The immediate danger, economists say, are countries in Eastern and Central Europe, like Bulgaria and Estonia, which run steep trade deficits and are vulnerable to a sudden flight of foreign capital.

Iceland, with an overheated economy and suffocating foreign debt, may prove to be the first national casualty of the crisis. On Monday, threatened by a wholesale financial collapse, the government in Reykjavik assumed sweeping powers to intervene in its banking industry.

“We were faced with the real possibility that the national economy would be sucked into the global banking swell and end in national bankruptcy,” Prime Minister Geir H. Haarde said on Monday.

The crisis that began as a made-in-America subprime lending problem and radiated across the world is now circling back home, where it pummeled stock and credit markets on Monday.

But with global growth slowing sharply, the problems could spread to larger emerging markets, even China, which has a hefty current account surplus and immense foreign reserves.

“Where is China going to sell its exports?” Mr. Johnson of M.I.T. said. “Everyone is going into recession at the same time.”

This week, the focus will be on the Group of 7, whose finance ministers and central bankers are scheduled to meet on Friday at the Treasury Department. The group issued a perfunctory statement of support for the United States, after the Treasury secretary, Henry M. Paulson Jr., briefed members about the rescue plan in a conference call two weeks ago.

But European finance ministers, notably Peer Steinbrück of Germany, noted that the crisis began in the United States, and played down the need for a systemic European response.

Mr. Zoellick, in his speech, said flatly that the Group of 7 “is not working.” He advocates expanding the group — which includes the United States, Canada, Britain, Italy, France, Germany and Japan — to include emerging economies like Brazil, China, India and Saudi Arabia.

The urgency of the moment, experts said, demands a bolder response from the Group of 7. Mr. Bergsten said the group should commit to a coordinated stimulus plan to stave off a recession.

“Just as the U.S. rescue plan may not be enough,” he said, “a U.S. stimulus plan by itself will not be enough.”

Indeed, the ripple effects from Europe and the United States were amplified as they spread to stock markets in Russia, Brazil, Indonesia and the Middle East.

These countries had little to do with the subprime crisis but were vulnerable to a sudden halt in the flow of money. They lack even the veneer of national or regional cooperation that protects Europe and the United States. Stock markets in emerging economies recorded their worst one-day decline in 21 years on Monday, with trading in Russia and Brazil halted to stem an investor panic.

"It looks pretty ugly down the road," said Simon Johnson, an economist at the Massachusetts Institute of Technology and a former chief economist of the International Monetary Fund who specializes in financial crises. "Everybody is going to get caught up in this."

The global nature of the crisis and its growing collateral damage ought to galvanize countries to work together to fashion a concerted response, Johnson said. There is a chance to do that this week, with dozens of finance ministers and central bankers converging on Washington for the annual meetings of the IMF and the World Bank.

The trouble is, these institutions no longer have the resources or authority to lead such an effort. The IMF, which played a central role in the Asian crisis, has been relegated to the sidelines this time its credibility tarnished by that episode and its skills ill-suited to a crisis in advanced economies. These days, it mainly issues lonely warnings about the impact on developing countries.

That is particularly true in Europe, which has an effective central bank but lacks a unified legislature or treasury to coordinate or finance a rescue of the banking system. So far, economists say, Europe's response to the crisis in its banks has been mostly marked by denial and dissension.

From London to Berlin, governments are clinging to a piecemeal approach. The British and the Germans have resisted a broader solution, because they fear they will end up rescuing their neighbors.

A weekend meeting of European leaders in Paris, called by President Nicolas Sarkozy, ended with a pledge that Europe would not countenance a bank failure like that of Lehman Brothers, but little else.

Part of the problem, experts said, is the nature of this crisis: bailouts of banks are costly and unpopular with taxpayers — even more so, as in Europe, where burden sharing is a perennial sore point.

"Taxpayers won't agree to bail out the banking system of other countries," said Thomas Mayer, the chief European economist at Deutsche Bank in London. "Not even in Europe, where you have a neutral framework, could you get people to cooperate on a joint effort."