The seventeenth annual edition of the Christmas Revels, now going into its second and final weekend tomorrow through Sunday at the Lisner Auditorium, may not be Washington's oldest musical celebration of the season, but it is surely the most energetic and colorful.

The participants are virtually all residents of Washington and vicinity; the Revels take place more or less simultaneously in 10 cities from coast to coast, which means they have to be essentially a grass-roots undertaking, although scripts, production ideas and technical support are provided from the national headquarters in Cambridge, Mass., where the idea originated nearly 30 years ago.

Participants, who sing, dance, act, make costumes and perform a variety of essential backstage functions, range in age from toddlers to octogenarians. They are nearly all amateurs, except for a few professionals in technical positions (lighting, stage directing, etc.). This combination has been essential to developing the Revels' unique flavor, which balances professional polish and expertise with amateur energy and enthusiasm.

In the course of an evening--just under 2 1/2 hours in this year's production, titled "The Christmas Fools"--literally hundreds of Washingtonians appear onstage. But if they wanted to, the Revels' promoters could boast of a "cast of thousands," because audience participation is an essential part of the Revels.

The program, which provides a running description of what is going on throughout the evening, prints the words and music of a number of songs, in which the audience lustily participates, sometimes after a bit of preliminary coaching.

In the performance I attended Saturday evening, I saw a few people get out of their seats spontaneously and dance in the aisles when the music (played by several local early music and brass groups) became too good to resist.

But the most spectacular audience participation came at the end of Act I. First, all the performers, massed on stage sang "Lord of the Dance" (to the tune of the Shaker hymn "Simple Gifts," which Aaron Copland used in "Appalachian Spring").

Then the audience came in, following the words and music printed in the program. Finally, the onstage singers poured out into the auditorium, took the hands of audience members and formed a long chain of revelers all holding hands and skipping through the auditorium and out into the lobby. What a way to announce the intermission!

Even trickier, in some ways, was the mass-participation performance of "The 12 Days of Christmas." The cast and audience were divided into segments and assigned to come in at specific points with their parts of the gift list (e.g., "three French hens" or "four calling birds"), and everyone harmonized on "five gold rings," producing as mighty a sound as has ever shaken the Lisner walls.

The theme of this year's revels is life in a medieval village as the end of the year approaches. Three traveling "fools" (i.e., entertainers) appear with vague astrological connections, one representing the sun (Oran Sandel), another (Mark Jaster) the moon, a third (Morgan Duncan) the stars.

They greet the village people, who are going about their daily business; they perform skits and tell stories and jokes on a portable stage, including the Hasidic tale of the three wise men of Chelm and the Muslim wit of Nasrudin the Wise.

The plot is rather loose-knit, but it provides a colorful framework for singing, dancing, children's games and, as a sort of climax, choosing and honoring a "Lord of Misrule" to preside over the seasonal celebrations. Action is nonstop, varied and kept at a high energy level.