Perhaps for the first and last time, the words "power failure" and "Ben Vereen" were linked together at Wolf Trap on Saturday night. A partial power failure affecting the stage lights caused Vereen to begin his concert a few minutes late, but if the problem ever occurs again, technicians would do well to harness Vereen himself. His frictionless hips alone were enough to light up every smile in the place.

Vereen isn't one to go through the motions on stage; he is the motion. Like a prizefighter going the distance, he weighs a lot less leaving the main event than he did upon entering.

For Vereen, the distance is an often-exhausting 90 minutes. The first part of the show featured a number of ballads sung in a warm, if hardly distinctive, fashion. This was leisurely compared with what came later: sensuous, sometimes heated reminders of "Pippin" and "All That Jazz" floated on a cushion of glides, strides, swivels and strides a la Bob Fosse; and Fats Waller's "This Joint Is Jumpin' " demanded and received handstands, cartwheels and scissor splits. Other songs, including a galvanizing version of Stevie Wonder's "Master Blaster" were delivered face-to-face with Vereen sprinting from the stage to the lawn and back again, a throng of fans in hot pursuit.

Did someone mention power failure?