The man running around the stage, brandishing a wicked black mustache and an enormous battle-ax is Ko-Ko-Ri-Ko, whose name sounds Chinese (or vaguely Oriental) but is also what French roosters say instead of "cook-a-doodle-doo." He snarls gloriously, plots insidiously, and when he is not waving his ax he is likely to be beating on a large gong or a big bass drum.

He also sings, in French and Italian, with a quality that seems surprising when you look at the audience of small children and parents, but not when you learn that under the mustache is William Read, a baritone who has sung often in Washington and whose other credits stretch from the Israel National Opera to the Metropolitan.

He is singing at Wolf Trap's Little Theatre in the Woods this summer as the villain in the Children's Opera Theater production of "Ba-Ta-Clan," a Jacques Offenbach opus that is a little like Gilbert and Sullivan and (in this staging, which is Washington's) a bit like Saturday-morning television. Besides four excellent singers - the others are tenors Michael Sparacino and Philip Smith and the spectacularly good soprano, Myra Merritt - "Ba-Ta-Clan" offers its young audiences some frenzied stage action, bright Offenbachian tunes, lots of balloons floating away at the grand climax and a big bass drum, placed in a corner of the stage where the most intrepid kids can give it a whack on their way out.

For nearly an hour each Saturday morning this summer, "Ba-Ta-Clan" is keeping hundreds of children absorbed in opera. It is not an opera in the class of "Tristan" or "Rigoletto" which might set some of the 4-year-olds squirming in their seats, but it is over a century old, it is sung in French (with a bit of Italian and quite a few nonsense syllables) and besides the Paris cabaret flavor of its composer's basic style, the music has echoes of Bellini's "I Puritani" and Meyerbeer's "Les Huguenos."

Out under the trees at Wolf Trap, the atmosphere of the Little Theater is something like a summer camp - very rustic, with long wooden beches where the kids sit not very quietly until the story begins, the magic takes hold and they start to wonder why those people are chasing one another around the stage. The plot is as complicated as it is silly; there are rumbles of revolution and a struggle for the throne of a vaguely Chinese kingdom, and most of the opera's characters turn out to be Frenchmen passing for natives (a real challenge, since they don't speak the language.) But everything is made clear (well, relatively clear) with the aid of an English-language narration.

During the arias, the members of the chorus dance off and on carrying a translation of the words painted on giant cue cards like comic-strip balloons. Some of these are relatively straightforward ("Alfred, all is over" and "I fear our death is near" in one duet), but there are also editorial comments: "Offenbach is just putting us on" ane "If we translate this we'll get busted."

Near the endof the show, while the dread call to revolution, the "Ba-Ta-Clan," is being sung, the chorus stages a small demonstration with its dialogue balloons: one bears a picture of a clenched fist, another urges "More Jobs for Artists" and a third says simply, "Hail to Joan of Art," a tribute to Joan Mondale, one the project's supporters.

"More jobs for artists" is one of the things that Children's Opera Theater is all about. Established two years ago, it received a grant of over $160,000 this year from Montgomery County under the CETA (Comprehensive Education and Training Act) to provide employment and experience for artists and technicians who are building professional careers. While doing that, it has also exposed more than 50,000 children to live opera in schools and other auditoriums during the academic year and at Wolf Trap's Little Theater in the Woods during the summer.

Performances will be given at 11 a.m. each Saturday through August. For reservations call (703) 281-5587.