Uncle Sam isn’t in danger of losing his top credit rating, but he’s not in the greatest shape, either.

So says Moody’s Investors Service in its quarterly assessment of triple-A-rated countries.

Paying the interest on their debt remains manageable for these countries, Moody’s says, so their governments aren’t in any immediate danger of a downgrade.

But among the AAA countries, the U.S. and the U.K. are “most stretched” by their debt obligations, Moody’s says.

The debt ratings are important because a downgrade raises a country’s borrowing costs. And virtually every big country faces a difficult challenge in removing bailout and stimulus money quickly enough to avoid inflation and slowly enough to keep the weak recovery going.

“This exposes governments to substantial execution risk in the implementation of their exit strategies, which could yet make their credit more vulnerable,” says Arnaud Mares, senior vice president in Moody’s sovereign risk group and the main author of the report.