As government data revealed that 651,000 more jobs disappeared in February, a sense took hold that growing joblessness may reflect a wrenching restructuring of the American economy.

The unemployment rate surged to 8.1 percent, from 7.6 percent in January, its highest level in a quarter-century. In key industries — manufacturing, financial services and retail — layoffs have accelerated so quickly in recent months as to suggest that many companies are abandoning whole areas of business.

“These jobs aren’t coming back,” said John E. Silvia, chief economist at Wachovia in Charlotte, N.C. “A lot of production either isn’t going to happen at all, or it’s going to happen somewhere other than the United States. There are going to be fewer stores, fewer factories, fewer financial services operations. Firms are making strategic decisions that they don’t want to be in their businesses.”

This dynamic has proved true in past recessions as well, with fading industries pushed to the brink during downturns before others emerged to create jobs when economic growth inevitably resumed. But with job losses so enormous over such a short period of time, some economists argue that the latest crisis challenges the traditional American response to hard times.

For decades, the government has reacted to downturns by handing out temporary unemployment insurance checks, relying upon the resumption of economic growth to restore the jobs lost. This time, the government needs to place a greater emphasis on retraining workers for other careers, these economists say.

....Since the recession began, the economy has eliminated a net total of roughly 4.4 million jobs, with more than half of those positions — some 2.6 million — disappearing in the last four months alone. This rapid deterioration has prompted talk that some industries are being partly dismantled. Layoffs are multiplying because of dysfunction in the financial system, which is prompting even healthy companies to shed workers and shut down operations out of concern they may soon lose access to credit.