THEY didn't have vaudeville back in the Middle Ages -- perhaps because the good people tended to spend their time erecting cathedrals instead of theaters. But if there had been a Roxy at Coventry or a Loew's at Chartres, the Folger Theatre's newest show, "A Medieval Christmas Pageant," would have been a natural to tour the circuit.

Pooling their resources with The Folger Consort, the company has put together a bill of songs and playlets, jigs and liturgy that, for all the underlying seriousness of the event it celebrates, still has a lot of the flavor of the old three-a-day. Like most bills, some of the acts are better than others and in one instance or two, you may find yourself wishing for the hook -- or the medieval equivalent. But for the most part, this is an evening of sweet and charming Christmas pleasures that will do far more to put you in the requisite spirit than Ford's ersatz "Christmas Carol."

At the Folger, things begin with a slice of backstage bustle. The actors are limbering up, the musicians are tuning their instruments. A juggler saunters on and off again, honing his skills. Props and scenery are rushed into place; costumes checked and little confidences exchanged on the run. In fact, I half-expected the performers to burst into a chorus of "Another Opening, Another Show."

Instead, they sing "Stella Nuova," "Gloria'n cielo e pace'n terra," and a 13th century "Musick Drama," entitled "The Shepherds." The drama in the latter is not overpowering -- an angel announces the birth of Christ to the three shepherds, who encounter a pair of midwives on their way to Bethlehem. But in the brief Latin exchanges lie the seeds of theater, which had pretty much lain dormant since the collapse of the Roman Empire. Director Ross Allen stages the piece with a formal grace that makes it more than just a historical oddity.

As it moved out of the church and into the marketplace, the medieval theater acquired a lustiness and vigor calculated to please the rowdy populace. By the time of "The Second Shepherd's Play," which forms the crux of the Folger's pageant, once-pious shepherds were moaning about the cold weather, their empty stomachs, the idle rich and the ever-present threat of scoundrels making off with their sheep.

Mak (John Wojda) is the scoundrel-in-chief here, although his wife Gil (Mikel Lambert, her eyes as wonderfully wide-eyed as the lies on her lips are blatant) runs him a close second. The play is nothing more than a protracted bit of chicanery: Gil and Mak's attempts to pass off a stolen sheep as their newborn babe. But the deception is a lively one and Craig Paul Wroe, with the considerable assistance of costumer Bary Odom, is rather adorable as the lamb in swaddling clothes. Unfortunately, Wojda is one of those actors who tries to be everywhere at the same time and his comic sloppiness mitigates some, if not all, of the fun.

The Folger players really shine, however, in "The Mayor's Christmas Pie," a farcical romp they have developed from a traditional tale about a rotund baker who gets done out of a meat pie and a Christmas tart (and quite possibly his wife's favors) by a pair of canny beggars. Director Allen has inflated the tale to cartoon dimensions, and the cast (Jim Beard, Chris Casady, Thomas Schall and Floyd King) acts it with grand improvisational zest. King, who has both an astoundingly rubbery face and the discipline not to overstretch it, is a decided improvement over the Folger's usual clowns.

Between skits, the members of The Folger Consort, dressed in red and green and looking a bit like elves under a tree, provide holiday music of solemn and sprightly strains. (See accompanying review.) While they're fiddling their fiddles and piping their pipes, you'll notice the actors sneaking on for a listen. Some of them nod along with the music. Others allow themselves to kick up their heels in the background or waft a chiffon scarf into the air. It is this sense of overlapping pleasures, of gentle camaraderie, that is responsible for the aura of goodwill that hovers over the Folger stage.

"A Christmas Pageant" may be a little bit of this and a little bit of that, some of it arcane, some decidedly plebeian. But it all springs from a sense of the occasion. And the vaudeville format, far from being irreverent, adds a touching dimension. Rich men give rich gifts at Christmas. Painters paint splendiferous frescoes. Kings build cathedrals. And performers? Why, they perform.

A MEDIEVAL CHRISTMAS PAGEANT. Directed by Ross Allen; sets, Hugh McKay; lighting, Richard Winkler; costumes, Bary Odom; choreography, Virginia Freeman. With John Wojda, Jim Beard, Chris Casady, Thomas Schall, Floyd King, David DiGiannantonio, Paul Norwood, Mikel Lambert, Craig Paul Wroe, and the members of The Folger Consort. At the Folger Theatre through Jan. 9.