Listening to on aging diva perform has its hazards and its rewards. When Maria Callas gave her farewell concerts, for example, audiences were treated to the spectacle of a voice post its prime trying to recapture former glories. There was pathos in the legendary soprano's seeming acknowledgment of her decline, yet there was also poignance in her attempt to assert her superb artistry. The Spanish soprano Victoria de los Angeles, by most accounts, still has her remarkable voice at age 70. It's said to be smaller in range and strength, but not lacking in luster or vibrancy. De los Angeles made her debut a half century ago in her native Barcelona. In the 50s she was the toast of the world's opera stages, from La Scala to the Met, specializing in dramatic roles well-suited to her peculiarly luminous soprano. Her Mimi, Marion, and Cio-Cio San were memorable, and the Thomas Beecham recording of her world-weary Carmen is justly celebrated. During her stay at Ravinia this week, de los Angeles will import her wisdom to a new generation of singers in master classes at the Steans Institute for Young Artists. For those who turn up at the recital, she's compiled a thick anthology of old standbys. The songs of Caccini, Faure, Garcia Lorca, and Granados are charmingly atmospheric and not overly taxing. The lieder of Brahms may be a bit out of her range now, but one can count on the veteran in her to bring forth their poetic ardor. Accompanying de los Angeles on the piano is David Owen Norris, an estimable musician who's in charge of the vocal program at the Steans Institute this summer. Monday, 8 PM, Murray Theatre, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642.