Two keyboard instruments--a piano and a harpsichord--were needed for Saturday afternoon's concert in the Lyceum, Alexandria's historical museum. Both instruments were played by Christine Hagan, a musician of formidable skill on either keyboard, and the harpsichord actually got more use than the piano. That was appropriate, since the program was a part of Alexandria's 250th-birthday celebration, devoted to music that had been played in the city since its founding in 1749.

The climax of the program was the world premiere of the "Riverside" Sonata by Alexandria composer Garrison Hull--a fluent, dramatic, imaginative piano work commissioned by the city as part of its anniversary celebration. The 16-minute work, composed in modified sonata form, incorporates graceful tributes to Alexandria's history and cultural diversity, including an Appalachian tune in the Sacred Harp tradition, a Latin American lullaby and an African American folk song. This thematic material is developed with a fine sense of balance and contrasts and builds to a dramatic climax before its tranquil conclusion. Hagan, who gave a running commentary on the program, played the "Riverside" Sonata with musical intelligence and precise technique.

Earlier, on the piano, she gave a sparkling performance of the brilliant "Souvenir of Puerto Rico" by the 19th-century American virtuoso Louis Moreau Gottschalk, who included Alexandria on his concert itinerary.

The three harpsichord pieces included a Sarabande by the late Russell Woollen--a modern piece in a stately, ingeniously crafted, old-fashioned style ideally suited to an anniversary celebration. Woollen, an Alexandria composer, pianist and conductor, was for many years the National Symphony Orchestra's staff pianist and was one of Hull's teachers.

The harpsichord segment of the program opened with a short work by Georg Philipp Telemann, a German composer who was a favorite with Alexandria audiences around the time of the city's founding. It also included the elaborate, melodious overture to "The Poor Soldier," a tear-jerking ballad opera that was a favorite theatrical entertainment of the city's most distinguished resident, George Washington.