In a program that included many classics of popular song and other works that sound like potential classics, Elly Stone selected her material with exquisite taste and a fine series of balance last night at Wolf Trap. After a few problems in the opening numbers, she performed beautifully such items as Jacques Brel's "Carousels," "No Bed of Roses" from "Mahagonny" and a well-chosen medley from "Threepenny Opera." This medley climaxed with "Mack the Knife" sung in very good German, but its finest interpretive moments came in the difficult, powerful "Pirate Jennie."

The second half ranged back and forth between songs of rather mild social protest and very intense comedy. It was highlighted by a performance of John Cage's "Four Minutes and Thirty Three Seconds." Since this was a performance for an audience not usually familiar with Cage, two words, "Of Silence," were added to Cage's title, making clear what was supposed to be happening but somewhat reducing the element of surprise.

A dominant personality of the evening was Eric Blau, whose works Stone made sound almost equal to the giants of the program -- no small accomplishment.

The only serious problem of the evening was the sound mixing, done by Stone's own technicians. I sampled it from various parts of Wolf Trap and found it completely satisfactory only on the lawn, where it sounded like a good high-fidelity system. Elsewhere, it sounded like a bad high-fidelity system. Despite any sonics obstacles, Elly Stone's polished and persuasive art managed to come across.