"Joy, A Musical Tribute to Duke Ellington," the newly commissioned stage work that opens to the public tonight in the Kennedy Center's National Children's Art Festival brings to this event something that seldom brightens such occasions-star quality.

Singer Leon Bibb has put together 50 minutes of song, dance, jazz instrumentals and succinct commentary that goes far beyond its assigned task of introducing the bare roots of jazz to teen-age audiences.

If one is hungry for good jazz, and lots of people are in this city where it is in short supply, one should not be put off by the fact that Bibb and his colleagues have come here with a "children's" label. This polished presentation will be repeated for the public Thursday, and during the next few days for invited high-school audiences.

The commentary is minimal-instructive rather than pedantic-and this small revue teaches jazz mainly by example. From a mention of the influence of chain-gang songs on jazz, Bibb launches into a march around the stage of the Center's Terrace Theater singing a nameless chain-gang song picked up years ago for the Library of Congress' Lomax collection from an old prisoner at the Sugarland, Tex., prison.

Ellington gets his due at other times, particularly with Lovie Eli in "I'm Going to Live What I Sing About;" by the whole company in "Jump for Joy," and in a medley with the Northwest Jazz Sextet and dancer Terri Griffin.

Also on tonight's program is "The World of Folk Tales," a presentation by the Umbrella Players of Atlanta of close to a dozen stories through mime, choreography and narrative. They range from Aesop's "The Eagle and the Turtle," with the actor playing the eagle in a daredevil pilot's helmet and goggles, to a West African tale, "The Frog and the Moon," in which the accompanist puts down her cello and makes guttural frog noises. This is ingenious material for an elementary school audience.

The other main presentation of this first of the festival's two weeks was a mini-opera, Seymour Barab's "The Toy Shop," which is designed to introduce children to the conventions of opera/arias, duets, and a rousing ensemble conclusion.

**barab's music is simple and lyrical, if not profound. And the work presented by the New York City Opera Theater achieved its goal far more sucessfully than most new operas for adults performed here lately.