Pegasus, as flutist Katherine Hay and pianist Frances Thompson McKay are collectively known, revives the art of improvisation in classical music. Tomorrow, as part of the first concert of the Contemporary Music Forum's season, Pegasus will present "Caravan," a piece that depends heavily on the participation of the audience, is minimally conducted by Hay and McKay and runs, maybe, for 10 or 15 minutes. There are no guarantees.

McKay and Hay describe their piece as the spontaneous translation of a visual image -- a caravan -- into sound: "It is very free and loosely structured." With eyes shut and minds open, the audience imagines itself standing "in the middle of a desert, watching a caravan coming towards them, arriving and going by"; they may also picture themselves participating in and traveling with the caravan. And what does a caravan sound like? Swooshing wind sounds, humming, and the cacophony of instruments that the Pegasus duo hands out (such as marimbas, ocarinas and bells) are strong musical possibilities. However it sounds, "Caravan" will be taped and, during intermission, audience members will have an opportunity to listen to their once-only interpretation.

"The sky is the limit as far as what you can do with improvisation," says Hay. "But there is a reward," adds McKay. "People come up with things that you've never thought of before."

Pegasus' "Caravan" will be created (or re-created) tomorrow evening in the Frances and Armand Hammer Auditorium of the Corcoran Gallery.