John M. Templeton, the premier global investor of the past half-century, has a stunning new secret he is willing to share.

After decades of surprising his colleagues by putting his money in countries they had never even considered as investment targets, Templeton has come up with what may be his most startling discovery of all.Most of the world's best investment bargains right now, he confides, are in a neglected little place known as the United States of America.

And Templeton, as usual, is putting his (very big) money where his (very modest) mouth is. Only once before, in the 1960s, did the soft-spoken, Tennessee-born wizard have as much as half his funds in a single country. That was Japan, and his holdings then soared so dramatically that he long since has sold all his Japanese investments, on the ground that there are now far better bargains elsewhere.

Today, at a time when American markets are jittery and investors can't shake the memory of the sharp correction in 1987, Templeton has put an unprecedented 65 percent of the $12 billion he manages (in the Templeton Funds and elsewhere) into U.S. stocks. And he is waiting, with his customary patience and acumen, for a massive payoff.

"Fourteen months after the crash, it would be hard to say that we have not already started a bull market," he told me. "I would think it's still an even chance that we will reach 3,000 on the Dow Jones industrial average by the end of 1990."

Super-optimistic? Maybe. But those with long memories will recall how absurd many thought it when Templeton first told me, early in this decade, that the Dow would approach 3,000. At the time, the prevailing wisdom, as expressed by one of the overpublicized gurus of the day, was that a mere 1,000 would represent the market's permanent "graveyard in the sky."

Templeton, his verve clearly undiminished at the age of 76, is now setting his sights considerably loftier. Stocks in the 1990s will go "higher than almost anyone expects," he believes. "By the time the next bull market gets roaring, earnings should be 40 percent higher than now. That would justify share prices 40 percent higher than the previous peak. That would be over 4,000 on the Dow.

"The last bull market carried share prices to triple where they had been. Triple the low point for this one, would carry them to 5,100. Also, the shortage of shares that has developed through mergers and corporations buying back their own stock might carry prices higher than that. So I would say that by the time that this bull market reaches its peak, there's a 50-50 chance the Dow will be above 5,000."

All that unconventional enthusiasm has caused Templeton to position himself and the substantial funds he manages for what he sees as another brilliant decade for common stocks. And while he told me he still finds bargains elsewhere in the world - notably in New Zealand, Hong Kong, Canada and Britain - he is making by far his heaviest bet on Wall Street.

Which stocks? Well, Templeton says, characteristically, that he is finding his best American bargains "in those things that are depressed. You have to buy those things that are unpopular."

"Unpopular" areas that rank high on his current list include the financial stocks, particularly those (such as Merrill Lynch) that sponsor mutual funds; life insurance stocks (such as Cigna); bank stocks (such as National Bank of Canada), and the long-neglected "emerging growth stocks" (such as Standard Pacific).

Two cautions are appropriate. The first is the usual one: Even a proven investment genius like John Templeton does not bat 1000. The second is a word to the unwary: This man does not give "hot tips"; his average holding time for a stock is five years.

But it is just such uncommon patience that has enabled Templeton to compile what is, quite simply, the single best long-time public record in investing. His philosophy is to seek out the world's best bargains and then to sit with them until the crowd comes along. And it is not the worst news of the year that John Templeton now believes that most of the world's best bargains can be found in our own backyard.