SOMEWHERE IN the files of the Mayflower Hotel there reposes -- assuming they kept duch things -- a bill for room service signed, "Thomas Beecham, Bart." But Sir Thomas did not sign it.I did.

How could such a thing happen?

It all began in Constitution Hall on a cold December night in 1946. There was a performance of "Ai da" with Zinka Milanov in the title role. A few days earlier Philip L. Graham, the publisher of The Washington Post, had suggested that I take a crack at being a music critic in place of Ray C.B. Brown who had retired after 17 years of reviewing. The Grahams had been carrying on a nationwide search for a new critic. In fact, Katharine Graham was off consulting with Aaron Copland about potential candidates. But Phil Graham was stung into action by a review of the Philadelphia Orchestra written by a city room reporter (a common custom in those days) that included this: "Eugene Ormandy is a very versatile conductor. Sometimes he conducts with his left hand, sometimes with his right hand, and sometimes with both."

In 1946 I had been music director of The Post's radio station, WINX, which was at that time the only "good music" station in town. Graham thought I should move over to E Street (then the site of the Post building) and start writing reviews and articles. I have been at it ever since. A week ago last night, after the National Symphony Orchestra's triumphant concert in the Royal Festival Hall in London, I telephoned a story to The Post. That review is the last one I will write as music editor of the paper. Others that may follow will be by The Post's music editor emeritus.

It has been, for the most part, a marvelous 36 years. Imagine growing up loving music and then finding out unexpectedly, at a tender age, that, as the late John W. Suter, dean of Washington Cathedral, once said in a sermon on beauty, "There are even newspapers and magazines that pay people to tell us whether or not what we heard last night was beautiful." He added, "Oh, they don't pay them a whole lot!"

That performance of "Ai da" was the starting point for 3 1/2 decades of professional listening to music, writing about it, teaching it, trying to explain its mysteries to nonmusicians, getting to know some of the greatest musicians in history, and always loving music more every day. One of the questions most often asked of music critics is, "But don't you ever get tired of music?" to which the only possible answer always was, and always will be, "No."

Obviously, there wasn't such a vast amount of music in Washington 36 years ago as there is now. But it is also true that Washington was by no means the musical wasteland some Johnny-Come-Latelys love to depict. From the very first, my beat included the Library of Congress, where the Budapest Quartet was at the peak of its form, playing the repertoire, old and new, in ways no other quartet has approximated. There were the Phillips Gallery and the National Gallery with their emphases on younger artists and less familiar music. In those days the Phillips presented concerts not only on Sunday afternoons, but also on Monday nights, and Richard Bales was already making history with his annual American Music Festivals.

And there was Constitution Hall. It was not what the capital of the country should have had, but that did not keep it from being the site of unforgettable concerts by Arthur Rubinstein and Vladimir Horowitz, who never forsook the big hall for the newer glamor of the Kennedy Center. In Constitution Hall, The Post's reviewer had tickets for M1 and 3. They had been Brown's seats and they became mine, just as H101 and 102 in the Coolidge Auditorium at the Library were, and remain, the seats for The Post's critic. (The only drawback to this kind of thing is that people quickly realize they can corner a reviewer when they want to argue a recent review, or check to see if he is reading French philosophy--a habit Ray Brown refused to drop.)

Some of the greatest music I ever heard was performed in Constitution Hall. Arturo Toscanini, rehearsing the NBC Symphony there on a coast-to-coast tour, brought tears to the eyes of his first viola, Milton Katims, with the beauty of his direction of Debussy's "Images."

And Marian Anderson, once the Daughters of the American Revolution got over their disastrous faux pas, sang her most glorious Washington recitals in that hall. Another singer whose music-making still lingers in the framework of that 3,842-seat auditorium is Gladys Swarthout, with her gorgeous, little-known Italian repertoire. And Jennie Tourel, who sang "Down in the Forest" by Landon Ronald, and later told me it "might have been, from the purely vocal standpoint, the best singing I ever did."

It was in Constitution Hall that Lotte Lehmann sang a duet recital with her adored Lauritz Melchoir when, after one of the irresistible duets by Schumann, she stood on tiptoe to kiss the cheek of the great Dane.

There was another hall, too, one that no longer exists, Continental Memorial Hall, which stood behind Constitution Hall. Today it houses the DAR archives, but one year it was the scene of a series of three memorable concerts: Wanda Landowska, Elisabeth Schumann and Alexander Kipnis. Not bad taste for a "backwater."

And you don't talk about Constitution Hall without remembering Maria Callas there in concert with orchestra the night she ended the program with the entire final scene from "Il Pirata" by Bellini. With no more than a scarf for stage prop, she created an atmosphere of unbelievable tension and beauty. At 3 o'clock the following morning she and I danced the boops-a-daisy while Mickey Devron's orchestra played. She said I was the only music critic with whom she had ever done such a thing.

Constitution Hall had no more of a monopoly on the best music in town than the Kennedy Center today. Lisner Auditorium, opened after World War II, quickly became a center for matinees by the National Symphony, concerts presented by the Hayes Concert Bureau, and, despite its cramped stage facilities, the first home of the Opera Society of Washington. Lisner was the scene of the next-to-the-last concert of Lotte Lehmann, who sang there 10 days before her final concert in New York's Town Hall.

Now the Opera Society of Washington was a home-grown organization that quickly acquired a national reputation for excellence on all fronts. Begun by Day Thorpe and Paul Callaway, it profited from the imaginative services of Catholic University's James Waring, who proved as exciting a stage designer as stage director. And many of its productions were enriched by the elegant costumes of Georgetown designer Constance Mellen. Rudolf Bing, coming down to see what all the excitement was about, heard James McCracken's first Otello there, and gave Robert O'Hearn and Nathaniel Merrill their first big Met breaks because of their work in Lisner.

Paul Callaway! If I were to name one musician who made the greatest contribution to the musical life of this city in my years at The Post, it would be Callaway with no near rival. For nearly 40 years he was organist and choirmaster of Washington Cathedral. For many of those years, he was also music director of the Opera Society, conducting all the major operas of Mozart, the last two great operas of Verdi, the greatest of Monteverdi, and such diverse works as "Ariadne auf Naxos" by Strauss, "Pelle'as et Me'lisande" by Debussy, and "The Rake's Progress" by Stravinsky, with flawless taste and style.He was the conductor for the world premiere of Menotti's "The Unicorn, the Gorgon and the Manticore," and included Menotti and Barber operas in his regular repertoire.

In recent years the Washington Opera has had many conductors. None has surpassed Callaway's artistic achievements in the arena.

And all of that time he was playing the organ in the cathedral with a natural mastery few of his contemporaries could match. One of the unforgettable memories is of his first recital after four years of military duty in the South Pacific. Also in the cathedral, Callaway trained its superb choir and founded the Choral Society, of which he is still the conductor. From time to time, Callaway also conducted the Washington Chamber Singers, which he formed to perform a neglected repertoire. And in the 25 years of superb concerts at Dumbarton Oaks, he was often the conductor for evenings that featured Tourel, or the young Leontyne Price and Joan Sutherland. His musicianship is of an all-encompassing kind from which Washington has benefited immeasurably.

Over the years, press conferences for musicians varied greatly. One I shall always remember was with Artur Schnabel. Perhaps because his name lacked the glamor of some of his colleagues, I was the only person to show up. The result was a three-hour conversation in which he talked about his own 12-tone compositions, his having played "everything" written in the 19th century even though he was labeled a Beethoven specialist, and his wife's singing. He was amazed that I owned recordings of Schubert songs that he made with There se Behr, which was his wife's professional name. I suppose it was my own enjoyment of music and my interest in talking about music rather than the news trivia of the day that opened the way to the friendships that began to develop with many musicians. At a press conference for Blanche Thebom. the Cleveland mezzo finally tired of saying who designed her clothes and did her hair and said she would prefer to talk about Liszt's dramatic scene, "Joan of Arc at the Stake," which she had come to town to sing.

And then there was Sir Thomas Beecham and my proxy of his signature on the room service tab, the signature that said, "Thomas Beecham, Bart." Sir Thomas had conducted his only U.S. performance of Berlioz' "The Trojans" at Constitution Hall, Part One on Saturday night, Part Two on Sunday afternoon. Scheduled to conduct it in New York and Philadelphia, he had been unable to do so because of illness and Washington was the only city to enjoy his incomparable leadership of the great work. While there were inevitably flaws in a performance of which the late Robert Lawrence carried the rehearsals, Sir Thomas's overwhelming personality produced some supercharged playing and singing, even though in the middle of the Royal Hunt and Storm, the magnificent Britisher flung his left arm out at the chorus and shouted in the voice of a trumpet, "SING!!!!" in such a manner that the chorus suddenly sounded as if an electric prod had been applied to each individual.

The following day at noon, my phone rang. An unmistakable voice roared, "This is Sir Thomas Beecham! My dear Mr. Hume! You know perfectly well that that was NOT a great performance. If you will come for tea at 5 o'clock today I will show you exactly where and why it was not." No papal summons was ever more instantly obeyed. When I presented myself at his suite, he asked, "Would you like some 32-year-old Scotch?" Naturally I would. Whereupon, with a tone of resignation that indicated that there was no hope for these barbarian Americans, he added, "And I suppose you would like some ice! Ring for it, and sign my name."

Over the years the National Symphony, the Hayes Concert Bureau and the Opera Society increased the number of their offerings. At the same time, other important musical centers were developing. Maryland University's music department, which housed Robert Kurka's "Good Soldier Schweik" when its theater was still a green, plumbing-piped basement, grew into today's lively modern school. Robert Richman's Institute for Contemporary Arts, which once held concerts in third-floor rooms over a New York Avenue paint and wallpaper shop, moved into the Corcoran Gallery before it closed, its pioneering activities taken over by such organizations as the Theater Chamber Players, the 20th Century Consort, the Contemporary Music Forum and other, similiar groups. And the Corcoran, with its great matching quartets of Amati and Strads, became another major home of chamber music.

Washington's churches have often been scenes of some of its most important musical activity. The National Presbyterian Church, while it was still at the corner of Connecticut Avenue and N Street, was, under the leadership of the late Theodore Schaefer, one of the most vital music spots in the country. It was there that Zoltan Kodaly conducted the U.S. premiere of his haunting "Missa Brevis." There, too, Schaefer led the local premieres of such outstanding newer works as Vaughan Williams' "Shepherds of the Delectable Mountains," and the Ginastera "Lamentations." The fact that the American Guild of Organists will, for the first time, hold its biennial convention in Washington in June is a reflection of the growing importance of Washington as a center of major organ installations. The instruments in Washington Cathedral, the Shrine of the Immaculate Conception, the controversial tracker action organs in All Souls Unitarian and Chevy Chase Presbyterian, and the major organs in National City Christian and National Presbyterian Churches are only some of the factors contributing to this city's increasing influence in an essential area of the musical world.

It is a legitimate boast of Patrick Hayes that in his years as Washington's principal impresario, a term that coincides almost precisely with my own, he has brought almost every major musical figure to this city. My debt to him is thus one that cannot be paid. Among conductors whom I remember for various reasons are Herbert von Karajan, whose first words to me, in the men's bar of the Mayflower, were, "I hope to God we are not talking about music!" And Ernest Ansermet, for whom I was happy to act as chauffeur, while he explained to me why the 12-tone system COULD NOT be regarded as a viable method of composition. (He wrote a book on the subject.) And, again, Sir Thomas, who once said, following a rehearsal of the National Symphony, which he was gracious enough to conduct in Georgetown University's McDonough Gymnasium, "They tell me you conducted the orchestra there last night. Ought to do more of it. Much better way to spend your time than writing those pieces of yours." Eugene Ormandy once suggested the same thing, but I noticed that neither man offered me a guest appearance with his orchestra.

And what can I say about Walter Legge with whom I spent long hours in conversation about the whole world of music? Legge, who died not long ago, probably contributed more to my musical education that any other single person. While I did not meet him until the early '50s, he had, as the founder of the Hugo Wolf Society, the Beethoven Sonata Society, and the recording director responsible for many of the greatest recordings ever made, including those of the Philharmonia Orchestra which he founded, those of Maria Callas, whose sole guide he was, and of Elizabeth Schwarzkopf, whom he married, produced the greatest body of significent recordings of my entire acquaintance.

Where Cecil Smith, a professor at the University of Chicago, had mightily supplemented my years of study of piano, organ and voice with historical and theoretical background, Legge, through his recordings, and in our later conversations, confirmed standards of excellence that I hoped were always my guides. Three examples of Legge's ideas of perfection should be enough: He once proposed a summer festival of the late string quartets of Beethoven to be played by four musicians of a certain reputation: David Oistrakh, first violin; Igor Oistrakh, second violin; an Italian violist, regarded as the finest in the world, and for cellist, Mstislav Rostropovich. And THOSE musicians, Legge announced, would rehearse the five quartets for six weeks before playing a note in public. In another area, before Karl Bo hm even came to the preliminary rehearsals, Legge coached a cast for a recording of "Cosi fan tutte" over a period of 18 months. His singers were merely Schwarzkopf, Christa Ludwig, Alfredo Kraus and other luminaries. The final example of his standards is perhaps the simplest of all: "Before we recorded that line of the Marschallin's in the middle of the first act of 'Rosenkavalier,' where she sings 'Mein lieber Hippolyte, heute hast du mir ein altes Weib gemacht,' we tried it over at least 150 different ways." To talk about music in terms of such aspirations was to glimpse the ways in which great music is greatly made.

The years have been generously marked with peaks that have risen up to give special splendor to their surroundings. The first U.S. recital by Pierre Bernac and Francis Poulenc, at Dumbarton Oaks in 1948. The premiere of Samuel Barber's "Vanessa" at the Metropolitan--is this not the most beautiful of American operas? The premiere of Menotti's "Unicorn, Gorgon, and Manticore" at the Library of Congress, music and drama of uniquely moving expressive power. The French premiere of Poulenc's heroic "Dialogues of the Carmelites" at the Paris Opera in 1957. John LaMontaine's "Wilderness Journal," written to mark the opening of the Filene Organ in the Kennedy Center. Alberto Ginastera's "Bomarzo," a work whose genius was apparent at its premiere in Lisner Auditorium. The symphonies of Walter Piston and William Schuman. And from Leonard Bernstein so much, but especially his "Mass" marking the opening of the Kennedy Center, and his "Songfest," a celebration of this country's 200th birthday, both of them great works.

And then, of course, there was President Truman.

Through all of these years, there has been the particular growing friendship with the musicians of the National Symphony Orchestra, which is now, under the extraordinary leadership of Mstislav Rostropovich, entering a new era.

These have been years of great privilege. There is a special halo surrounding the names of two musicians whose friendship has had a unique quality: the late Pablo Casals, and the matchless Rudolf Serkin. The privilege has also been that of writing about what is for me the most beautiful of the arts in a newspaper that has cared about the growth of the arts in a city whose public has been responsive, friendly and helpfully corrective. At odd moments in recent years, I have wondered if I were a failure. This thought occurred to me when, on separate occasions, Vladimir Horowitz, Eugene Ormandy and Leonard Bernstein have all said the same thing: "But of course you are not a music critic!" Upon reflection, I think I know the generous meaning of their comment. But in spite of their expert views, I must believe that I am indeed a music critic, I hope a good one.

Meanwhile, this is no valedictory. I am simply rearranging the times and places in which I will write about, listen to, teach and love music. To all of you who have been helpful, cordial, friendly readers, my boundless appreciation.