Mixing up Beatles and classics is not an original idea any more, but the Leverett House Opera Society manages to bring it off as though they invented it.

Andy Lee's "Bach and the Beatles" is a world premiere, of sorts -- its pieces have been performed, but never before staged. "Staging" Bach cantatas and Beatle hits is not as easy as it sounds. It means keeping two dozen bodies onstage through the plotless wanderings of the Peasant Cantata looking as if they belong there, and it means dramatizing John Lennon's wonderful language without distorting it beyond recognition. And -- considering that he snuck this ambitious premiere into a House dining room -- director Ken McBain has managed something of a coup.

Bach comes first and sets the stage; the singers keep the same costumes for the Beatle cantatas, which only heightens the feeling that parts of the program's halves are completely interchangeable. The Peasant Cantata's chorus -- which actually does not sing at all -- is well handled as a pantomiming backdrop to the two singers. The drinking scenes are especially colorful.

Baritone Tom Weber, who looks more like a burgher-meister than a peasant, sings freely and clearly although without much range of emotion. Spring Fairbank sings the soprano in both cantatas smoothly and precisely. She is especially fine in the Coffee Cantata, which has a real plot, and a ridiculous one at that; Miss Fairbank milks almost as many laughs from her coffee aria as Richard Fermin does later from the Beatles. James Jones as Schlendrian has a wonderful voice, but his over-acting was almost painful by the time the cantata ended.

Those who were a little slow catching the jokes of the cantatas' German libretto have their chance for the first laugh by recognizing a stirring processional as "I Wanna Hold Your Hand." The two Beatle cantatas were both arranged by Joshua Rivkin; one became famous on the Elektra album "The Baroque Beatles Book," and the other premiered -- minus staging -- at Lincoln Center this summer. The second is a great piece of doggerel from "A Spaniard in the Works" in which Thomas Weber, as detective Shamrock Wombls, solves "The Singularge Experience of Miss Ann Duffield" and explains, "Harry Belafonte, my dear Whopper."

The chorus is perfect with extremely funny arrangements of "We Can Work it Out" and "I'll Be Back"; Weber and Fermin miraculously manage to keep straight faces and proper operatic stance through "Girl" and "Help." The orchestra, under music director John Adams, is fine with both Bach and the Beatles.

All of which only proves the old adage -- and proves it dramatically in Leverett's chandeliered and beribboned dining hall -- that what you don't have in soul you can make up for in class.