Stocks were little changed in choppy trading on Tuesday, with cautious investors hoping S&P's downgrade warning for the euro zone would help force budget changes at a European Union summit this week.

Bank stocks, recent outperformers in the U.S. market, kept a lid on gains, with the S&P financial sector down 0.5 percent.

Rating agency Standard & Poor's said Monday it may cut the sovereign credit rating of 15 euro zone countries. The warning was leaked during market hours, and U.S. stocks halved their session's gains.

Futures traded mostly higher heading before the open, but indexes hovered around break-even in early trading. Peter Jankovskis, co-chief investment officer at OakBrook Investments in Lisle, Illinois, said the initial resilience was surprising.

We've seen a pattern where there has been talk of an agreement, and when it comes down to the details there's nothing substantial at all, Jankovskis said.

Still, he said S&P's warning is viewed as something that could hold (euro zone) leaders' feet to the fire and force them to go through with a comprehensive solution.

The Dow Jones industrial average rose 33.45 points, or 0.28 percent, at 12,131.28. The Standard & Poor's 500 Index was down 0.16 points, or 0.01 percent, at 1,256.92. The Nasdaq Composite Index dipped 4.31 points, or 0.17 percent, at 2,651.45.

France and Germany were planning to force changes to EU rules in hopes of restoring market confidence and preventing the two-year-old sovereign debt crisis from widening.

Dow component 3M Corp rose 1.8 percent to $82.35 after the diversified manufacturer forecast 2012 earnings and revenue largely in line with expectations as well as modest margin improvement.

Darden Restaurants Inc fell 10 percent to $43 after it cut its fiscal 2012 earnings and sales forecast.

(Reporting by Rodrigo Campos; editing by Jeffrey Benkoe)