To be sure, there were few ready remedies. Some critics argue that the United States could have pushed Beijing harder to abandon its policy of keeping the value of its currency weak  a policy that made its exports less expensive and helped turn it into the world’s leading manufacturing power. If China had allowed its currency to float according to market demand in the past decade, its export growth probably would have moderated. And it would not have acquired the same vast hoard of dollars to invest abroad.

Others say the Federal Reserve and the Treasury Department should have seen the Chinese lending for what it was: a giant stimulus to the American economy, not unlike interest rate cuts by the Fed. These critics say the Fed under Alan Greenspan contributed to the creation of the housing bubble by leaving interest rates too low for too long, even as Chinese investment further stoked an easy-money economy. The Fed should have cut interest rates less in the middle of this decade, they say, and started raising them sooner, to help reduce speculation in real estate.

Today, with the wreckage around him, Mr. Bernanke said he regretted that more was not done to regulate financial institutions and mortgage providers, which might have prevented the flood of investment, including that from China, from being so badly used. But the Fed’s role in regulation is limited to banks. And stricter regulation by itself would not have been enough, he insisted.

“Achieving a better balance of international capital flows early on could have significantly reduced the risks to the financial system,” Mr. Bernanke said in an interview in his office overlooking the Washington Mall.

“However,” he continued, “this could only have been done through international cooperation, not by the United States alone. The problem was recognized, but sufficient international cooperation was not forthcoming.”

The inaction was because of a range of factors, political and economic. By the yardsticks that appeared to matter most  prosperity and growth  the relationship between China and the United States also seemed to be paying off for both countries. Neither had a strong incentive to break an addiction: China to strong export growth and financial stability; the United States to cheap imports and low-cost foreign loans.

In Washington, China was treated as a threat by some people, but mostly because it lured away manufacturing jobs. Others argued that China’s heavy lending to this country was risky because Chinese leaders could decide to withdraw money at a moment’s notice, creating a panicky run on the dollar.