WASHINGTON (AP) -- Whether or not the government is actually on the verge of taking over mortgage finance companies Fannie Mae and Freddie Mac, investor fears that a bailout is imminent could turn such a worst-case scenario into reality.

Amid renewed concern that shareholders will wind up with nothing if the government intervenes to bail out the troubled companies, shares in the mortgage finance giants tumbled Monday to the lowest levels in nearly two decades.

Fannie Mae's stock slid more than 22 percent, or $1.76, to $6.15 on Monday, while shares of Freddie Mac fell 25 percent, or $1.46, to $4.39.

"Some of these things become self-fulfilling prophecies because market confidence is so fragile," said Karen Shaw Petrou, managing partner of consulting firm Federal Financial Analytics in Washington.

However, a more likely scenario, analysts say, would stop short of nationalizing the two companies and would take the form of emergency loans to Fannie and Freddie from the Federal Reserve or Treasury Department.

The Treasury Department late last month gained the authority to boost Fannie and Freddie through an investment or a loan should the companies need their finances propped up due to soaring losses from bad mortgages.

The new government power, enacted by Congress after the companies shares plunged to levels not seen

The typical American retires at age 63. Those fortunate few who have traditional pensions, retiree health insurance, and a fully loaded 401(k) will probably be fine. But if you haven't saved enough to fund 30 years of retirement--and most baby boomers aren't even close--the obvious solution is working longer. (The other possible solution is to reduce your standard of living). But how much longer will boomers need to work to finance a secure retirement?

"For those workers who can work, the way to a secure retirement is to keep working until 66," says Alicia Munnell, director of the Center for Retirement Research at Boston College and coauthor of Working Longer: The Solution to the Retirement Income Challenge. Social Security currently replaces 39 percent of preretirement income for the average earner retiring at age 65 after the Medicare Part B premium is automatically deducted. But those who retire at the same age in 2030 can expect Social Security to replace only 30 percent of earnings, according to Munnell's calculations. "Retirees in 2030 will have to work two to four years longer to maintain today's level of replacement income," she says.

It turns out that Munnell's estimate is a conservative one. Marc Freedman, founder and CEO of the think tank Civic Ventures and author of the book Encore: Finding Work That Matters in the Second Half of Life, says that boomers should try to work until at least age 70. The share of households prepared for retirement would nearly double from 31 to 60 percent if early boomers currently between the ages of 54 and 63 delayed retirement from age 65 to 70, according to a McKinsey & Co. analysis. And Tamara Erickson, author of Retire Retirement: Career Strategies for the Boomer Generation, says baby boomers