U.S. stocks extended losses on Monday, sending the S&P 500 index down 1 percent, after a weaker-than-expected reading in a forward-looking measure of the U.S. economy.

* The Conference Board's August index of leading indicators rose 0.6 percent, marking a fifth straight monthly increase, but was shy of the 0.7 percent forecast by economists.

* The Dow Jones industrial average <.DJI> was down 86.76 points, or 0.88 percent, at 9,733.44. The Standard & Poor's 500 Index <.SPX> fell 9.88 points, or 0.92 percent, at 1,058.42. The Nasdaq Composite Index <.IXIC> dropped 11.17 points, or 0.52 percent, at 2,121.69.

* The latest data provided selling impetus, but the market was already lower as a resurgent U.S. dollar took a toll on global commodity prices and investors paused to gauge if the outlook for corporate profits justified the market's recent run-up to 11-month highs.

(Reporting by Ellis Mnyandu; editing by Jeffrey Benkoe)