In 1983, after a deep recession, women in that range made up only 7 percent of those who had been out of work for six months or longer, according to the Labor Department. Last year, they made up 14 percent.

Twice, Ms. Eisen exhausted her unemployment benefits before her check was restored by a federal extension. Last week, her check ran out again. She and her husband now settle their bills with only his $1,595 monthly disability check. The rent on their apartment is $1,380.

“We’re looking at the very real possibility of being homeless,” she said.

Every downturn pushes some people out of the middle class before the economy resumes expanding. Most recover. Many prosper. But some economists worry that this time could be different. An unusual constellation of forces  some embedded in the modern-day economy, others unique to this wrenching recession  might make it especially difficult for those out of work to find their way back to their middle-class lives.

Labor experts say the economy needs 100,000 new jobs a month just to absorb entrants to the labor force. With more than 15 million people officially jobless, even a vigorous recovery is likely to leave an enormous number out of work for years.

Some labor experts note that severe economic downturns are generally followed by powerful expansions, suggesting that aggressive hiring will soon resume. But doubts remain about whether such hiring can last long enough to absorb anywhere close to the millions of unemployed.

A New Scarcity of Jobs

Some labor experts say the basic functioning of the American economy has changed in ways that make jobs scarce  particularly for older, less-educated people like Ms. Eisen, who has only a high school diploma.

Large companies are increasingly owned by institutional investors who crave swift profits, a feat often achieved by cutting payroll. The declining influence of unions has made it easier for employers to shift work to part-time and temporary employees. Factory work and even white-collar jobs have moved in recent years to low-cost countries in Asia and Latin America. Automation has helped manufacturing cut 5.6 million jobs since 2000  the sort of jobs that once provided lower-skilled workers with middle-class paychecks.