What are skatches? The simple program listing, Saturday afternoon at the Library of Congress, gave no information except the name of the new composition by Paul Bogatko, a 40-year-old American composer. But once the music began, the definition became obvious: skatches are musical sketches that include scatting -- a key ingredient of the now-classic musical genre that used to be called progressive jazz. Bogatko's witty, fast-moving skatches, a pure delight in themselves, had a very special charm in Saturday's performance by Tafelmusik, the group for which the work was written.

One would think that Tafelmusik has no business playing jazz; it is a pristinely Baroque ensemble of flute (Lauren Weiss), oboe (Pamela Epple), cello (Christine Gummere) and harpsichord (Linda Kobler). But these four young women, in solos and various ensemble blends, demonstrated that you don't need saxes or drums to produce recognizable and dazzling jazz.

In immediate impact, the skatches outshone the main attraction of the program: the world premiere of "Feast-Day" by the brilliant young American composer Peter Lieberson. Commissioned to celebrate the 80th birthday of Irving Jurow, a benefactor of harpsichord performances at the Library of Congress, "Feast-Day" is a bright, busily descriptive, highly energetic and enjoyable piece that portrays a day of celebration in what sounds like a ancient but highly civilized society. Parts of it might sound a bit like parts of "The Rite of Spring" if it were not composed for an essentially Baroque instrumentation.

Elliott Carter's Sonata for Flute, Oboe, Cello and Harpsichord concluded the program. Carter's music, which once seemed rather austere and forbidding to the average music lover, is becoming more lyric and dramatic as it comes into the hands of a new generation of performers who take its structures for granted. Tafelmusik made it sound almost like easy listening.