This is from Lyle McDonalds site:
UNDER DIETING CONDITIONS CONT...Training - As noted above, at least some volume of heavy training should be done while dieting to maintain current strength and muscle mass levels. However, research clearly shows that the volume and frequency of training can be cut back rather significantly.Reductions in both of up to 2/3rds (so total sets and/or days of training can be reduced) are fine but ONLY if the intensity (weight on the bar) is maintained. So an athlete who was doing 6 sets of 3 in the back squat could conceivably cut back to 2 sets of 3 as long as he keeps the weight on the bar the same. If the intensity is cut back, strength and muscle mass will suffer.