The stock market has become America's main pension plan and savings bank, attracting funds from 48 percent of American households and becoming a key source of retirement savings, according to a comprehensive survey of investment patterns released yesterday.

Only 19 percent of American families held stocks or mutual fund shares in 1983, soon after the stock market began its extraordinary climb.

Perhaps because of the lengthy bull market, Americans have an abiding faith in the long-term potential of stocks. The survey found that nearly 9 out of 10 investors say they hold stocks for the long term, with most saying they care little about short-term fluctuations. Two-thirds of investors say they invest in the market primarily to help fund their retirement.

And, notwithstanding publicity about day traders and online stock trading, few investors trade actively.

The generation that spent most of its working years watching the bull market rise has become most enamored of stocks. Nearly half of all stock market investors are baby boomers (age 36 to 54), who increasingly view stocks and mutual funds as a critical part of their financial portfolio. And the most aggressive investors are members of Generation X (age 19 to 35), which has more of its assets in stocks and stock funds than any other generation.

"I saw the bull market. Like everybody else, I want to get rich," said Lydia Kupersmith, a 34-year-old attorney at the General Services Administration, explaining why she decided to jump into the stock market eight months ago, by joining a local investment club fancifully called the Metropolitan Millionaires Investment Club.

Joe Castelluccio, a 21-year-old senior at Georgetown University, said: "I think the effects of this bull market will never be undone. A whole slew of people are now too accustomed to investing in stocks." But, he added: "I'm not looking forward to my first bear market."

The study, based on interviews with 4,842 households in January and February, was released by the Investment Company Institute, which represents the mutual fund industry, and the Securities Industry Association, a trade group of financial services firms. The survey has a margin of error of plus or minus 2 percent.

The study attributed the rise in stock ownership to several factors -- the longest-ever bull market, the shift by companies to providing self-directed retirement plans -- such as 401(k) programs -- to employees, the increasing concern among baby boomers about their retirement, and efforts by financial companies to make investing easier and cheaper through things such as online trading and low minimums to open an account.

Financial advisers cite other factors as well. The gravity-defying resilience of the market, which has quickly bounced back stronger after every fall since 1982, has removed much of the fear factor.

"The perception that common stocks are risky is fading. The expectation issues have really gotten out of whack," said Dave Petersen, a financial adviser with Financial Services Advisory in Silver Spring. "Many people haven't saved during the first 30 years of their life and they are trying to use the market as a means to catch up."

The increasing use of stock options has also turned more employees into shareholders. "These employees were given the stocks. They didn't have a choice," said Gregory Sullivan, a financial adviser with Sullivan Bruyette, Speros & Blayney Inc. of McLean.

Frank Cowherd, a 56-year-old chemist in Charleston, W.Va., said many of the research scientists who work with him at Union Carbide Corp. are intensely interested in the markets because they own Carbide shares. "Some chart their stocks every day," he said.

The intense media focus on the markets has also helped educate Americans. Increasing numbers devour investment magazines, tune in to financial television networks such as CNBC and cruise the Internet for research reports, which has produced "a sea change in the comfort level in making stock investing decisions," Sullivan said.

Susan Scott, a 23-year-old administrative assistant in the District who has been investing for about a year with the help of a financial adviser, said the more she knows about the market, the less intimidating it is. "I can see the money I invested last year has not produced that much, but that doesn't worry me that much," Scott said.

According to the survey, stock market investors tend to be middle-aged with moderate incomes and assets. The typical investor is 47, has household income of $60,000 and household financial assets of $85,000. Most are married, employed and college graduates -- and 90 percent are white. Five percent of investors are African-American, 5 percent are Hispanic and 2 percent are Asian.

The amount of stock, held either individually or through mutual funds, varies widely. About 7 percent of households have equity assets of $500,000 or more, while 30 percent have less than $25,000. Stock market investors tend to have more of their assets in equities than any other investment vehicle.

Mutual funds are the preferred form of equity investment, particularly in retirement plans. Some 85 percent of investors own mutual funds that invest in stocks, and 54 percent own individual stocks -- but only 15 percent own only individual stocks. Nearly half of all investors own just mutual funds.

Most stockholders said they can tolerate risk to some degree -- nine percent were willing to take substantial risk for substantial gain; 31 percent were willing to take above-average risks; and 48 percent willing to take average risks.

Only 1 of 10 stock market investors conducted more than 12 transactions in 1998. In contrast, 55 percent did not conduct any stock trades last year. And Internet stock trading, although much talked about, is still in its "infancy," according to the study. Only 11 percent of investors executed trades over the Internet last year.

The Scope of Investing

Nearly half of all U.S. households invest in the stock market:

In stock market: 48.2%

Not in stock market: 51.8%

Of those who invest in the market, here is the share who own:

Only stock mutual funds: 47%

Both individual stocks and stock mutual funds: 38%

Only individual stocks: 15%

SOURCES: Investment Company Institute, Securities Industry Association