Even in these incestuous days, with plays - such as "A Chorus Line" - about plays, songs about songs and films about films, the idea in "Platinum," the new musical at the Kennedy Center's Opera House, is a terrible one. "Hey," says an aging rock star to the singers and technical people who work in a recording studio, "what would it be like to do an album about all of us?"

By the time he says this, we know what it would be like, because what he has recorded is the two hours of shop talk we have just been hearing. And as risky as it is to predict the record business, it seems safe to say that this album is not going to be a hit, not even if they put the male star's nude scene on the jacket and entitle it "Record Verite."

This is not to say that there are not some interesting things about "Platinum," which is about a '40s movie star trying to learn the '70s style to make a comeback.Alexis Smith gives an icily attractive performance as the actress whose only alternative to cultural retraining is to play "Mame" and "Dolly" on the road for the rest of her life. Lisa Mordente is funny as a diminutive rock star, sending off sparks and feathers from her outrageous costumes at the same time. Richard Cox has one charming song, about being part of a rock group that was able to afford buying a "movie-star mansion."

But the show isn't about anything; it's simply a jumble of popular-culture elements.

The tyranny of fashion in popular entertainment might have been served. Or the romance between an aging movie star and a rock star - who at 30 is also aging for his line of work - as part of the romance each feels for the other generation's style.

But no one has bothered to work any of this out. To begin with, the movie star comes in very expensive clothes, including sables, indicating that she does not have to work the run for the money. Does she then do it for love of the stage? She says not. Is the aura of money a sham? There is nothing to indicate this. Then why does she need to keep herself in any kind of show business?

The romance triangle between her and the male and female rock stars does not seem to affect any of them emotionally. At the slightest inconvenience, each of the three is cheerfully prepared to make other arrangements.

So we are left with no idea but the obvious one that audience tastes change over the generations, and the only way to survive that is to have the luck, as this star does, to hit a period of nostalgia for one's heyday.

The mix of media - there are closed-circuit television sets all over the stage set of a record studio - and of styles suggests a synthetic attempt to please all audiences. There are oldie songs, rock and a little folk-type. Looked at another way, there's something to offend everyone's tastes.