MAGGIE MAGALITA by Wendy Kesselman; directed by Wallace Chappell; costumes by Ken Holamon; sets and lighting by Charles H. Vaughan III.

With trini Alvarado, Ruth Rivera, Teresa Yenque, John L. Bucek, Jane Jenny Fontanez and Alina Arenal.

At the Terrace Theater (on an irregular schedule) through April 19. Some tickets are available for Saturday's public performances at the Friends of the Kennedy Center desk.

Lost ethnicity may not be the most sensational or original subject matter these days, but "Maggie Magalita," the prize-winning children's play of the 1980 National Children's Arts Festival, turns out to be a reasonably lively -- if crudely constructed -- discourse on that theme.

Maggie is a New York teen-ager who has lost almost all traces of her (unspecified) Latin American origins. When her elderly grandmother arrives in the United States, Maggie wages an ill-tempered rebellion against her role as escort and pet granddaughter -- and against her diminutive Spanish name, "Magalita."

Reluctantly, she takes her grandmother to a department store, but when the old woman balks at using the escalator, Maggie almost pushes her onto it. As the play progresses, however, Maggie gradually discovers unexpected things about her grandmother -- she plays a mean game of dominoes, for example -- and sheds some of her own defensiveness about her immigrant origins in the process.

Under Wallace Chappell's direction, "Maggie Magalita" is smartly acted -- particularly by Trini Alvarado (of the movie "Rich Kids" and the play "runaways") as Maggie, and by Peruvianborn Teresa Yenque as Abuela, the grandmother. At the ripe old age of 13, however, Alvarado may be a little young for the exclusive, above-the-title billing she gets in the program. Ah, stardom!) Charles H. Vaughan III has designed an ambitious set that adds to the production's effectiveness.

Unfortunately, the play itself, by New Yorker Wendy Kesselman, has rather more redeeming social value than basic dramatic stength. A number of scenes are so brief and mild they might as well not be there. Maggie's whole conversion from intolerant brat to reverent granddaughter is conspicuously unmotivated, and will probably leave even very young theatergoers feelings, at least subconsciously, that they have been had.

Nevertheless, since a good deal of "Maggie Magalita" transpires in Spanish, Spanish-speaking or Spanish-studying youngsters should find it an enjoyable excursion.