By John S. McClenahen Many manufacturing executives and workers would like to believe that layoffs and other cost-cutting measures are pretty much behind them. They may not be. Companies probably won't be able to sustain price increases that would significantly improve their earnings. Productivity increases will likely help. "Productivity . . . should improve further during the first year or two of a recovery, another plus for margins," believes Bruce Steinberg, chief economist at Merrill Lynch & Co., New York. "Nevertheless," cautions Steinberg, "with little pricing power, the need to restructure and cut costs will likely persist well into the expansion."