Mozart's genius resided in his ability to express musical ideas gloriously in a vocabulary of details. Gerard Schwarz, who is the conductor of the Mostly Mozart Festival Orchestra and who is presiding over three of this year's Mostly Mozart Festival concerts at the Kennedy Center Concert Hall, is a man of action rather than details. He seems most comfortable urging his small orchestra to unflagging momentum through thickets of musical business. This makes for excitement, but not necessarily for great Mozart.

It is not surprising, therefore, that the orchestra sounded most focused and graceful last night when Schwarz finally turned his attention to details, in the andante of the Mozart Symphony No. 20 in D Major (K. 133). Mozart was 16 when he wrote this symphony, and the musical idiom itself was still an issue for him. Thus the andante seems almost a stylistic caricature, and Schwarz carried it off beautifully, with a leisurely pace and a lovely sense of shape.

For a second night, the program featured two soloists, one very young and one very experienced, but this time it was the differences that were striking.

Pianist Rudolf Firkusny is an old hand at the concert business and he approached the Mozart D Major Concerto No. 16 (K. 451) with an assured matter-of-factness that was both reassuring and pleasant, if not particularly enlightening. He has a way of beginning lines with momentum already established that lends an effortless impetus to each phrase, and his playing was both exceptionally clean and weightless.

On the other hand there was nothing matter-of-fact about the way cellist Matt Haimovitz dug into the Boccherini B-flat Concerto. At 15, Haimovitz already has an impressive history of performances, and it is clear that, at the moment, he is into gesture. He gave a fervent account of the outer movements, moving with a touch of impatience from one phrase to the next. The middle movement, however, provided a glimpse of what may lie ahead for this young man. Here the music had real warmth, rather than just heat. Lines were seamless and moved as if of their own accord. Let's all hope that Haimovitz continues to develop this aspect of his artistry.

Haimovitz explored more of the repertoire in the preconcert concert, teaming with pianist Anne-Marie McDermott for performances of the Debussy Cello Sonata and Paganini's Fantasy on Rossini's "Moses in Egypt." Here, without the tempering influence of Schwarz's baton, tempos got faster than they should have, but the Paganini sang with a fine sense of line and a gorgeous tone.

McDermott opened the concert, with a boldly outlined performance of the Bach A Minor English Suite. She has a strong left hand that sometimes dominated the texture, but, particularly in the soft movements, she found a splendid balance and evenness of touch.