U.S. stocks were little changed on Monday as concerns over European debt offset gains in natural resource shares, lifted by a bounce-back in commodities.

Standard & Poor's once more downgraded Greece's debt rating, saying there is increased risk Athens will restructure its private debt.

The rating cut weakened the euro against the U.S. dollar, shaving gains off commodities and reducing some risk appetite that earlier had lifted futures.

Europe's problems have gotten worse, said Shawn Hackett, president at Hackett Advisors in Boynton Beach, Florida.

Demand in commodities was already being destroyed by the high prices, and the dollar is making commods now more expensive.

The energy and materials sectors were the best performers on the S&P 500 as the Reuters/Jefferies commodities index <.CRB> jumped more than 1 percent.

The iShares Silver Trust exchange-traded fund rose 4.1 percent to $35.90.

But Hackett, who specializes in commodities, said if the large declines last week were perceived as exaggerated, Monday's bounce-back would have had to be stronger.

We're in a bear market in commodities, Hackett said. The stock market is really in trouble.

Commodities, stocks and the euro have traded in a similar pattern in recent months as low interest rates in the United States boosted risk appetite.

The Dow Jones industrial average <.DJI> gained 24.10 points, or 0.19 percent, to 12,662.84. The Standard & Poor's 500 Index <.SPX> rose 2.63 points, or 0.20 percent, to 1,342.83. The Nasdaq Composite Index <.IXIC> added 5.48 points, or 0.19 percent, to 2,833.04.

On the S&P 500, 1,340 and 1,333 are key levels that should provide strong support and entice buyers according to Ryan Detrick, senior technical strategist at Schaeffer's Investment Research.

Despite last week's losses, the S&P 500 held above important technical levels, with the week's low just below 1,330 and Friday's close above 1,340.

Among companies reporting earnings Monday, SYSCO Corp gained 10.2 percent to $31.41. About 70 percent of S&P 500 companies that have reported results have beaten expectations.

Relatively low volume so far this year could see a further decline as Citigroup Inc's 1-for-10 reverse stock split comes into effect Monday. Citi shares have recently accounted for about 6 percent of composite volume.

Citi shares traded at $44.93 after closing at $4.52 on Friday.

(Reporting by Rodrigo Campos; Editing by Kenneth Barry)