US STOCKS SNAPSHOT-Futures extend losses into Wall St open

NEW YORK Aug 10 (Reuters) - U.S. stock index futures extended losses on Wednesday after a sharp snap-back rally in the last session as investors' well-worn fears about the economy and high levels of public debt looked set to generate more volatile trading.

S&P 500 futures SPc1 lost 18.6 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures DJc1 fell 171 points, and Nasdaq 100 futures NDc1 dropped 38.25 points. (Reporting by Edward Krudy; editing by Jeffrey Benkoe)