No matter how much economists and political leaders warned about huge global trade imbalances and the astronomical foreign debt of the United States, American consumers kept buying more and borrowing more from the rest of the world.

Until the financial crisis, that is.

In a striking case of shock therapy, global trade imbalances have declined by almost half since the financial system nearly collapsed one year ago.

On Friday, the Commerce Department reported that the trade deficit of the United States shrank by another $1.2 billion in August, to $30.7 billion. American exports edged up to $128.2 billion and imports declined slightly to $158.9 billion.

But the real news is the change from one year ago.

For the first eight months of the year, the United States trade deficit with China is down by about 14 percent or $20 billion, compared with one year ago. The nation’s trade deficit with Japan has shrunk by almost 20 percent, and its deficits with Mexico, Canada and the European Union are down more than 40 percent.

The huge shift stems mainly from the staggering collapse in trade. With credit markets frozen and Americans facing the highest unemployment in more than 30 years, the United States suddenly stopped shopping overseas at anywhere near the volumes that had become normal.

And even though the economy is beginning to recover, economists say the global trade shift still has some distance to go. The value of the dollar, which has been falling sharply, will make imports more expensive and restrain American appetites for at least the next year.

All of which raises a question: is the free market suddenly imposing the kind of brutal rebalancing that global political leaders, for all their pronouncements and handwringing, never came close to achieving?

Last month, President Obama and leaders from the Group of 20 large economies agreed to cooperate on reducing global imbalances. The United States would try to increase saving and get its fiscal house in order. China and other export-dependent countries would try to save less and spend more at home. The leaders even agreed to submit to evaluation of each other’s policies, with help from the International Monetary Fund.

At least for the moment, the financial crisis has delivered swifter and more sweeping change than policy makers could hope to accomplish.

It isn’t just in the United States, either. China’s trade surplus with the rest of the world has plummeted to less than 6 percent of its gross domestic product, from 11 percent.

But economists say the change could prove fleeting.

“Officials cannot just sit there and do nothing, and expect the rebalancing to continue,” said C. Fred Bergsten, director of the Peterson Institute for International Economics.

Indeed, American consumers are already showing hints of their old fondness for shopping rather than saving. The household saving rate shot up from less than 1 percent before the crisis to more than 5 percent this spring, but it has since slipped back to less than 4 percent. In the early 1990s, American families were saving about 7 percent of their income — and even that was less than in much of Asia and Europe.

Simon Johnson, a professor of economics at the Massachusetts Institute of Technology, said it was normal for a country’s trade balance to improve during an economic downturn. “The adjustment we’re seeing right now could be the harbinger of a real adjustment in saving and spending, but we don’t know yet,” Mr. Johnson said. “People in emerging markets want to run big surpluses, because they want to build up reserves.”…

www.nytimes.com