Something exceptional happened to Vladimir Horowitz, the world's greatest pianist, on his way to a recital recently.

He was canceled.

Reasons for the action, taken by local manager James R. Robb in Philadelphia, differ.

The reason given by Robb pertains to lack of a contract signed by Horowitz. Robb said: "Anybody who allows him to play without a contract is crazy."

But the reason cited by the vice president of the Performing Arts Society, which has booked Horowitz-her name is Frances Robb and she is the president's wife-differed: "This is a business arrangement and Horowitz is not God."

That would put Horowitz in disagreement with one Robb, but in agreement with the other. He could scarcely see how playing for anyone without a contract would make someone crazy. His manager, Harold Shaw, has stated that Horowitz had been known to play first and sign a contract afterward. "That's not unusual," said Shaw, invoking a variant of the Alice in Wonderland theory of jurisprudence known as verdict first, evidence afterwards.

On the other hand, as one acquainted with Horowitz, I can say that, to the best of my knowledge, he has never been known to assert that he was now, or even has been, God-thus signifying no disagreement with Mrs. Robb.

There could, of course, be some confusion on Godhood, based on what is known to musical circles as 50 AD. This is not an updated version of Anno Domini (the Year of Our Lord) but a familiar reference to the year being celebrated by Horowitz, his family, and the Internal Revenue Service as the 50th Anniversary of his American Debut in 1928.

Complications also have been caused by the appearance of a figure resembling that of the 74-year-old pianist (most reference books give his data of birth in Kiev as Oct. 1, 1904) who has been photographed during midnight revels in a New York disco.

As there is not known to be a grand piano on the premises of the disco, no instant means of determining whether the person in question was, indeed, Horowitz existed. That gives rise to the possibility that the person who planned to give the recital in Philadelphia was not Horowitz.

The Robbs were, to be sure, in a delicate position. The gross income from the sale of 2,920 seats in Philadelphia's Academy of Music has been announced as $48,965. Inasmuch as the amount owing to the pianist has been fixed at $39,152, and the portion remaining for the Robbs was less than $10,000, a refund to the ticket buyers caused by a nonappearance of Horowitz (it has been known to happen elsewhere) could leave the Performing Art Society not merely holding the bag, but the costs of renting the hall, advertising the concert, etc.

The art of being Vladimir Horowitz thus has some factors of highly uncommon magnitude.

When, for instance, Horowitz (the musical one, not the disco-dancer) made his famous White House appearance early this year, he as characterized by President Jimmy Carter as a "national treasure." That evaluation was heard not only by the few hundred present in the East Room, but also by the millions who saw and heard the recital on national TV later in the evening.

But, according to the best sources, it was unknown then, either to Pesident Carter or to the aides who had arranged the pianist's appearance, that Horowitz had reserved the overseas rights to a videotapes of the affair. As the guest of a head of state, the Horowitz proviso was, to say the least, presumptuous.

However, together with the Carnegie Hall celebration in January of the acutal anniversary of his debut there 50 years earlier, the White House appearance got 50 AD off to a good start. The Carnegie Hall concert, with the New York Philharmonic Orchestra under the direction of Eugene Ormandy, had resulted in a recording of the Rachmaninoff Concerto No. 3. Adding the income from the video tape of the White House appearance for overseas sales could result in earnings of at least several hundred thousand dollars from the two "celebrations."

Some weeks ago, 50 AD brought an appearance, also on television, by Horowitz and the New York Philharmonic (this time under the direction of Zubin Mehta). The work was again the Rachmaninoff Concerto No. 3, providing a welcome (for RCA) reminder to the public of the Horowitz recording.

It was also sponsored by AT&T, on behalf of its subsidiaries. The Philharmonic received about $100,000 for its always needy treasury. But the earnings to Horowitz for the hour's work is believed to have been close to $400,000.

The telecast was attended by a paying audience, which may have contributed to the $55,000 Horowitz is said to have received from the Philharmonic. His fee from AT&T is attested by several sources to have been $300,000. NBC (parent company of RCA) is believed to have put in another $50,000. The arrangement also permits AT&T to repeat the telecast at some future time. Whether this is without further payment to Horowitz, I tend to doubt.

Taken together, 50 AD may be the greatest earning year in history (per performance) for any musical "name." After the Carnegie Hall appearance with Ormandy, Horowitz traveled to the West Coast for several recitals, and a program with the Los Angeles Philharmonic under Mehta's decision. That might be considered a dress rehearsal for the later AT&T telecast, because the work was, on both occasions, the Rachmaninoff No. 3.

Sebsequently-following the White House occasion-Horowitz appeared several times at Carnegie Hall in solo recitals. He also played in Philadelphia at Easter time, on behalf of the Robbs and the Performing Arts Society, a make-up appearance for two prior cancellations in 1977. Mrs. Robb contends that the Society lost $12,000 beacuse of those cancellations.

Why, then, would they return to this promotion of Horowitz in November of this year at the Academy of Music?

No doubt because, even at the division of the "take" in which the performance receives more than 80 percent of the income, a Horowitz data is a better best than Las Vegas or the stock market.

After all, he has appeared many more times than he has canceled.

When 50 AD is history, it also may be remebered for the complications that arose last March when tickets for a Horowitz recital in Carnegie Hall were announced to be available on a first-come, first-served basis. But the long line of prospective purchasers found the box office sale terminated and a "sold out" sign posted before the promised number of tickets had been bought at the window. The box office crew was subsequently "suspended" pending an assignment of blame that has not yet been forthcoming.

Is the man in the eye of the hurricane, Horowitz himself, a performer of such prodigious power that 50 AD and its attendant financial frenzies are justified? The question itself begs the true answer. I know, from any dealings with today's students, that there is only one performer they would stand in line, and pay money, to hear: Horowitz. And the same is true for an astonishing number of music lovers.

In other words, if enough people think that something is true, whether it is or not can be described as immaterial and irrelevant.

Doubtless Horowtiz plays more wrong notes now than was the case when he celebrated 25 AD with a performance of the Tchaikovsky concerto in Carnegie Hall with the New York Philharmonic Orchestra under the direction of George Szell. As suits the traditional symbolism of the years involved, every mistake now has the ring of gold rather than silver. Indeed, there wasn't even a commercial recording of the affair in 1953. The pirated one that has come into the under-the-counter market has made a lot of money for persons other than Horowitz and Szell.

Times change and so, too, do the values attached to an experience that the public chooses to consider important. It was Barnumizing when Jenny Lind was brought to this country in the mid-1800s by the famous showman: It is publicizing now that the tube has become the home showcase.

The year 50 AD has very little to do with music, but it is a case history in the art of being a "personality"-in this instance, the art of being Vladimir Horowitz.

First, you start with a gala in which attendance is reserved, at festive prices, for people who become a captive audience for a recording.

Then you accept an invitation from a head of state which, covertly, produces a valuable vieotape as a by product.

In between you make "personal appearances" (including one at Korvettes or some other discount house, as Horowitz did to promote his record), in centers hungering for such a visitation.

Finally, you accept a television engagement, with orchestra, performing the same thing of which you have previously made a recording, blanketing all the parts of the country unreachable in personal appearances.

For some who might raise the classic question: What can you do for an encore, the counter-question can only be: Who needs it?