For 11 years, the husband-and-wife team of pianist William Bolcom and mezzo-soprano Joan Morris have been performing American popular songs ranging from the late 19th century to efforts by Leiber and Stoller. Last night at The Barns of Wolf Trap, the duo presented a show billed as "The Fourth 'B': Irving Berlin." Were the equivalent to a Mount Rushmore for international musicians constructed tomorrow, Berlin would certainly deserve a place alongside J.S. Bach, Beethoven and Brahms.

In the course of 27 selections, Bolcom and Morris reaffirmed (as if it were necessary) that Berlin is the greatest American songwriter, especially in his ability to capture the Zeitgeist of our culture. With a background in acting and singing, Morris brought a marvelous interpretive quality, variously dramatizing the fey wit of "At the Devil's Ball" and "Not for All the Rice in China" while investing the poignant blues, "Supper Time," originally sung by Ethel Waters in the revue, "As Thousands Cheer," with heartfelt feeling.

For his part, Bolcom supplied perfect accompaniment throughout, subtly injecting bits of humor, in the form of prominent bell-like trills in "White Christmas," and generally understating chordal embellishments. Visually, he was the perfect foil to the animated, at times hammy antics of Morris.

The performance is repeated tonight.