Instead of forcing older Americans out of work, the severity of the nation’s economic slump is forcing many back into it.

Some have seen their pensions vanish. Others have seen the value of their homes plummet and their 401(k) balances cut in half.

Whatever the reason, since the recession started in December 2007, the number of employed workers over the age of 55 has actually grown by more than 800,000, according to figures released last week by the federal Bureau of Labor Statistics (BLS). By contrast, during the same period some 5.7 million workers have lost their jobs, and the unemployment rate now stands at 8.9 percent.

Human resources consultant Gayle Dudziak, 57, expected to retire at 60. But with the decline in her retirement portfolio and a child still in college, she figures she and her husband have no choice but to work until age 65. “My husband and I were just talking about this last night,” Dudziak said. “If I keep working for at least three more years, then I’ll be qualified for health benefits after 65.” Given the decline in the economy, “I don’t think we have much choice,” she said.

The trend of older Americans continuing to work “is very striking to us,” says Andrew Eschtruth of the Center for Retirement Research at Boston College. “With the financial crisis growing, more people seem to be clinging to their jobs in a way that we would not have seen a year or two ago.” People who would have retired are holding on, he said, while “others have decided to get back into the labor force because of their battered portfolios.”

While jobless levels have climbed markedly in the past 18 months, the BLS reported that the percentage of the workforce made up of people age 55 and over has risen from 17.9 percent to 19.2 percent, showing the resilience of older workers and their eagerness to keep working.

A survey released last month by the California Budget Project, a nonprofit research group, showed that older Californians are working longer than before. The study found that in 2008, 63 percent of people ages 55 to 64 were employed, up from 58 percent in 2000. In the two decades before that, the percentage hovered around 54 percent.

Only 22 percent of people ages 65 to 69 were still working in 2000, but the figure rose to 29.7 percent last year, an increase of 35 percent.

Experts cite other reasons for the fact that older workers are staying longer in the workforce. These include:

• The shift from defined-benefit to defined-contribution pension plans, which has increased the incentives to work later in life.

• Older Americans have less confidence that they can afford retirement. The 2008 Retirement Confidence Survey, released in April by the nonpartisan Employee Benefit Research Institute, found that “Americans’ confidence in their ability to afford a comfortable retirement has dropped to its lowest level in seven years.” Between 2007 and 2008 alone, the share of U.S. retirees who reported that they are “not too” or “not at all” confident that they have enough money to live comfortably throughout their retirement years increased from 21 percent to 34 percent.

• Changes in the Social Security program have created a financial incentive to continue working later into life. In 2000, for instance, Congress repealed a provision that had reduced the amount of Social Security benefits people ages 65 to 69 received if they had earnings from work above a certain threshold.

Some labor analysts argue that the rising tide of unemployment for young Americans, while older Americans continue to work, sows the seeds of future generational conflict.

A recent report on U.S. employment from 2000 to 2008 noted that the percentage of adults over age 55 who are working rose to 38 percent nationally from 32 percent, while youth unemployment steadily rose. “As a nation, we have taken the old adage ‘in with the new and out with the old’ and stood it on its head,” read the report, from Northeastern University’s Center for Labor Market Studies. “We have steadily increased the ranks of the employed with older workers and thrown the young out in the cold.”

Michael Zielenziger writes about the economy for AARP Bulletin Today.