Stock index futures fell on Wednesday as a drop in commodity prices looked set to weigh on shares of natural resource companies and investors digested the impact of an overnight sell-off in Chinese stocks.

The selling added to the cautious tone generated by concerns that banks may begin to restrict lending in China to take some of the froth off the market.

Concerns about China also weighed on global commodity prices, with U.S. front-month crude falling 2.4 percent or $1.59 to $65.65 a barrel. The Select Sector SPDR Energy exchange-traded fund declined 1 percent.

To the extent that we're up 40 percent from the March lows it only makes sense to have some sort of pause and reflect on what valuations look like, said Arthur Hogan, market analyst at Jefferies & Co in Boston. Part of the story in commodities' success has been the China demand story.

S&P 500 futures shed 5.70 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 dipped 40 points, and Nasdaq 100 futures were off 7 points.

Key economic reports due on Wednesday include data on June durable goods at 8:30 a.m. EST (1230 GMT), and the Federal Reserve's Beige Book at 2 p.m. (1800 GMT) -- which is the central bank's snapshot of regional economic conditions.

Yahoo Inc shares fell 3 percent to $16.70 in premarket trade after the Internet media company reached an online search and advertising partnership with software giant Microsoft .

S&P 500 stock index futures had dropped more than 1 percent earlier, driven lower by a 5 percent slide in Chinese shares <.SSEC> -- their biggest daily decline in eight months -- on worries that authorities might take measures to cool the 80-percent gain in Shanghai shares this year.

In Tuesday's trading, the Dow and the S&P 500 fell slightly, recovering from earlier declines as investors shrugged off weak consumer confidence data and focused on positive earnings reports. But a rise biotechnology shares helped the Nasdaq to post a gain.

(Reporting by Ellis Mnyandu; Editing by Padraic Cassidy)