Wall Street was set to open lower on Wednesday on worries over Greece's ongoing financing woes and ahead of an auction of 10-year Treasury notes coming amid concerns about rising yields.

The Treasury will sell 10-year notes as the prospect of a stronger economy has pushed the yield on the note -- a benchmark for mortgage rates -- up toward 4 percent. Investors worry if rates go too high, it may damage a housing market that is struggling to recover.

European stocks <.FTEU3> fell 0.4 percent on renewed concerns about the credibility of Greece's aid package as a top Greek official said local banks, hit by a series of credit rating downgrades, asked for more financial support.

That (Greece) seems to be the one issue that cannot be dealt with in short order, said Peter Kenny, managing director at Knight Equity Markets in Jersey City, New Jersey. It's part of the euro zone and the implications are enormous, it's the elephant in the room.

Federal Reserve Chairman Ben Bernanke is due to speak on Economic Challenges: Past, Present and Future at a Dallas luncheon. Investors will scour his testimony for clues about the Fed's thinking on interest rates and the economy, given recent better-than-expected economic data.

S&P 500 futures fell 4.6 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 dropped 31 points, and Nasdaq 100 futures lost 5.75 points.

U.S. equities have had five weeks of gains, pushing major indexes to highs not seen in a year and a half. The Dow could pierce the psychologically important 11,000 level.

The market has had a nice run here, said Cardillo. It's only natural to have some profit taking without any real catalyst to move the market higher.

Shares in Family Dollar Stores Inc rose 4.6 percent to $39.52 in premarket trading after the discount retailer reported higher-than-expected quarterly profit on a boost from longer store hours and sales of private label items, and forecast earnings that should top estimates.

Monsanto Co fell 1.4 percent to $68.83 premarket after the agricultural seed company said profit fell below expectations and warned that intensified competition will make it difficult to meet its targets.

(Reporting by Edward Krudy; editing by Jeffrey Benkoe)

Ben Bernanke