The most durable harmonica and guitar blues duo this side of Sonny Terry and Brownie McGhee performed at the Wax Museum last night under what they considered less than ideal conditions. Junior Wells and Buddy Guy, veteran bluesmen, who cut their teeth in Chicago clubs in the '50s and have been playing together on and off ever since, were clearly unhappy with the scheduling of their performances.

Both expressed dissatisfaction with the proposed brevity of their first set, which was about 45 minutes long, and Guy, in particular, seemed preoccupied with the matter. A spokesman for the Wax Museum could not be reached for comment.

A superb blues guitarist with biting tone and a strikingly plaintive voice, Guy only briefly managed to display his mastery of the idiom on "Dust My Broom" and "Five Long Years," and even then his playing was occasionally tentative. With an eye presumably on the clock, he then abruptly ended his part of the concert to introduce his partner.

Wells, though, insisted on extending the set. Augmented by a solid backbeat and Guy's acerbic punctuations, Wells turned in a series of soulfully expressive performances, commenting on the harmonica whenever words failed him. Particularly impressive was his tribute to his mentor, Sonny Boy Williamson, the centerpiece of which was a genuinely heartfelt version of Williamson's classic blues "Help Me."