Celebration was the theme last night at Wolf Trap's gala concert marking the park's 15th anniversary and Catherine Shouse's upcoming 90th birthday. In a way, no program could have been more fitting for this popular performing arts center than the enduring, familiar tunes of Henry Mancini.

Liza Minnelli capped the evening with a glitzy nightclub act.

The program opened with one of the most festive groups in town, the Marine Band and Color Guard. After introductory remarks by assorted dignitaries, a taped Beverly Sills hosted a short film chronicling the career of Wolf Trap's founder.

Mancini strode onto the stage to the riveting strains of "Peter Gunn." The versatile composer, arranger and performer led suave medleys of some of his best-known works, and "The Pink Panther" and "Baby Elephant Walk" and the theme from "Charade" sounded as fresh as when they were introduced. The performance highlighted Mancini's originality and creativity in a time when works all seem to sound alike.

Minnelli and her band created a bold contrast to the easygoing Mancini. Her slick mixture of jazzed-up ballads, classic show tunes and current pop songs made for an awkward musical blend. But her energy and upbeat stage presence were unmistakable. Too bad that the artistic elements of her routine weren't more evenly balanced.