For while Sunday night, you would have sworn the Kennedy Center Concert Hall was flooded with laughing gas.

The Washington Bach Consort Chorus was zinging out "Ho! Ho! Ho!" in flawless counterpoint from all over the stage; conductor Stephen Simon, grinning from ear to ear, was performing what looked like an aerobic dancing exercise on the podium. The violins of the Bach Festival Orchestra were producing a sound remarkably like hysterical laughter, and even the audience for Handel's "L'Allegro, il Pensieroso ed il Moderato" seemed ready to start rolling on the floor.

All this hilarity was provoked by a single syllable ("ho," naturally) that Handel found in a line about Laughter, an allegorical figure invented by John Milton, "holding both his sides." Tenor Rockwell Blake, the best singer in an evening of generally fine singing, was the first to break out with the "ho-ho-ho-ho-holding," line, but it soon spread to the chorus and to everyone in the place. It seems impossible not be be happy while singing, playing or even listening to this music.

The "laughing chorus" was only one picturesque element in more than two hours of colorful music. No composer has ever surpassed Handel in the ability to paint musical pictures, and Milton's two poems -- packed tight with tiny, vivid, rapidly shifting scenes -- provided him an unparalleled opportunity. A mention of a nightingale in the text inspired an elaborate flute solo played dazzlingly by Alice Weinreb; a reference to "the hounds and horn" drew a magnificent horn solo from Laurel Ohlson; trumpets and timpani, the cello, the organ and even a little carillon gave vivid color to the music.

*In this brilliant setting, "L'Allegro" (the happy man) and "Il Pensieroso" (the pensive man) might almost have been translated "The Manic" and "The Depressive." An added segment (not by Milton) resolved the debate between these states of mind with a plea for moderation -- demonstrating, as we might have suspected, that moderation is duller than the extremes, at least for purposes of vocal music. Fortunately, it was brief.

The orchestra and chorus were superb under Simon's vivid direction. Bass-baritone Michael Devlin and (after a bit of warming up) mezzo Katherine Ciesinski gave excellent performances. Judith Blegen suffered intermittent problems in her upper register but sang with her usual intelligent musicianship.