"You never know what you're going to get in these concerts," the Handel Festival Orchestra's conductor, Stephen Simon, remarked last night as he sat down to reverse roles and play an encore. What the Kennedy Center Terrace Theater audience got (and should hope to get again when the concert is repeated tonight) was Koechel 336 -- one of the tiny "Church" sonatas for organ and strings that Mozart composed to be played as an interlude between the Gospel and Epistle in the Salzburg Cathedral.

Simon had conducted the concert with Anthony Newman as organ and piano soloist, but for the Mozart Newman conducted while Simon gave a well-styled organ solo. Newman is, of course, an expert conductor as well as a world-famous performer on the organ, harpsichord and fortepiano. Last night, before accepting Simon's baton, he had given a brilliant, soulful and musically solid interpretation of Beethoven's Piano Concerto No. 2 and a delightful performance of a popular Handel organ concerto -- the one nicknamed "The Cuckoo and the Nightingale" because of the interlocked echoes of bird songs played by the organ.

The Beethoven was performed on a modern Steinway, an instrument not usually associated with Newman but one he plays (unsurprisingly) very well. It was particularly good to see this star performer, who has more than 80 records to his credit, humbly taking the role of an orchestral musician when he was not in the solo spotlight, reinforcing the bass line with his piano and unobtrusively enriching the orchestra's sound. This is no longer expected of soloists, though it would have been taken for granted in Beethoven's time, and it added a nice touch of authenticity to the performance.

Without Newman, the orchestra gave wonderfully idiomatic readings of two works that are not nearly as familiar as they should be: the Symphony in C Minor of Joseph Martin Kraus and the "Capricorn" Concerto of Samuel Barber. Kraus, an almost exact contemporary of Mozart, showed a fine talent for stormy, dramatic, deeply expressive music in this symphony. If he has written many more like it, somebody should get busy on a major revival of his music.

The Barber concerto, which sounds something like a 20th-century answer to Bach's "Brandenburg" Concertos, features three soloists on flute, oboe and trumpet exploring all possible combinations among themselves and with the orchestra. The music's textures and cadences often recall the baroque era, but there is a piquant overlay of the 20th century in the highly spiced rhythms and harmonies, and this is accentuated by the high contrast of three solo wind instruments playing against a background of orchestral strings. The music is as refreshing to hear as it is ingenious and inventive in its structures.

The solos were played by members of the orchestra (Susan Deaver, flute; Phyllis Lanini, oboe; and Dennis Edelbrock, trumpet) with the precision and flair of virtuoso soloists but the ensemble sense of people accustomed to playing together -- exactly what the music needs. The orchestra, which was excellent throughout the evening, also showed a special sense of camaraderie in this number. Even on an evening that featured Anthony Newman playing two instruments and conducting, the "Capricorn" Concerto was a highlight.