Standard & Poor’s Ratings Services on Friday affirmed its AA+ long-term credit rating on the U.S., still a notch below the coveted AAA rating, while maintaining a long-term negative outlook.

The ratings service said its sovereign credit ratings on the U.S. “primarily reflect our view of the strengths of the U.S. economy and monetary system, as well as the U.S. dollar’s status as the world’s key reserve currency.”

However, S&P said U.S. political and fiscal sovereign credit risks could lead it to lower that rating by 2014.

In a statement released after the close of U.S. stock markets, S&P said, “We see the U.S. economy as highly diversified and market-oriented, with an adaptable and resilient economic structure, all of which contribute to strong credit quality.”

In addition, S&P said it believes the Federal Reserve “has an excellent ability and willingness to support sustainable economic growth.”

Meanwhile, S&P said its current rating for U.S. credit also take into account the high level of U.S. debt and S&P’s long-held view that U.S. fiscal leaders have been ineffective in dealing with those debt problems.

The statement cited several examples in recent years in which Congress and the Obama Administration tried to reach agreement on fiscal reform but were unable to because of dueling ideologies.

“We view U.S. governmental institutions (including the Administration and Congress) and policymaking as generally strong, although the ability to implement reforms has weakened in recent years because of a sometimes slow and complex decision-making process, particularly with regard to broad fiscal policy direction,” the statement reads.

Moreover, the negative outlook reflects the fact that the U.S. economy has shown increased signs of weakness recently, according to the statement.

Last summer S&P rocked financial markets by lowering the U.S. credit rating below AAA, an unprecedented move designed to send a warning shot to U.S. fiscal policy makers to get their act together.

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