Economists predict a stronger stock market, improved consumer confidence and fewer jobless claims will help lift a September index of leading economic indicators. The New York-based Conference Board's monthly forecast of future economic activity -- due out Thursday at 10 a.m. EDT -- is expected to show the index gained 0.4 percent last month, according to the consensus estimate of Wall Street economists surveyed by Thomson Financial/IFR. However, economists' latest estimates ranged from a decrease of 0.3 percent to a gain of 0.6 percent. The index is designed to forecast economic activity over the next three to six months and includes 10 economic components. It decreased 0.6 percent in August largely due to lower consumer expectations, higher unemployment insurance claims, declining housing permits and weaker stock prices and interest rate spread, five of the 10 components. The index stood at 137.8 in August. In 1996, it was 100. Although the index has fluctuated in the last few months -- a 0.7 percent increase in July, a 0.1 percent fall in June and 0.2 percent gain in May -- the cumulative change over the past six months has been a 0.5 percent rise. The Conference Board said last month that economic growth will likely continue in the near term, but at a slower pace. The index's other components include vendor performance, inflation-adjusted money supply, average weekly manufacturing hours worked, manufacturers' new orders for consumer goods, and manufacturers' new orders for capital goods.