Jan DeGaetani is one of those singers who is equally at home with the modern and the medieval. She chose a middle ground, however, at the Smithsonian last night, songs of Mozart and Haydn, and proved to be a master of these as well.

Haydn wrote a number of songs on English texts, some of them settings of folk tunes. The four on last night's program presented a spectrum of moods and pretentions, all couched in a deceptively native idiom. With the fragile sound of an 18th-century piano for accompaniment, they were absolutely delightful.

By contrast, the three songs of Mozart that followed seemed even more sophisticated than they are. In these, however, some of the lovely piano passages fell victim to that instrument's unusually retiring nature.

That some of the best singers in the business don't have great voices was never more evident than in this concert. DeGaetani's voice, at this point, doesn't have much top, and a lot of the middle range lacks focus and smoothness. But she handles it with intelligence and musicality.

She knows that, in song, the words must come first, so her diction is perfection and carries with it enormous dramatic content. She knows that there must be a repertoire of many kinds of vocal sounds for the myriad feelings expressed in song, and she has at her command a great variety. Best of all, she knows the limitations of her voice and she stays within them.