The only way to inject some originality into a review of Kenneth MacMillan's dramatic ballet "Isadora," which the Royal Ballet premiered at Covent Garden in April and which had its Kennedy Center unveiling at the Opera House last night, would be to find something good to say about it. All the bad stuff has already been dished out by critics here and abroad who have tried to outdo one another in vituperative bravura. Audience reaction, according to reports, has been mixed -- they love it in Toronto, one hears -- and last night's crowd seemed moderately enthusiastic.

Alas, the price is too high -- it would take Voltaire's Dr. Pangloss to find something to praise in this exorbitantly hollow, tedious and misconceived extravaganza. The sad fact is that "Isadora" qualifies as an excruciating failure.

The most deplorable part of it is the way it demeans and abuses its intended heroine, Isadora Duncan, whose life story the ballet purports to tell. Worse still, MacMillan and his collaboratros end up trivializing Duncan's entire artistic contribution. It's impossible to believe this is what MacMillan had in mind to accomplish; his stated aims and his own dossier as a choreographer say otherwise. Nevertheless, that's the effect if you go by what you see on stage -- Isadora was a superficial, self-inflating poseur, who danced silly little plastiques to sugary salon music and slept around a lot.

Much of MacMillan's unassailable craftsmanship is still in evidence in large ways and small, but even in this respect he's fallen down in "Isadora." Despite the grand scale of the production, the flamboyand sex and other sensationalistic gambits, the ballet can't even sustain interest. Duncan is reduced to such a caricature there's nothing to be interested in , unless you go haywire over bedroom gymnastics on the dance stage. Most of the big dance numbers are instances of the pas de fornication , not so much dances as copulatory impressionism, stylized, tobe sure, but leaving, as they say, little to the imagination.

There's certain vestigial fascination in the dramaturgical structure and technique. MacMillan has consciously abandoned the conventional, neo-Petipa modes of his earlier dramatic ballets (of which his "Romeo and Juliet" is the best known) in favor of a deliberately "cinematic" approach, somewhat along the lines of Valery Panov's "The Idiot." The scenarist for "Isadora," Gillian Freeman, is also a screenwriter, and the ballet proceeds in fluid "takes" that fade out or disolve into one another.

The most conspicuous gimmick is the splitting of the role of Isadora into an acting and a dancing half, with actress Mary Miller doing the spoken part, and Merle Park the dancing. Though the illusion of a single character is fairly well maintained, the dialogue -- fabricated by Miller from Duncan's memoirs and other sources -- is one of the chief culprits in depriving us of any sense of reality in the character of Isadora. It's one thing to read Duncan's heavily artificed prose on a printed page, and another to hear it spoken -- mostly in the manner of a club luncheon orator -- in the midst of a ballet.

The music is another downer. Richard Rodney Bennett's original score, eclectic in style as it traverses contexts ranging from Isadora's recitals to Riviera soirees, is so plastic and banal in its effects it's no wonder MacMillan -- ordinarily very sensitive to musical impetus -- couldn't do much with it.

As for the dancing, there's scarcely enough to shake a stick at. The plot does follow Duncan's biography, at least in outline, but the long paragraphs of the choreography are taken up almost exclusively with her amours, and each one in turn is serviced by another erotic charade. The only other subject matter dealt with at length is the death of Isadora's children, but this is treated only in an ineffectual grief solo for Park, as far as dance is concerned.

The cast copes so well with the cartoon machinations of the ballet you can almost imagine they're enjoying it. But the only one who comes close to suggesting a flesh-and-blood personage is ever-reliable Derek Rencher in the relatively pallid role, as it is drawn here, of Paris Singer, Duncan's millionaire lover and benefactor. Oh yes, not to forget -- Barry Kay's elaborate, ingenious settings and costumes do their work admirably, setting period, atmosphere and emotional tonality. Maybe the ballet can be converted into a gallery exhibit -- it you took away the dancing, the music and the script, it might not be so terrible. "Isadora" will be performed tonight and tomorrow nights.