In the days since since 1980, when Riccardo Muti was appointed the Philadelphia Orchestra's music director, he has yielded to none of his fellow knights of the podium in his relish of the unconventional.

Not one of the four works on yesterday's program at the Kennedy Center -- which also opened the Philadelphia season -- could rightly be called familiar. Of them only one, the Haydn 48th Symphony in C, "Maria Theresia," has been heard here recently (under Rostropovich).

Muti's fare reminded one of selections encountered sometimes at remainder book sales -- the kind where the names of the writers are familiar but not the titles. In other words, some of the ones that got overlooked, for good reasons or not.

Along with Haydn on the Philadelphia program, there were also Weber, Prokofiev and Liszt. By far the finest work was the Haydn. It is a superbly molded, fresh and inventive product of his middle period, though its attribution to his empress is apparently spurious.

It is at its most captivating in the moments of wit and resolve that anticipate the great London symphonies. For example, there was the lethargic swagger of the minuet -- a dance movement, perhaps, but phrased by Muti with a split beat in such a laid-back manner that dancing to it seemed almost inconceivable. The sound of the reduced orchestra was sometimes a little heavy, but at no cost in clarity.

The Weber was his little-performed Second Piano Concerto in E-flat, Op. 32. It belongs to that school of piano concerto that also includes the Chopins and the Mendelssohns -- somewhere, chronologically and emotionally, between the purity of Mozart and the abandon of Schumann.

There were fine moments. In the often complex orchestration, one heard premonitions of the operas -- some sweeping octave scales, for instance, in the full strings, or the delicate chamber-size strings at the opening of the slow movement. Likewise, the piano part was full of chordal effects that pitted the instrument as a peer against the full orchestra. Malcolm Frager played the solo part with strength and grace.

If anything was missing it was in the music -- which went through many attractive motions, but never quite took sustained flight.

The next piece, Prokofiev's unjustly neglected Sinfonietta, was similarly fragmentary. It seems a transitional work -- its first movement a debonair late cousin of the "Classical" Symphony. But subsequent dance passages eloquently anticipated the bittersweet melancholy of "Romeo and Juliet."

The finale was Liszt's tone poem "Battle of the Huns," based on a mural of Attila's victory over the Romans in 451. The work is a feast of musical cliche's. Its only redeeming value is as a showpiece. And the feats of string articulation and brass sonority of the Philadelphia were so brilliant that you kept enjoying yourself -- despite the music.