Leonard Bernstein likes to mess around, which is one reason he is such an interesting conductor.

His version of Beethoven's 6th Symphony, which the Vienna Phiharmonic played with such relish at the Kennedy Center Concert Hall last night, is painted in the contrasts of a silhouette rather than a photograph. His slow movement moved like slow motion, every detail etched sharply, inner voices starkly revealed and the timbres of the orchestral choirs in sharp contrast to each other.

Perhaps this was calculated to be a foil to the Wagner that followed, well-integrated excerpts from Act II of "Tristan and Isolde." Here he roused himself and the orchestra to waves of dramatic passion, whipping every ounce of power from the long phrases, and leaping into the air when mere beating proved inadequate.

As Isolde, Gwyneth Jones easily made herself heard over the orchestra, sharping on the loud passionate passages but singing with accuracy, if with evident carefulness, on the rest.

Jess Thomas sang a pleasant, middle-of-the-road Tristan, pacing himself well but never really committing himself to the drama.

The evening's loveliest singing came in the all too brief lines allotted to Nancy Williams as Brangane. From the back corner of the stage (clearly a discreet distance from the lovers) her voice floated out over the orchestra with beauty and authority.