The identity of the pianist (listed on the program simply as "Armenta") was a mystery to most of the audience last night at the University of Maryland Piano Festival.

The program was hardly enigmatic but enormously challenging, consisting of two massive sets of variations. The evening opened with Brahms' brilliant Op. 24, Variations and Fugue on a Theme by Handel. It concluded with one of the few works that would not be anticlimactic after that stormy, delicate masterpiece: Bach's kaleidoscopic "Goldberg" Variations. Clearly, Armenta, whoever she was, intended to make a major statement in her Washington debut.

Born Armenta Adams, the pianist was a child prodigy who began to study at the New England Conservatory when she was 4 and later went through Juilliard on scholarship and competition prizes. About 10 years ago, after the birth of twins, she retired to devote full time to her husband and four sons. She performed only occasionally around her home towns (first in Georgia and later in North Carolina), but she brought into her retirement rave reviews from Stockholm, Brussels, Amsterdam and New York.

Now, with her family fairly well grown, Armenta is ready to return to the national and international concert stage. Or almost ready. Last night's performance was somewhat uneven, and she may need a few more appearances to get back into top form. But the best moments in the program revealed a distinctive musical personality with the temperament and technique to put her individual stamp on her repertoire.

There were many moments of sheer magic: in the Brahms, for example, the abrupt contrast between the hard-hitting Variation 4 and the dreamily romantic 5, the metrical subtleties in 9 and the phrasing of 21, which was soft and expressive as required but also superbly profiled. On the other hand, 14 lacked sufficient definition, the chord sequences in 20 were not as soft or legato as required, and the final fugue would have benefited from more clarity.

The "Goldbergs" began with a daringly slow but beautifully phrased and ornamented statement of the thematic melody, and Armenta's style was deftly varied to meet (or define) the music's many rapidly changing moods. Her counterpoint had more clarity here than in the Brahms fugue, and occasional shortcomings (for example, the need for more pointed phrasing in the fifth and sixth measures of Variation 7) were small and momentary.

Armenta is a significant talent who should polish her dormant skills with more frequent exposure to discerning audiences.