Sitting through the new "Isadora" at the Kennedy Center a second time proved to be almost as absorbing an experience as the premiere Tuesday. Other multi-act story ballets of post-World War II vintage often tempt this member of the audience to fidget or doze, but then "Isadora" isn't really a ballet at heart but a play, a monodrama, illustrated with movement and dance.

The creation of this piece for Britain's Royal Ballet must have resembled the making of an old movie biography. Data was amassed on Isadora Duncan, "the first modern woman and first modern dancer." A story was built on accurate details that add up to a nearly fictional plot. Yet, a powerful image was created through imaginative sterotyping. In this instance, it is the image of the American woman as someone who flowers freely and decays grossly.

The portrait is not one Americans like, but it strikes home and comes to life in a stunning performance by Mary Miller. Her Girl of the Golden West accent, projected with skilled English elocution, was winning. In the midst of burlesque and grande guignol, Isadora spoke with her soul. It is to choreographer Kenneth MacMillan's credit that he saw how Miller was growing in the role and gave her the right of way. The dancing Isadora is definitely a supporting role.

Fiona Chadwick, who was new in the dancing part last night, doesn't have the ability to rivet the beholder immediately that Merle Park showed at the opening. But when Chadwick moved there in moments of dynamic spaciousness, supple strength and gravity that may not really be Duncanesque but have a freedom that is the result of will, not accident.

Wayne Eagling, new as Isadora's great love, Gordon Craig, gave the character a richly sullen air. Antony Dowson, new as the son-lover, Esenin, had the boyishness but not the anger and abandon of Stephen Jefferies' opening night portrayal.

Tonight is Miller's last Isadora, with Merle Park as her dancing ego.