Think of all the talent it takes to write even a bad opera, someone once said. Well, a lot of talent has gone into "Timbuktu!," the black version of "Kismet" which opens Saturday at the Kennedy Center's Opera House.

There are beautiful and fascinating ingredients in it: a bird ballet, the swirl of costume and color, Eartha Kitt. But as of preview time, these did not compensate sufficiently for its tremendous problems.

Two of the problems are relatively easy to fix. Cut down from three hours to two and a half, it still needs at least half an hour more to be taken out. And the sound system is offensive. Operating at full blast, it turns strong notes into screeches, and gives one the impression that the singers on stage cannot be producing all that noise.

More difficult to correct will be the tone of the show. "Kismet" was a solid musical a generation ago, and I see nothing wrong with transferring the locale in order to present it with a black cast. Timbuktu of the 14th century has all the attributes of exotica of the Arabian Nights, and a black version makes as good sense as a white. But not if the actors behave like hip young people of today who can't figure out how they got caught in this silly tale.

It is a silly tale, of course, but standing back from it in amazement at its silliness doesn't help. Even the thigh-flashing royal guards, some of whom must be seven feet tall, seem to shrink as they relax their posture after dancing to become your street-philosophical modern cop-on-the-beat.

Eartha Kitt has made the only success in this respect. It does not hurt that she has the world's most exciting voice, which puts wit and worldliness into the most banal lines. The best moment of the show is when she makes a rather elaborate entrance and then announces merely, "I'm here."

But what she has done is to take the character we know from her songs, the woman who can make sophisticated boredom sound like a wonderfully sensuous new sin, and made a creditable place for her in legendland.

Melba Moore has done the opposite. It is admittedly a chore to be cast as an urchin with whom a powerful ruler falls instantly in love, but Moore's contempt for the fairytale aspect of her role keeps showing. She's fine as a juvenile delinquent, but Cinderellas must display some natural nobility under their rages, and she does not. One feels here that the royal bridegroom would be well advised to spend some time after the wedding banquet counting the spoons.

When you add up the assets and liabilities, "Timbuktu!," as of preview time anyway, is not a success. But it is not the kind of failure that makes you feel gypped; rather, the kind that makes you hope it will be saved.