Among the many benefits Leonard Slatkin has brought to the National Symphony Orchestra, the most notable can be heard in the music of Beethoven. There could hardly be a more convincing demonstration of this fact than Saturday night's program at Wolf Trap: the "Leonore" Overture No. 3 and the Ninth Symphony. And the demonstration could hardly have been given under more challenging circumstances.

Besides the usual problems of an outdoor performance on a hot, humid evening, Saturday night had a thunderstorm playing along during part of the program. There was an interesting (and rather theatrical) thematic touch in the rumble of distant thunder just before the first downbeat of the symphony, but the synchronization later was not very precise. Fortunately, after stepping on a pianissimo passage in the second movement, the thunder wandered away for the rest of the evening. The orchestra retuned before the third movement (the heat and humidity made that advisable), and the last two movements then turned out to be the best part of the evening--thanks mostly to Beethoven but also, in no small measure, to Slatkin and his performers.

Drama is an essential ingredient in both compositions, and Slatkin brought it out clearly with carefully calculated contrasts of tempo and dynamics. The orchestra responded with the usual precision of ensemble and nuance that it musters under Slatkin's baton, and the Cathedral Choral Society brought brilliance and power to the symphony's stunning finale.

The vocal soloists sang superbly: bass-baritone Richard Bernstein and tenor Richard Clement in spotlighted passages, soprano Camellia Johnson and mezzo-soprano Mary Ann McCormick in music that was at least as challenging though less conspicuous.