The program Paul Hillier conducted Sunday at the University of Maryland's Clarice Smith Performing Arts Center was full of surprises and striking contrasts. More important, like all musical activities in which Hillier is involved, it was intelligently prepared and polished to a high gloss. He is one of the most important choral directors of our time, and the 12-voice a cappella Danish chorus Ars Nova upheld the reputation he has built with the Hilliard Ensemble and the Theatre of Voices. Like much of his work, the performance presented, perfectly, music that is seldom heard and eminently worth hearing.

This fascinating program was sung with transparent balances, harmonies in precise intonation and an expressive range as wide as the material, composed five centuries apart. It included modern music by Scandinavian composers and 16th-century music by English and Flemish composers: William Byrd and the less familiar Giaches de Wert and Jacob Obrecht.

The singers were totally at ease in the smooth, mellifluous polyphony of the old masters, which opened the program, and in the "Dominus regit me" of Carl Nielsen, dating from 1929 but in a style indebted to Renaissance music.

Then came the surprises and contrasts. First was 1980's "Wie ein Kind" ("Like a Child"), by Per Nørgård, in which a lullaby (sung with nonsense syllables) morphs into a funeral march. There were cries, incantations, vocal glissandi and a contrasting, bucolic second movement. It was followed by Pelle Gudmundsen-Holmgreen's "Three Stages", a new work commissioned by Ars Nova, which samples Luciano Berio in a first movement based on street cries of 17th-century London, and Clement Janequin (c. 1485-1558) in the second movement, which bubbles over with imitations of bird song. The contrasting images (bustling urban life and deep, tranquil forests) are curiously synthesized in the third movement.

Less experimental music by Sven-David Sandström, Bent Sørensen and Arvo Pärt agreeably filled out the second half.