Today's task: Think of a simile to describe the casting of Roberta Peters in "The Sound of Music." Examples: It's like driving a Porsche at 20 mph. It's like using a yacht to cross the Potomac. It's like asking Michelangelo to design a logo. It's like . . . Never mind. You get the idea.

Another question, and one that is not a game, is why a woman with a voice like hers is wasting her time in a tedious piece of corn like the one that opened at Wolf Trap last night. There is such a thing as good corn, and Rodgers and Hammerstein in their prime produced plenty of it, including that which was as high as an elephant's eye. But "The Sound of Music" was their last collaboration before lyricist Hammerstein's death, and by that time the formulas worked only when interpreted by the most skilled managers.

Peters is too old for the part of the innocent young novitiate-turned-governess (she has the courage to say in the program that she made her debut "some 30 years ago" at the age of 19), but that is the least of this production's problems. Indeed, she manages to be quite convincing as the youthful Maria, especially if your seat is in the second half of the auditorium. The other problems are beyond her efforts to conquer: a script that is a virtual festival of cliche's, songs that would give Shirley Temple cavities, and performers who, with few exceptions, plod through these handicaps without surmounting them.

Is it that we live in a different era than we did 23 years ago when this show opened? Perhaps. But the story is basically a good fairy tale, with the added cache of being based on a true story, and good fairy tales generally last. A naive girl, pure of heart but too independent to give her life to God, is sent to be governess to a brood of rich, motherless children. She teaches them to sing, makes them happy and marries their father, just as the shadows of Hitler's Third Reich are falling on Austria, precipitating a moral crisis for the children's father, Captain Von Trapp (Theodore Bikel). He, naturally, elects the more difficult but morally correct course and flees with his family, leaving his homeland and wealth for an uncertain future. Fairy tales can make wonderful musicals, but this one is so laden with pompous sentimentality that the emotion is suffocated.

There are many moments of clumsy predictability that create a sense of self-conscious theatricality, and a quality of buttons being pushed artlessly. In one scene, for example, the children, frightened by a thunderstorm, tumble into Maria's attic room. "Maybe if we all sing loud enough we won't hear the thunder!" she says chirpily, taking position for the inevitable song to follow.

Of course, even the corniest exchange or song would be improved if the microphones didn't spit static every time a performer moved. One can forgive the painted backdrops that move with every breeze, even admire their quaintness, but it is hard to accept the presence of stage hands hustling out to change scenery before the curtain has closed.

And through it all is the lovely fluid voice of Roberta Peters, who sails through the simple and often beautiful music like a hot knife through butter. But it seems like a job for which she is clearly overqualified.

"THE SOUND OF MUSIC," produced by Lee Guber and Shelly Gross, music by Richard Rodgers, lyrics by Oscar Hammerstein II, book by Howard Lindsay and Russel Crouse, directed by Jay Harnick, choreography by Judith Haskell, musical direction by Milton Rosenstock. With Roberta Peters, Theodore Bikel, Woody Romaff, Marni Nixon, Anita Darian. At Wolf Trap through Sept. 5.