Stock index futures rose on Tuesday as investors hoped S&P's downgrade warning on the euro zone's credit ratings will help force through budget changes at a European Union summit this week.

The euro and most European stock markets edged lower after rating agency Standard & Poor's warned 15 countries it may cut their sovereign credit ratings.

The S&P warning may help France and Germany change European rules, restore market confidence and prevent a sovereign debt crisis from spiraling out of control.

There's an idea the S&P warning is likely to push the EU to work harder at solving its debt crisis, said Rick Meckler, president of investment firm LibertyView Capital Management in New York.

The warning may have the impact of pushing forward the solution without having to be an actual problem to the market.

S&P 500 futures rose 3.3 points and were above 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 gained 52 points, and Nasdaq 100 futures added 12 points.

The S&P threat could help French President Nicolas Sarkozy and German Chancellor Angela Merkel force through a change to the EU treaty at a summit December 9. They are determined to impose penalties on countries that exceed deficit targets.

Traders were also encouraged by a dip in Italian benchmark bond yields, which had soared close to 8 percent, threatening government financing and bringing it closer to a sovereign default.

Every time yields come down, it gives (Italy) a little more room to survive until reforms are put in place, Meckler said.

The yield on Italian 10-year notes was at 5.886 percent, the lowest since late October.

The S&P warning was leaked during market hours in the United States on Monday, deeply cutting into stock gains.

(Reporting by Rodrigo Campos; editing by Jeffrey Benkoe)

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