Invest for the long haul. Don’t try to play market swings.

Keep most of your money in stocks because they’ll beat the alternatives over time.

These are the rules that millions of individual investors accepted as gospel in the 1990s. But amid the worst stock market decline in a generation, and a severe crisis of confidence in the financial system itself, many investors are no longer sure they believe the old rules. It’s a shift with enormous implications if it gathers momentum.

With each drop in share prices which fell broadly again Friday some people even are questioning whether the once-unchallenged investing tenets were a sham to begin with, a conspiracy by powerful and greedy Wall Street and corporate interests to sucker Main Street into perhaps the biggest bubble in market history.

Listen to Les Greenberg, 59, a semiretired attorney and private investor in Culver City, Calif. “There’s the corporate elite and then there’s the rest of us, going to Versailles Palace and shocked by what we see. People are realizing that a game has been played in the financial markets.”

Or this posting from an investor on the Web site of mutual fund tracker Morningstar Inc.: “While riding from Los Angeles up the I-5 to Stockton, you pass a section where there are thousands of cows that will soon be slaughtered. It made me think of the millions of honest, hard-working people ‘investing’ for retirement in high-cost 401(k), 403(b) plans. Most of whom will most surely be financially slaughtered.”

Even some professional financial advisers are having second thoughts about repeating the mantra on stocks’ long-term superiority, and why investors should just stay put, despite their already massive losses.

“I don’t know that investors feel betrayed, but I’m sure there are a fair number that wish they didn’t believe what they have always read about investing being long-term,” said Margie Mullen, a fee-only financial planner with Mullen Advisory in Los Angeles. “Sometimes, I wish I didn’t either. I can name the people who called me a year ago, asking if they should get out of the market and I talked them out of it. In hindsight, I wish I hadn’t done that.”

Indeed, for many investors the market has worked to make a mockery of the idea of never selling stocks, especially in the case of the technology names that had been small investors’ favorites in the late 1990s. In 28 months, the tech-dominated Nasdaq composite index has sliced through four millennium marks, from 5,000 to 2,000.

All the way down, most Wall Street analysts exhorted investors to hold on, or to buy more. Now, at 1,319, Nasdaq is down more than 73 percent from its peak, the worst decline for a major market index since the Great Depression years.

To be sure, this flood of emotion and doubt is viewed by many Wall Street veterans as the strongest sign that the longest bear market since the 1940s is nearing an end. Historically, the market has often bottomed when the average investor’s mood is at its most dour.

But that argument has been heard for almost two months, and at various points in the past two years. Yet the market continues to slide. Stocks fell across the board again Friday, with the Dow Jones industrial average losing almost 400 points to just above 8,000, 4 percent for the week and the lowest since September. The broader Standard & Poor’s 500 index of blue-chip shares fell more than 33 points on Friday to a five-year low.

Even among investors who want to believe that stocks eventually will rebound, the risk that this time might be different or that the “long term” might be too long to wait is causing trepidation.

After the market crash of 1929, it took the Dow index until 1955 to get back to the ’29 peak.

Carlos Chavarria, a criminal lawyer in Los Angeles, said that in the last month he sold many of the stock investments he had held in retirement accounts and shifted that money into cash accounts.

“You like to think it’s for the long term, but you don’t want to break even in the long term,” said Chavarria, 45. In the past, he said, “people thought that (the market) was going to stall and dip a little, and then start going up again.” Now, he said, “I don’t think it’s going to happen for a long time.”

Chavarria said President Bush’s assurances about the economy’s stability have done little to bolster his confidence about making new stock purchases. “If it goes down, is he going to reimburse me?” he said.

The chilling reality for many buy-and-hold investors is that they have made almost no money in stocks for the past five years. That may not be the “long term” in the minds of financial advisers, but it’s long enough for some people with mortgages to pay, college expenses to meet and retirements to fund.

The return on the S&P 500 since mid-July 1997 works out to about 1.5 percent a year. An investor would have been far better off buying a five-year U.S. Treasury note in July 1997: That risk-free security would have paid 6 percent a year in interest since then.

“Our clients are not panicking, but they are getting tired,” said Judy Lau, a financial planner in Wilmington, Del. “This is different than 1987, when the correction was sharp, quick and over before you knew it. This is dragging on and on and on. The wall of regrets is getting very high.”

So Wall Street is holding its breath, fearing that Americans en masse will turn their backs on stocks not all at once, but during the next few years. That could severely limit investment capital available to U.S. companies. Yet amid the gloom, many investment advisers and individual investors insist that it makes no sense to give up on the idea of making money in stocks in the very long term. Buying stocks, after all, is buying a piece of the economy. If it grows, the market should too, over time.

The oft-quoted number is 10.7 percent: That’s the average annualized return on blue-chip stocks over the last 75 years, according to data firm Ibbotson Associates.

Despite the plunge of the past two years, the average annual return on blue-chip shares during the past 10 years is about 11.4 percent.

Stocks still may be overvalued today, analysts say, but even if the return during the next 20 years averages, say, 6 percent a year, it will beat the current returns on savings accounts and other safe havens.