Two leading credit rating agencies on Thursday warned the U.S. on its credit rating, expressing concern over a deteriorating fiscal situation that needs correcting.

Moody’s Investors Service Inc. said in a report Thursday that the U.S. will need to reverse an upward trajectory in the debt ratios to support its Aaa rating.

“Further actions will be necessary to avoid an unfavorable debt trajectory, which would increase the probability of a change to a negative outlook on the Aaa rating,” Moody’s said in a report.

Standard & Poor’s Corp. on Thursday also didn’t rule out changing the outlook for its U.S. sovereign debt rating because of the recent deterioration of the country’s fiscal situation.

The U.S. currently has a triple A rating with a stable outlook at both agencies.

“The view of markets is that the U.S. will continue to benefit from the exorbitant privilege linked to the U.S. dollar” to fund its deficits, Carol Sirou, head of S&P France, said at a Paris conference Thursday.

“But that may change. We can’t rule out changing the outlook” on the U.S. sovereign debt rating in the future, she warned.

She added the jobless nature of the U.S. recovery was one of the biggest threats to the U.S. economy. “No triple-A rating is forever,” she said.

Moody’s said the U.S., Germany, France and the U.K. still have debt metrics, including debt affordability, compatible with their Aaa ratings at Moody’s.

But all four countries must bring the future costs arising from pension and healthcare subsidies under control if they “are to maintain long-term stability in their debt burden credit metrics,” Moody’s said in its regular Aaa Sovereign Monitor report.

Moody’s referred to the U.S. National Commission on Fiscal Responsibility and Reform, appointed by President Obama, and its package of measures to achieve a balanced primary budget by 2015, which failed to get sufficient support to trigger consideration by the full Congress.

The recommendations included a wide variety of measures, including Social Security reform, cutbacks in the growth of Medicare outlays, elimination or modification of the mortgage interest tax deduction, a gasoline tax and other measures, Moody’s said.

“In Moody’s view, a plan that would result in a reversal of the upward trajectory in the debt ratios would indeed be supportive of the country’s Aaa rating,” the ratings agency said in its report. “However, it is unlikely that the Commission’s recommendations will be adopted.”

-By Mark Brown and Nathalie Boschat, Dow Jones