By John S. McClenahen Great gains in U.S. productivity are laying the groundwork for what's likely to be a strong expansion, claims Merrill Lynch & Co., New York. Purchasing and supply executives in the manufacturing sector of the U.S. economy are said to be the more optimistic about the U.S. economy than at any other time in the past year. But Don F. Carlson, president of AMT -- The Association for Manufacturing Technology, is worried. "I'm concerned that the over-valued [U.S.] dollar threatens all manufacturers' health and will put an end to this recovery before it truly gets underway." The recovery clearly hasn't gotten underway for the machine tool builders that his trade association represents. Although gross new orders for U.S. consumption were up 6% between February and March to $182.66 million, first-quarter 2002 orders were $513.62 million, 35.2% below the first-quarter 2001 figure of $792.32 million, report McLean, Va.-based AMT and the American Machine Tool Distributors' Association, Rockville, Md. Orders for metal-cutting machine tools were $476.74 million in the first of this year; orders for metal-forming tools were $36.88 million.