By John S. McClenahen Despite the fact that U.S. consumers, whose outlays account for about two-thirds of U.S. GDP, keep spending at relatively high levels, they aren't all that happy about the near-term economic future. The consumer confidence index compiled by the Conference Board, a New York-based business research group, fell to 76.8 (1985 = 100) last month, nearly five points below August's 81.7. The percentage of respondents to the group's Consumer Confidence Survey anticipating the U.S. job market to improve in the next six months fell to 16.7% in September from 18% in August. Those expecting fewer jobs to become available increased to 21% from 18.6%. The survey is based on a representative sample of 5,000 U.S. households and is conducted for the Conference Board by NFO WorldGroup.