THE WIZ -- National Theater, 1321 E Street NW. Reservations, 628-3393.

The stage production of "The Wiz," which opened an extended return engagement in Washington this week, is a marvel of rather ordinary elements that somehow add up to a grand total.

There is no stunning performance nor any particularly memorable tune, yet the show is as witty, powerful and compelling as any black musical since "Porgy and Bess."

Not the least of the joys the production brings us is that it washes away the bad taste left by the movie "Wiz," a misbegotten star turn that preached itself to death.

On stage at the National Theater, "The Wiz" whizzes along from curtain to curtain with hardly a pause except for applause, which the performers milk but thoroughly deserve. The one real show-stopper is a solo by Kamal (Kenneth Scott) as The Wiz himself, which rises to a finish of truly operatic quality.

Kamal's brilliant handling of the one big vocal chance the score gives him makes one wish the other members of the superb company had been given similar shots. The two songs in the show that have the potential to be hand-clappers and toe-tappers, "Get on Down" and "Bad News," come off curiously formless, almost slurred.

But the score is at least adequate; the single element of the production that failed on opening night was the sould system. Why it was decided to put radiomicrophones on the principal peformers is unclear, because the acoustics at the National are such that any professional player should be able to project to Pennsylvania Avenue.

The sound issued from loudspeakers on each side of the stafe, giving a point source that seemed the same wherever the performers might be onstage. It is hard to maintain the willing suspension of disbelief when Dorothy (Renee Harris) skips to the other side of the stage and leaves her voice behind.

Presumably this will be corrected, since it is a simple technical problem, but it would be better yet just to forget the electronics.

And for that matter, forget the quibbles. Performers Harris, Kamal, Vivian Bonnell (Addaperle), Charles Valentino (Scarecrow), Clyde Jacques-Barrett (Tin Man), Ron Taylor (Lion), Carolyn Miller (Evillene) and Tina Fabrik (Glinda) are not only outstanding in their roles but so supportive of each other that they consistently keep the quality of the production better than the already high level of their material. Some theatrical companies have such magic they could carry anything, and one comes away from this sparkling "Wiz" with the feeling that L. Frank Baum, author of "The Wonderful Wizard of Oz," is beaming down on them from Hack Heaven.

Harris's interpretation of Dorothy is a bold one, and there probably are few performers who could get away with it. Her Dorothy is so young and such a cutiepie that the she almost -- but never quite -- simpers; and whenever her lines begin to verge on the treacly the art and force of her traveling companions come to the rescue.

and the dancers. You probably could count them on your fingers if they ever slowed down, but they move with such energy and grace and change costumes so fast that if the credits didn't give George Faison as the choreographer you would think it was Busby Berkeley.

"The Wiz" is... wizard.