Composer Roger Ames calls his "Amarantha" a "play for singing actors," and its powerful theatrical impact gives that title some justification. But the 95-minute music drama that had its world premiere last night in the University of Maryland's Tawes Recital Hall is really an opera. The plot is based on a classic short story: "How Beautiful With Shoes," by Wilbur Daniel Steele. The music is highly expressive, instantly intelligible, flexibly varied in its styles and emotional nuances, and full of immediately enjoyable melodies -- some of them rooted in the folk idioms of Appalachia, where the story is set. Stylistically, it ranges from simple recitatives, with occasional spoken lines, up to intense and elaborate arias. "Amarantha" is a "play for singing actors," however, in two respects: The performers must generate a kind of theatrical credibility that one does not expect in "Il Trovatore" or "Das Rheingold," and they must project the English text with the kind of clarity one enjoys in the work of Sir John Gielgud or Rex Harrison. That clarity is the element on which the cast in the Maryland Opera Studio's production should work most intensively in preparing for the repeat performances on Sunday and Dec. 9. The voices were generally good and sometimes wonderful on opening night, and the acting, while variable, got its points across. But the diction grew fuzzy once the voices were raised above a certain point, in pitch or dynamics. The essence of the plot (one rich in sex and violence) got across fairly well, but the emotional high points tended to melt down into almost pure tone production. "Amarantha" is the first of three operas by living American composers that will be presented by the Maryland Opera Studio in the next two weeks, with casts that include seasoned professionals as well as student singers. The need for clear projection of English texts will predictably be equally acute in "The Love of Don Perlimplin" by Conrad Susa (Dec. 2, 8 and 10) and "The Queen and the Rebels" by Lawrence Moss (Dec. 7 and 10). Otherwise, "Amarantha" was highly enjoyable in its savagely primitive way -- a sort of American answer to "Cavalleria Rusticana," set in Depression-era Appalachia. Baritone Charles Damsel easily took top honors in the role of Humble Jewett, a desperate man, escaped from a mental institution, who is persecuted and finally killed but first experiences a moment of intense, transforming love. Susan Boykin -- as Amarantha, the woman with whom he briefly finds love -- sings with a radiant upper register that is pure tone and an expressive lower register that projects words. A fine cameo performance is given by bass Russell Wilder, a sort of Nibelung in bib overalls, and tenor Sam Savage and mezzo Joy Ratliff are excellent in supporting roles. Robert Craig, Jeff Kensmoe and Aurelius Gori have only to portray boorish ruffians, and they do so effectively. Leon Major's stage direction, unimpeded by scenery, deftly uses the whole auditorium, with a lot of action taking place in the back and in the aisles. It took a while for conductor Paulette Haupt to find the right balance of sounds, but after that her 11-piece orchestra made its statements without covering the voices. This production still needs considerable polishing, but there is a lot there to polish and it is recommended for opera-lovers with slightly adventurous tastes.