In 1778 when Mozart wrote the theme and variations that begin his piano sonata, K. 331, he could not have imagined the harmonic lengths and contrapuntal complexity they would inspire over a century later in Max Reger. However, from the evidence of well over a dozen sets of variations Mozart wrote on other composers' themes, we know that he thoroughly approved of the process.

Last night Rafael Fruhbeck de Burgos opened his program as guest conductor of the Philadelphia Orchestra with a performance of Reger's probing variations and fugue on the familiar theme and made it an experience of rarest beauty.

Let's admit at the outset that Reger's music is indeed "the food of love." And Reger, having given excess of this food, surfeits the listener, so that the appetite may, indeed, sicken and so die. If this be true, what a heavenly way to go!

There have been those in the past who, unknowing, have said Reger lacked restraint or inspiration. Fruthbeck de Burgos proved last night that what Reger needs is a great orchestra and a conductor of special insights.

With the Philadelphia Orchestra an ideal means for carrying out his conception, he conducted with immaculate but deeply impassioned feeling, letting an impeccable taste broaden phrases, make ritards, and amplify the sweetest rapture of the music. No other way could produce the glorious sounds that poured from the Kennedy Center stage last night.

Every note of the variations and fugue proceed directly out of Mozart's theme. But as the variations proceed, Reger discloses realms of thought that could only come after Wagner had lived to create a new musical world. The eighth variation is one of the most profound moments in all music. Last night the conductor and orchestra brought it fully to luminous reality.

Rimsky - Korsakov's Scheherezade came after the intermission, another work for which this orchestra has always seemed predestined. Norman Carol's elegant perfection of style introduced the glories of the Philadelphians' soloists, harp, clarinet, horn, oboe, flute, all in handsome array. But the crown of the evening was the transforming power of the Reger.