Its only speculative how much impact it had, but an unusual joint statement by two traditional antagonists -- the U.S. Chamber of Commerce and the AFL-CIO -- may have helped influence Tuesdays decision by the Federal Reserve to lower short-term interest rates by a quarter percentage point. Chamber President and CEO Thomas J. Donohue and AFL-CIO President John J. Sweeney issued a joint appeal for lower rates on Monday, declaring that an economic slowdown rather than inflation is the pre-eminent danger confronting the American economy. The statement represents growing cooperation between the two Washington, D.C.-based-organizations. At Donohues invitation, Sweeney spoke to the Chambers board of directors on Nov. 11. In return, Donohue will speak at the AFL-CIOs annual meeting in Florida early next year. Sweeney told the Chamber board that the two groups could do some terrific things together in such issues as workforce-development, health care, education, and retirement security. Yet, he told the Chamber leaders, there isnt much chance of getting together when you want to deny our unions the very right to exist and deny workers and their families a decent share of the wealth they produce.