Everybody knows that Vladimir Horowitz was (a) a great musician, and (b) a temperamental human being. He was different from his father-in-law, Arturo Toscanini, (I gather; I did not know Toscanini, though I worshiped him) in that he could be surprisingly affable, even unpredictably so. I met him under the most unexpected circumstances: on the Eastern Shuttle coming up from Washington 15 years ago. He came over and introduced himself and his wife, smiles lighting up the whole of his volatile countenance. For a while we were friends. I remember especially an evening at his home in Connecticut when another guest and I conspired (ahead of time, over the telephone) to devise ways to bring him to the keyboard. I mean, why have supper with perhaps the greatest pianist in the world and not get him to play for you? What, I asked him, would be his program the following month, when he would appear at the Metropolitan Opera House as the first one-man performer in the history of the house? Well, he said, maybe begin with something by Scarlatti. Then perhaps a sonata by Clementi -- I grabbed my cue and gave the eye to my co-conspirator. ''Clementi? You are going to waste your time with Clementi?'' ''Why Clementi?'' my friend, his brows furrowed, chimed in provocatively. We earned the national actors' award, because if we had rehearsed it, it could not have gone better: Vladimir Horowitz rose. His voice and countenance were now grave. ''You doan lahk Clementi? Clementi wass a JEE-nee-us! Clementi is as goot as the middle Beethoven!'' ''Come on,'' I said condescendingly, pushing my luck. And he marched to the piano, lifted the lid -- and we heard not only Clementi, but the entire historic two-hour concert he was to give two weeks later. He and his wife were redoing the living room in their country house at the time and there was a third guest, their interior decorator, who during an interval while our host was walking his cat and our hostess was off in the kitchen somewhere, confided to us in whispers the great happening of the week before, when the local Italian curtain-maker had come in to quote the cost of the new set of curtains. ''It will come to $278,'' he said to the decorator. Pause. ''Or -- for nothing! If Mr. Horowitz will play next Sunday for me and my wife.'' This was on the order of suggesting in the presence of Cleopatra that, rather than pay to repair her gondola, she might extend her favors to the shipwright. Horowitz froze, and there was a moment of most awful tension. Horowitz then stood up, bowed his head slightly and said: ''I would be honored to play for you and your wife on Sunday.'' This was noblesse oblige in marble. It would be either that -- Horowitz would accept the alternative -- or else Horowitz would pull out a shotgun and end two careers, one musical, the other having to do with curtains. He was also a man of considerable polemical shrewdness. Mike Wallace and his cameras were at Horowitz's New York apartment doing a ''60 Minutes'' segment, and Wallace graveled out in his interrogatory-accusatory voice, ''Is it true that for 13 years you stayed here without going out?'' Horowitz looked at Mike Wallace, the disappointment of a child on his face. ''Vot? Vot you mean? You doan like my room here?'' The camera did a little tour of the comfortable living room. ''Vot you doan like about my room?'' Poor Mike. What can you say to someone who suggests that questioning his self-enclosure in an apartment for 13 years is the equivalent of finding his living room unattractive? Ah, but the time came when the Maestro wrote me off, wrote me off without a cent. The circumstances were: another invitation by Horowitz to dinner, which we accepted. After dinner, the Great Man disappeared to walk his cat, or whatever. It had been a most awfully long day, and after a half-hour or so I beckoned to my wife, rose and bade goodnight to Mrs. Horowitz, who was clearly startled at guests leaving before they were invited to do so. He was a stickler for decorum. Once he showed me a letter from the first lady, the first sentence of which had shocked him. ''Jimmy and I are so pleased that you are coming to play for us at the White House on ... '' The date followed, and the time. ''Imagine! She sess 'Jee-mee' when she mean zee pressident off the United States! And she says nothink -- NOTHINK! -- about Wanda comink with me to the White House!'' I clucked my grave Republican shock at Jacksonian manners. I never heard from him (or her) again. He was a very great musician, and as long as music is bought and sold, presidents of the United States and curtain-hangers in Ridgefield, Conn., will ask for ''the Horowitz recording.''