Christopher Hogwood brought his Orchestra of Original Instruments to the Kennedy Center for an unusual concert Sunday night. This group of New Yorkers playing 18th-century instruments was organized in 1984 for the Mostly Mozart Festival in New York and is now reincarnated each summer for concerts in several cities.

In its first Washington appearance, it sounded considerably less polished than Hogwood's primary orchestra, the Academy of Ancient Music, but there was charm and no doubt authenticity in the slightly rough edge heard in some of its ensemble playing. There was also a lot of energy and excitement.

Besides using gut strings and valveless horns, Hogwood tried to put a period flavor into the arrangement of the music. He began with Mozart's "Posthorn" Serenade (producing the roughest ensemble sound of the evening), but interrupted it halfway through, as Mozart himself might have done, with Giovanni Battista Viotti's Violin Concerto No. 13 in A. To a modern audience, it seemed odd, as well as very long: four movements of "Posthorn," followed by a slight pause, then three movements of Viotti, a lot of applause and bowing, then three more movements of "Posthorn." But the string sound of Viotti did provide a welcome contrast to the prevailing wind tone in Mozart's serenade.

The second part of the concert, only half as long as the first, featured fortepianist Steven Lubin in Beethoven's Piano Concerto No. 1, preceded by his variations on "Rule Britannia." Lubin conveyed a sense of improvisation, both in the variations and in his own elaborate first-movement cadenza for the concerto -- which drew laughter from the audience when it threw in a reference to "Rule Britannia." Unlike modern virtuosos, but like the soloist in Beethoven's time (who would have been Beethoven himself), Lubin played along in some loud tutti passages, not as a soloist but as a member of the orchestra. But when he needed to stand out as a soloist, he did so splendidly.