Nonetheless, a little-noticed study the Labor Department released several months ago found that the benefits of the biggest federal job training program were “small or nonexistent” for laid-off workers. It showed little difference in earnings and the chances of being rehired between laid-off people who had been retrained and those who had not.

In interviews, the authors of the study and other economists cited several reasons that retraining might not be effective. Many workers who have lost their jobs are older and had spent their lives working in one industry. In need of a job right away, many pick relatively short training programs, which often have marginal benefits. Job retraining is also ineffective without job creation, a point made by several economists who have long cautioned against placing too much stock in it. Finally, workers trying to pick a new field cannot predict the future of the labor market, especially in a time of economic upheaval.

“I can’t tell you with any degree of certainty, and I’ve been doing it for 20 years, what the hot jobs are going to be,” said one of the authors, Kenneth R. Troske, an economics professor at the University of Kentucky.

An examination by The New York Times of one group of laid-off workers  36 people who finished their retraining at Macomb Community College just outside Detroit at about the same time as Mr. Hutchins, from May to August 2008  found that at least 60 percent appeared either not to be working or to be in jobs unrelated to their training.

Several had jobs but then lost them later, according to state wage records and interviews. And a review of wages for several employed workers before and after training showed that almost all had lost ground.