The United States isn't in jeopardy of losing its gold-plated credit rating, though by one measure America is closer to the ratings-downgrade danger zone than Spain.

That's according to credit rating agency Moody's. In a quarterly report about sovereign debt, Moody's analysts wrote that despite market worries about rising government debt levels, there is "no imminent rating pressure" for the United States and other big governments carrying its highest triple-A rating.

But the report added that these governments' margin for error "has in all cases substantially diminished," thanks to a weak outlook for economic growth and enormous debt loads taken on to quell the financial meltdown of 2008-2009.

Cutting back on public spending too soon risks a double-dip recession, Moody's said, while leaving stimulus measures in place too long could lead to a sharp rise in interest rates "with more abrupt rating consequences a possibility."

What's more, governments that wish to avoid credit downgrades may need to implement harsh and potentially unpopular policies. The Moody's analysts, led by London-based managing director Pierre Cailleteau, wrote that "preserving debt affordability ... will invariably require fiscal adjustments of a magnitude that, in some cases, will test social cohesion."

Nor can big developed countries expect to export their way to health on the back of booms in emerging markets such as India and China. "Demand from the emerging world undoubtedly provides some support, but cannot on its own compensate for weak domestic demand," Moody's said.

In the case of the United States, interest payments on general government debt -- combining the federal government with the states -- could rise above 10% of revenue by 2013, according to the report.

That's the level at which the rating agency typically considers a downgrade. Moody's said debt affordability is the key factor to consider in ratings decisions, because debt costs are apt to constrain policymakers.