Stocks headed for a lower open on Friday as a pullback in commodity prices weighed on natural resource shares after the U.S. dollar rebounded.

The dollar rose broadly after Federal Reserve Chairman Ben Bernanke said that monetary policy might have to be tightened as a recovery takes hold.

The dollar's decline, which culminated in a 14-month trough against a basket of currencies on Thursday, has been one the major underpinnings of the stock market's run-up as the appetite for riskier assets grew.

Mining shares fell before the bell, with Freeport-McMoran Copper & Gold Inc off 0.8 percent to $74.37, and Newmont Mining Corp down 1.3 percent to $46.40.

In the energy sector, shares of ConocoPhillips fell 0.8 percent to $51 before the bell. U.S. front-month crude declined nearly 1 percent, while gold eased after hitting records for three straight sessions.

There's focus on the dollar following Bernanke comments overnight, said Peter Boockvar, equity strategist at Miller Tabak & Co. The weaker dollar has been good for asset classes, and at some point that will break.

S&P 500 futures dipped 2 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 shed 13 points, and Nasdaq 100 futures fell 8.50 points.

U.S. stocks rose for a fourth straight session Thursday as a surprising quarterly profit from aluminum company Alcoa Inc got third-quarter earnings off to a strong start. The benchmark S&P 500 <.SPX> has rallied nearly 60 percent from a 12-year low of early March.

(Reporting by Ellis Mnyandu; editing by Jeffrey Benkoe)

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