Mr. Heebner’s funds have not avoided the carnage this year. The CGM Focus fund is down about 42 percent so far in 2008. But his long-term track record is impressive. In the decade that ended Dec. 31, 2007, CGM Focus rose 26 percent a year, including reinvested dividends, making it among the best-performing mutual funds.

Mr. Heebner is not alone in his optimism.

“I think in years to come  I wouldn’t say months to come  we will perceive this as being a great value-buying opportunity,” said David P. Stowell, a finance professor at Northwestern and a former managing director at JPMorgan Chase. “Two and three years from now, it will seem very smart.”

Image Martin Whitman, manager of the Third Avenue Value fund. Credit... Ruby Washington/The New York Times

Even before their jaw-dropping plunge of the last month, stocks were not expensive by historical standards, based on fundamentals like earnings and cash flow. Now, after falling 30 percent or more since early September, stocks in stalwart, profitable corporations like Nokia, Exxon Mobil and Boeing are trading at nine times their annual profits per share or less. Many smaller companies are even cheaper. Some of those stocks are trading at five times earnings or less.

Those ratios are historically low. Over all, the Standard & Poor’s 500-stock index is trading at about 13 times its expected profits for 2009, its lowest level in decades. In contrast, at the height of the technology bubble in early 2000, the stocks in the S.& P. traded at about 30 times earnings, the highest level ever. At the same time, the 10-year Treasury bond paid about 6 percent interest, compared with less than 4 percent today.

Investors have fled stocks in favor of government bonds, insured bank deposits and other low-risk investments because they are deeply afraid of the worldwide economic crisis, said Stephen Haber, an economic historian and senior fellow at the Hoover Institution. But he said he believed that fear might have gone too far.

“If there is good and wise policy, and government moves effectively, this need not play itself out in ways like the Great Depression, which is the image that is playing itself out in people’s mind,” Mr. Haber said. Government action typically does not work immediately, and banking crises around the world often require multiple interventions, he said.