ByJohn S. McClenahen The economic bulls have to be disappointed. The Conference Board's Index of Leading Indicators showed no change between January and February and stands at 112.4 (1996=100). However, the leading index is up 2.4% from its value six months ago and 3.1% from its value a year ago, stresses the New York-based business research group. Meanwhile, all four economic elements, including industrial production, that constitute the Conference Board's Index of Coincident Indicators increased in February. If modest gains in the coincident indicators continue, speculate the Conference Board's economists, the trend line will likely show that the low point of the most recent U.S. recession came in November of last year. The National Bureau of Economic Research, the official arbiter of U.S. recessions, figures the recession began seven months earlier, in March 2001.