One of the problems facing contemporary audiences who try to imagine what Isadora Duncan could have been like is that Isadora the Legend has swallowed Isadora the dancer. Add to this the fact that Duncan's dances were neither filmed nor notated, and probably the only way we can experience her is through a peotic evocation, such as Colette Yglesias presented Saturday afternoon as part of the National Portrait Gallery's "Portraits in Motion" series.

Yglesias doesn't have the larger-than-life presence that was reputedly Duncan's; she would undoubtedly be unconvincing dancing to Wagner on a large stage. But in the intimate atmosphere of the Gallery's Great Hall her interpretations of three Chopin piano pieces captured the sincerity, womanliness and chasteness that is a large part of what we associate with Duncan.

Both Yglesias' "Mazurka" and "Nocturne" are gentle pieces that show Duncan's worship of nature, the dancer skipping, running, perhaps in wind and rain -- a Greek nymph playing in an idyllic setting. In "Prelude" Yglesias is sweetly heroic as she performs with the unabashed sentimentality that was Duncan's style expressing emotion with note-for-note literalism.

Yglesias was accompanied on the piano by Pierre Fournier, who was attired in white tie and tails -- a nice touch. The short speech she made before her performance was unnecessary.Her dances speak for themselves and her view of Duncan as solely responsible for all reforms in the 20th-century dance is naive. The excellent program notes by Gretchen Schneider, rich in historical and esthetic detail, would have been sufficient.