There were times Saturday night at Constitution Hall when the Temptations' reunion concert (the first of three performances) seemed as much a bring-down as a comeback, thanks to a sound system that consistently strove for new highs in low fidelity.

But to dwell on the unnecessarily loud volume, low-end distortion and intermittent feedback that made savoring the Temptations' wonderful vocal blend next to impossible would be unfair. For in spite of it all, the seven Temps, resplendent in white tie and tails and backed by a 16-piece orchestra, put on a thoroughly enjoyable, if hardly inspired, 90-minute show.

Ninety minutes, of course, hardly seems enough for a group that has 20 years of memories to share. As always in shows of this kind, many of the hits were reduced to medley form, but some of the best songs--"My Girl," "Ain't Too Proud to Beg," "I Wish It Would Rain"--survived more or less intact and still managed to send tingles up and down the spine.

It was Dennis Edwards, instead of recent returnees David Ruffin or Eddie Kendricks, who stirred the crowd most often. Ruffin was in good, raspy voice but occasionally seemed to be going through the motions; Kendricks, sporting a perpetual grin, seemed unsure of his falsetto and used it cautiously. Edwards' voice, on the other hand, was emotion laid bare.