during a performance, while Emmanuel Chabrier burst into tears. Henri Duparc and Ernest Chausson returned to France and tried to write music as nearly like Wagner's as possible; while Claude Debussy, at first so caught up in the spell of "Tristan" that he earned much-needed money by playing it at Parisian soirees, later tried his best to write in an opposite manner in "Pelleas et Melisande," only to be found using techniques Wagner had established.

This music first assaulted the world in Munich in 1965. From the beginning, there was indeed something fateful about the whole project. Vienna had seemed, in 1861, the perfect city for the premiere of the "Tristan" Wagner had completed three years earlier. For it was in Vienna that Wagner heard his "Lohengrin" performed for the first time in his life. He had been a political exile from Saxony since the revolutions of 1848 when he had a part in bringing some hand grenades into Dresden, and there had been no way he could get to Weimar to hear Franz Liszt conduct the world premiere of "Lohengrin" in 1850. But in Vienna, the tenor Aloys Ander, who had sung Lognegrin beautifully, became terrified of the demands in the role of Tristan, the Viennese press proclaimed the opera "impossible" -- and after extensive rehearsals, plans for the opera's premiere production there was called off. (And if you want to chart the tragedies associated with the opera, note that Ander died insane in 1864, a year before "Tristan" was finally produced.).

Eventually, "Tristan" had its premiere in Minich, thanks to the patronage of young King Ludgiw II, who was insanely infatuated with Wagner, an infatuation the composer did nothing to discourge in an exchange of correspondence as purple today as when it was written.

On June 10, 1865, in the Royal-and-National Opera House in Munich, "Tristan" was heard for the first time. The world of music was never again the same. Few milestones in the history of music stand out in the eminence that, beyond question, marks the peak occupied by this "Tristan." Beethoven's Ninth Symphony, for its revolutionary ground plan plus the inclusion of solo voices and chorus; Stravinsky's "Sacre du Pringemps," for the way it pulled the rug out from under all previous conceptions of the functions of rhythm -- these stand with "Tristan" as moments when the course of musical events was altered.

Probably those changes effected by Claudio Monteverdi as he moved from the "old practice" of the 16th century to the "new practice" of the 17th were as shattering in their impact on the future of music. But when, on that night in June of 1865, the orchestra of the Royal Opera House in Minich reached the first chord in the now-famous prelude -- it occurs in the second full measure -- the wave of the future could be seen and heard.

Three notes on cello precede it and then:

It is the only chord (see shaded area above) in the world to be known by the name of the opera from which it comes -- it is called, and instantly recognized by musicians everywhere as, the "Tristan Chord." Its spelling -- F natural, B natural, D sharp and G sharp -- has given professional musicians grounds for argument for over a century as they ask, and never agree on an answer, "What is the function of that chord?" As the prelude unfolds, it carries the listener into a world where nothing is ever resolved, not at least until that final radiant chord in B major that comes when Isolde has at last died by the side of her dead Tristan. The blaring C major that closes act one and the doomful D minor chord as the tragedy of the second act ends are no more than ways stations in Wagner's continuing procession of harmonic ground-breaking.

And ground was broken in this opera. So direct does the line seem today from Wagner to Schoenberg and the coming of atonal centers of harmonic thought that it is hard to remember that there were and still are those who do not see it as a clear, unbroken procession. The Prelude to "Tristan" offers no single moment of rest or repose when you can think, "Ah! At last a consonant resolution." Because even in those rare fleeting moments when a chord is completely at rest, it is instantly set upon by a suspension, a dissonance, those notes that Berlioz called "the long appoggiaturas that replace the real note" and "only increase the cruelty."

In these measures can be found the seeds of all that we know today as unending chromatic harmony, atonal music, and finally 12-tone music, all deriving from the scale you can easily find by playing every black and white key between middle C and the C an octave above it. You then declare each of those notes to be equal in value in the musical hierarchy.

Once the terrifying "Tristan" was performed, it opened up what for a time seemed a frigtening vista: The husband and wife, Ludwig and Malvina Schnorr von Carolsfeld, who first sand the roles of Tristan and Isolde, were doomed.

First of all, Malvina developed a sore throat on the very day of the premiere (May 15, 1865), four days after the dress rehearsal. That put off the premiere until June 10. One month later, Ludwig, the first man to sing the role of Tristan, died. "For me he lived; for me he died," Wagner said a year later. Had the exertion of preparing and singing the arduous role brought about the tenor's death" Probably. Soon after his death, Malvina, like the widow of Alban Berg generations later, began to experience nightly visitations from her dead husband, telling her that she should become all-in-all to Wagner. Four years later, conductor Hans Richter's favorite assistant conductor, Hans Everle, broke down during rehearsals for "Tristan," and went into an insane asylum. And, perhaps, incidentally, King Ludwig also ended up being declared insane.

By general agreement, admitting all the grandeurs of "Die Walkuere" and "Gotterdaemmerung," it is "Tristan" that stands as Wagner's suppreme achievement. It is, interestingly enough, his one opera that requires neither ballet, large chorus, nor special effects. What it does require is a magnificent orchestra and a cast of singers who have both voices and brains.

Two sopranos, famous in the role of Isolde, have added personal comments about the opera. Birgit Nilsson, the most celebrated of recent Isoldes, once told a yound soprano who asked what was required to be a satisfying protagonist in the part, "A pair of comfortable shoes!" And Helen Traubel, one of this country's best-known sopranos in the famous role, once remarked, in reference to her own substantial size, that when she and Laritz Melchior, the world's most admired Tristan, rushed together in the second act of the opera, it was "like the head-on collision of two Fifth Avenue buses."

The title roles are long -- though the opera is by no means the longest to be heard regularly these days. Both "Parsifal" and "Gotterdaemmerung" outlast it. Nor does Isolde have nearly as many high Cs to sing as does, for one example, Alda, or for another, Violetta, in "La Traviata." Isolde has exactly two top Cs in her part, both of them at the peak of her meeting with Tristan early in act two.

But time has made it unmistakably clear that heroic voices are essential. The procession of great sopranos who have sung it at the Metropolitan Opera alone illustrate that: Lilli Lehmann, Lilian Nordica, Olive Fremstad, Milka Ternina, Frida Leider, Kirsten Flagstad and Birgit Nilsson are goddesses of operatic history. Strangely enough, and as if continuing that ominous tradition that began when Ludwig Schnorr von Carolsfeld died soon after taking on the role of Tristan for the first time, the world has never been crowded with great tenors in the part: Jean de Reszke was indisputably superb, but among those who succeeded him at the Met were many who are happily forgotten for the sorrowful bleatings and strained sounds they put out. There was one whose name remains unchallenged by any: Lauritz Melchior. For years, he sang a Tristan that combined velvet and steel with a manner of knightly courtesy unrivalled since the opera was first heard (according to the testimony of Alexander Kipinis, who heard or knew closely of every major Tristan). Since Melchior, Jon Vickers has come closest to that lofty projection of sound and manner necessary for a great Tristan. That's not very many in 115 years.

There have not been many staged performances of "Tristan" in this city. The last, if my records are correct -- and I believe they are in this case impeccable -- was in 1929, when on Tuesday, Feb. 5, at 7:45 p.m. in Poli's Theater the German Grand Opera Company -- S. Hurok, managing director, if you please -- presented "Richard Wagner's Der Ring des Nibelungen: 'Die Walkuere,' Feb. 4: "Tristan und Isolde, Feb. 5; 'Siegfried, Feb. 7, and 'Gotterdaemmerung' on Feb. 9. I telephoned the other day to Sonia Sharnova, who was the Isolde in that distant time, and asked her if they really gave "Tristan" as part of the Ring Cycle. Today Mme. Sharnova, who was distinguished as Brangane, Fricka, Maagdalena, and in many other leading roles, lives and teaches actively in Chicago. She said "Yes, they did. I suppose they thought it would sell more tickets thay way."

A word of caution: Once "Tristan" starts, there is no time when you can be seated until the entire first act, prelude and all, are over. And the first act runs about an hour and a quarter.So why not get there ahead of time to the Washington Opera's production? That is, after all, a work that changed the course of music. And it's worth every minute it takes.