Failure of the Penn Square National Bank of Oklahoma, the fourth biggest bank bust in U.S. history, has triggered losses among the 177 credit unions and savings and loan associations that greedily had responded to Penn Square's promise of extra-generous interest payments--up to 2 full percentage points over normal--for uninsured deposits.

It has also shaken faith in the banking system, and raised questions about the good judgment of some of the nation's largest and presumably most sophisticated banks.

The Penn Square disaster was the 22nd commercial bank failure so far this year and, of course, the biggest. It ensnared, as well, the Chase Manhattan Bank, the Continental Illinois Corp., the Seattle National Bank, and the Northern Trust Co. They bought $2 billion worth of what turned out to be bad-- that is, undercollateralized--energy loans from Penn Square. Continental alone plunged for $1 billion worth.

"Are there other Penn Squares out there?" I asked a knowledgeable Wall Street financial man. "Oh, sure," he said without a moment's hesitation. "The only word for it is scary."

In fact, federal regulators--whose judgment in the Penn Square debacle will be questioned in a congressional investigation--now list 269 "problem banks" that show various degrees of shakiness. Another element in the general concern over a weak national financial structure is the fact that there have been 12,000 corporate bankruptcies recorded in the first six months of 1982, or twice recent annual totals.

Perhaps the most stunning aspect of the Penn Square story is that federal regulators have known for some time that the big Southwest institution was getting in over its head. As far back as February 1980, the Comptroller of the Currency (regulator of national banks) flagged Penn Square as a troubled institution. But no one took effective action to force Penn Square to shape up.

In the final several days preceding the closure of the bank on July 6, some Federal Reserve officials argued that the shock of the failure of a bank as large as Penn Square would be so great that the bank should be merged into another institution, instead of being put into receivership.

That would have been an elaborate "cover-up," making good the losses of any depositor, even over the $100,000- insurance level. In effect, the taxpayers would have been stuck with the cost of the vast indiscretions of the Penn Square management--and those of the other banks--instead of just sharing it.

But the Comptroller of the Currency and the Federal Deposit Insurance Corp. prevailed in the view that no one could put a price tag on the total liabilities Penn Square might face in claims from the banks to which it had sold loans.

So they closed Penn Square's doors, and are now in the process of liquidating it, paying off those depositors with $100,000 or less. In the end, the FDIC will share the ultimate losses with all uninsured depositors and creditors. The bank held about $190 million worth of uninsured deposits, including some by municipalities and wealthy individuals.

A fascinating twist is the unbelievable irresponsibility of those managers of other people's money, who were willing to place deposits in an uninsured status in Penn Square for an extra return--at a time when conservative investors take a lower return in exchange for quality.

"If somebody offers you a half-point yield over the market, you might look at it," says an investment broker. "But if someone offers you two full points, you know damn well that something's wrong." Credit union and S&L managers who were willing to play this kind of financial Russian roulette deserve to be fired, if not jailed.

Major banks like Chase Manhattan and Continental, which ought to know better, will not only lose dollars in their search for a fast buck in the energy business, but suffer loss of prestige and erosion of their reputations.

"How can such well-known banks be so casual about the way they put their money out?" I asked an adviser to equally famous banking and other institutions.

"Because they have so much of it," was his candid answer. "The remarkable thing is that the system works as well as it does." Adds an ex-regulator: "One of the problems is that bankers trust bankers. If one bank is offered a participation by another, they don't look at it closely enough."

Thus, there is a time bomb ticking away in financial markets: many of the "assets" listed on the plus side of commercial banks' assets sheets are worthless loans--and not just for energy development. You can bet more will surface before we get out of this mess.