If all children's opera could be as good as Wolf Trap's "Hansel and Gretel," the audiences would more than triple. In the last presentation of its free Saturday Operas in the Park, the members of the opera training program brought Humperdinck's Wagneria fairy tale to life, delighting a very demanding audience of budding opera fans.

The setting was perfect on Saturday morning. On a stage literally hidden in the woods, the action was surrounded by tall trees and summer breezes. Robert Alper's patchwork quilt designs blended to perfection with all the greenery. With Adelaide Bishop's frantic and tight direction, there were some delightful surprises. The woods sounds really came from the woods, with an appreciative hush falling at appropriately spooky moments.

Sandra Ruggles was a wonderful Gretel, cute without being cutesy, and musically one could not ask for more from this small but warm and intelligently produced voice. Marnie Clark was a hooty Sandman, and Beverly Hoch, soaring in from the woods, was among the best in a long tradition of high coloratura fairies. Christine Shadeberg, a very evil witch, captured her audience's good favors by throwing candy at them in the curtain calls. The little angels with golden wings who danced over the sleeping children received admiring applause. The small ensemble conducted by Hal France at times actually suggested the huge Humperdinck orchestration. And size was only compromise. In every othere way, this was a "Hansel and Gretel" to please opera experts of any age. As the 10-year next to me said, "It's better than just the story, 'cause the musci's so pretty." Amen.