WASHINGTON — The stock market's prolonged tumble has wiped out about $2 trillion in Americans' retirement savings in the last 15 months, a blow that could force workers to stay on the job longer than planned, tighten their wallets and possibly further stall an economy reliant on consumer spending, Congress's top budget analyst said Tuesday.

For many Americans, pensions and 401(k) plans are their only form of savings. The dwindling away of these assets — about a 20 percent decline overall — is another setback at a time when many consumers are grappling with higher gas and food prices, more credit card debt, declining home values and less access to loans.

"Unlike Wall Street executives, American families don't have a golden parachute to fall back on," said Rep. George Miller, D-Calif., chairman of the House Committee on Education and Labor. "It's clear that Americans' retirement security may be one of the greatest casualties of this financial crisis."

Even defined-benefit, or pension, plans, which are traditionally considered more stable, have been hit hard by the stock market's volatility, losing 15 percent of their assets over the past year, Peter Orszag, director of the Congressional Budget Office, told the House panel.

Despite the losses, companies will still be obligated to pay out the same pensions promised to employees but will have to recoup the extra costs in other ways, Orszag said. "When pension assets decline in 401(k) plans, the burden is on the workers," he said. "When pension plan assets decline in defined benefit plans, the burden is on the firm to make up the difference. The firm will have to pass those costs on to their workers, to their shareholders or to consumers."

Defined-benefit plans are company-sponsored programs that provide retirement payouts based on an employee's salary and tenure. The company shoulders the bulk of the investment decisions and risk. Defined-contribution plans, such as 401(k)s, turn those tasks over to the worker and are largely subject to the whims of the stock market.

Increasingly, employers have been switching workers into defined-contribution plans. The federal government has also pushed 401(k) plans heavily, approving a law late last year that makes it easier for employers to automatically enroll their employees in them and other similar retirement plans.

Defined-contribution plans tend to be more heavily weighted in stocks, either through individual holdings or mutual funds. As a result, said Orszag, "the value of assets in defined-contribution plans may have declined by slightly more than that of assets in defined-benefit plans."

For the first nine months of 2008, the percentage loss in average account balances among 401(k) participants was between 7.2 and 11.2 percent, according to the Employee Benefit Research Institute's analysis of more than 2 million plans.

Older employees between the ages of 56 and 65 who had the fewest years on the job were the least affected, while those 36 to 45 years old with the longest tenures suffered the steepest declines, said Jack VanDerhei, research director for the D.C.-based institute. Younger workers tend to have more stocks in their portfolios while older employees move toward safer investments such as bonds, VanDerhei explained.

The findings exacerbate a complaint among many workers and academics about 401(k) and similar plans that are so heavily tied to the stock market. Are they really the best retirement vehicles for workers?

"The loss of retirement security is a reversal of fortune and the result of very specific flawed governmental policies that have been biased toward 401(k) plans, rather than the result of technological change or the logical consequences of global economic trends," Teresa Ghilarducci, a professor of Economic Policy Analysis at the New School for Social Research, testified before the committee.

Other academics and analysts say 401(k) plans are beneficial to employees because they allow them to take control of their retirements.

Jerry Bramlett, president of consulting firm BenefitStreet, said 401(k) participants should resist the urge to pull money out of stocks because that would only lock in their losses.

"Markets do go up and down and 401(k) participants must try to remember to think long-term," he said.

Many investors have been buying low-yielding Treasury bills in recent months because they are considered less volatile. Bramlett cautioned against that because it would leave them vulnerable to inflation.

That said, 401(k) participants should evaluate their portfolios to make sure their money is spread out among both stock and fixed-income investments. They should also make sure they do not have too much of their own company's stock.

Public pensions also have suffered. The assets held by state and local governments' pension plans declined by more than $300 billion between the second quarter of 2007 and the second quarter of 2008, according to the Federal Reserve. About 60 percent of public pension funds are invested in stocks, 30 percent in domestic fixed-income securities, 5 percent in real estate, and the remaining 5 percent in other products.

Miller called the findings "very cataclysmic for middle-class families."

Several analysts who testified at the hearing said the most vulnerable workers are those nearing retirement, who have large balances in their retirement plans that are now shrinking. Tighter home budgets are also crimping workers' retirement savings. According to a survey released yesterday by AARP, 20 percent of baby boomers stopped contributing to their retirement plans in the past year because they have had trouble making ends meet.

Already, more workers are delaying retirement, a trend that analysts and economists expect to accelerate thanks to the state of the economy. The fraction of people age 55 and older who work full time grew from about 22 percent in 1990 to nearly 30 percent in 2007, according to the Bureau of Labor Statistics.

By 2016, the bureau predicts, the number of workers age 65 and over will soar by more than 80 percent, and they will make up 6.1 percent of the total labor force. In 2006, they accounted for 3.6 percent of active workers.