The third quarter in the stock market was a disaster for investors who had to sell. Almost every market average and category took a drubbing. Only oil, gas and gold stocks were major exceptions.

The Dow Jones industrial average, the Standard & Poor's 500-stock index and stock mutual funds, lost 15 percent of their value, but averages for smaller stocks fared worse. The over-the-counter composite index plunged 25 percent.Those who tend to invest in certain categories of stocks might have done much worse. Among New York Stock Exchange listings, apparels lost 32 percent, textiles 31 percent, electronics 29 percent and automotives 27 percent.

Some small-company shares lost more than half their value during the three months of July, August and September. It wasn't very unusual to see over-the-counter stocks with one-day declines of 25 percent in a single day.

In some instances, professional pickers did as poorly as amateurs. Many stock mutual funds lost more than 30 percent of their value during the three months; that is, they performed worse than dart-throwers.

The statistical evidence is indeed a picture of disaster, but as Chinese philosophers, inspirational teachers, evangelists and some smart investors try to explain, disaster may also spell opportunity.

"Stock prices have now declined to the point where above-average long-term investment returns can once again be expected," says Wright Investors, a large portfolio management and advisory company that stresses the long term.

For old investors who were forced to sell, the bad news is bad indeed, but for new investors the bad news is good news, a two-for-one promotion, a discount sale the like of which no marketing executive ever imagined.

It doesn't come without risk, of course, because the stock market could fall even lower before the bear market ends. And the sad fact is that the eventual rise in the market is likely to be slower than its earlier fall.

Nevertheless, this is the type of market in which patient investors who stress fundamental values and maintain long-term perspectives make lots of money. It has been demonstrated again and again, but forgotten as often.

The long term is stressed, for example, by investment clubs that make up a large percentage of membership in the National Association of Investment Clubs. The ups and downs of the economy don't matter to them; they go right on buying.

As a result, they automatically exploit economic dips and stock market declines. When the market is high, they might have to pay $10 a share, but when it falls they might get two shares for what used to be the price of one.

The assumption they make, of course, is that the general tendency of the U.S. economy is to expand, and the general direction of stocks, which reflect that economy, is to rise. They buy and wait and profit.

Some do, anyway. In spite of the professions of optimism and patience, many individuals and investment clubs lose faith when the market falls. They fail to perceive opportunity. NAIC records show many clubs dissolve.

It isn't easy to see beauty in the debris of a bull market, or view it as a two-for-one sale. They might buy toothpaste that way, but not stocks.