As an evening of musical pleasure, Saturday's Mostly Mozart Festival concert at the Kennedy Center was a delight, if a trifle long. As a sampling of the orchestral works of Haydn and Mozart, however, it was weighted heavily in Mozart's favor. Were there a Mozart underground operating whose purpose was to exalt Mozart while discrediting Haydn, more damning comparisons than the Haydn Symphony No. 7 ("Le Midi") with the Mozart Symphony No. 36 ("Linz"), and the Haydn C-Major Cello Concerto with Mozart's A-Major Piano Concerto, K. 488, could scarcely have been found.

Here was Mozart at his most sophisticated and polished, at the peak of maturity and secure in the structures he manipulated with such ease. And here was Haydn early in his career, still experimenting. The Seventh Symphony still retains a harpsichord as its backbone. There are elements here of the Baroque concerto grosso, and some of the instrumentation, such as the use of the bass viol as soloist in the third-movement Trio, is not the artistic decision of a mature composer. Fortunately, Haydn's reputation does not rest on these two works alone.

Pianist Bella Davidovich approached the Mozart concerto with a sense of purpose that, at times, seemed to impose her will on the music. The second-movement Adagio was lovely, thoughtful and beautifully shaped and free of the facile quality of the outer two movements. Conductor John Nelson found a fine balance of orchestral sound and seemed musically and emotionally attuned to Davidovich's artistry.

Cellist Lynn Harrell danced through the virtuosic Haydn concerto with splendid orchestral support and earned bravos from the audience for his effort.

The preconcert recital found Davidovich and Harrell not always in agreement about the character of the Chopin Cello Sonata. Davidovich emphasized the clarity and the shape of the lines, while Harrell seemed to be carried away by their breadth and color. Of the two, Davidovich made the most sense.