Stock index futures tumbled on Tuesday as the deal to rescue Greece and prevent a wider sovereign debt crisis faced a new hurdle and as Asian economic data reignited fears of a slowdown in global growth.

Greek Premier George Papandreou said he will put Greece's bailout deal through a referendum, throwing the long-awaited deal into disarray and sending European stocks down 3.5 percent. The region's bank shares fell 6 percent.

U.S. bank shares were expected to follow European lenders lower. The Financial Select Sector SPDR fell 2.3 percent in light premarket trading.

The market did not see this Greek referendum coming, which is potentially a killer and could knock the wheels off the bus of the whole (European rescue) plan, said Paul Mendelsohn, chief investment strategist at Windham Financial Services in Charlotte, Vermont.

Most Asian stock markets fell after data showed factory activity in the region's export powerhouses slowed to near three-year lows in October on lower European demand, reinforcing fears the euro zone's debt troubles were sapping global growth.

S&P 500 futures dropped 26.6 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures lost 157 points and Nasdaq 100 futures slid 41.75 points.

S&P 500 futures fell below their 14-day moving average for the first time since October 6 early Tuesday, pointing to a possible shift in short-term momentum. Stocks closed on Monday their best month in 20 years.

China's factory activity last month was its slowest since February 2009, the government said, an unexpected decline that reflected a drop in new export orders. The overall index dipped to 50.4 from September's 51.2, edging closer to the 50 line that separates growth from contraction.

In a move that could further weigh on commodity prices and risky assets, Japan vowed to step into foreign exchange markets again to curb excessive speculation. The government reportedly sold a record 7.7 trillion yen ($98.7 billion) Monday to curb the yen's strength, which is hurting its export-based economy.

The U.S. dollar index rose 1.5 percent. U.S. oil futures dropped 2.7 percent and copper prices fell 3.8 percent.

In the United States, the ISM Manufacturing Index is expected to edge up to 52.0 in October from 51.6, based on a Reuters poll. The data is due at 10 a.m. EDT (1400 GMT).

The Federal Open Market Committee kicks off its two-day policy-setting meeting later Tuesday. The FOMC is likely to take a break from policy changes after two consecutive easing actions.

Pfizer Inc, the world's biggest drugmaker, reported better-than-expected quarterly results early Tuesday, and its shares rose 1.3 percent to $19.50.

(Reporting by Rodrigo Campos; editing by Jeffrey Benkoe)

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