Together, those developments underscore that even as Europe’s debt turmoil enters its third year, no clear solutions are yet in sight — despite recent signs that a new lending program by the European Central Bank might be easing financial market pressures.

S.& P. warned in December that it might downgrade many of the 17 nations that share the euro, largely because it said European politicians were moving too slowly to strengthen the monetary union and because the euro zone’s problems were propelling Europe toward its second recession in three years.
European politicians, in turn, criticized S.& P.’s downgrade plans as providing no meaningful new information to investors but simply stoking a sense of crisis.

To some extent, the prospect of rating downgrades has already been priced into recent bond auctions by Italy, Spain and other countries. Italy, in fact, completed another fairly successful bond auction on Friday, even as rumors of the downgrades had begun to swirl.

But the downgrades may now add to the borrowing costs of the nations affected. Some commercial banks that are required to hold only the highest-rated government securities will have to replace French bonds with other assets, like bonds of Germany.
And the downgrades cannot help but add to the gloom pervading Europe’s economic climate.

“Today’s rating actions are primarily driven by our assessment that the policy initiatives that have been taken by European policy makers in recent weeks may be insufficient to fully address ongoing systemic stresses in the euro zone,” S.&. P said.
Finance Minister François Baroin of France said Friday that the loss of his country’s pristine AAA rating, cut a notch to AA+, was “not good news” but was “not a catastrophe.” He insisted that the country was headed in the right direction and that no ratings agency would dictate the policies of France, which has Europe’s second-biggest economy, behind Germany’s.

But the downgrades pose fresh challenges for Europe’s political leaders, particularly President Nicolas Sarkozy of France, who is expected to run for re-election this spring and had long cited his country’s AAA credit rating as a badge of honor.

In August, when S.& P. cut the United States a notch from its top-rank AAA rating, markets briefly plunged. But bond investors have continued to flock to the debt of the United States, which as the world’s largest economy has retained the perception of a financial safe haven. That has kept the United States government’s interest rates at very low levels. But none of the countries downgraded on Friday can necessarily count on such a reaction.

After Friday, the only euro zone nations retaining their top AAA ratings are Germany, the Netherlands, Finland and Luxembourg.
Italy and Spain, which are considered the two big euro-zone economies most vulnerable to an escalation of debt problems, both were downgraded two notches, Italy to BBB+ and Spain to A.
“It will make it harder to erect firewalls around struggling euro zone economies and convince investors that things are more sustainable,” said Simon Tilford, the chief economist for the Center for European Reform in London.

Stocks were down broadly if not deeply in Europe and the United States on Friday, as rumors of the downgrades preceded S.& P.’s announcement, which came after the close of trading on Wall Street. And the euro fell to a 16-month low against the dollar.
Just as significant as the ratings downgrades may be the suspension on Friday of the creditor talks in Greece — whose debt S.& P. long ago gave junk status.

In October, the European Union pledged to write off 100 billion euros ($127.8 billion) of Greece’s debt if bondholders would agree to voluntarily accept 50 percent losses on their Greek holdings. Such an arrangement, known as private-sector involvement, or P.S.I., has been pushed by Chancellor Angela Merkel of Germany as a way of forcing banks, not only European taxpayers, to foot the bill for bailing out Greece.
But talks broke down on Friday between Greece and the commercial banks.