The average congressman looks down his nose at the International Monetary Fund and the World Bank. With all the troubles he's got in his own district, he asks himself, why should he worry about the international monetary system?

Sen. Charles Mathias (R-Md.), who has been trying to give a gentle nudge to congressional authorizations for expanded American support of the IMF, tells me that the first question he's asked by his colleagues on the Hill is:

"Why should I vote $10 billion to bail out Citicorp or the Chase Manhattan Bank when I've got plenty of troubles in my own district?"

This instinctive, if shortsighted view is understandable, especially at a time of recession. Many of our nation's biggest and presumably most conservative and smartest bankers were shooting craps with their stockholders' money --in effect betting that inflation would continue forever

Yet, as Mathias and others have observed, the harsh reality is that if the banks--and it's not just Chase Manhattan and Citicorp, but up to 1,500 smaller ones participating in these loans--don't get some indirect support, the unemployment level in the United States could go up instead of down as one Third World nation after another goes belly-up.

"Just as it is the worst form of false economy to cut the household budget by (cutting down on) fire insurance, it would be seriously misguided to economize by failing to maintain adequate international fire insurance," William R. Cline, senior fellow at the International Institute for Economics, testifed before Mathias' Foreign Relations subcommittee.

Moreover, in recognition of the fact that the banks share some of the responsibility for the current mess, the IMF is now requiring, as a condition of extending new loans to debtor countries, that the commercial banks increase their own loans.

Thus, Citicorp and Chase Manhattan--to use Congress' favorite surrogate symbols for greedy bankers--are now faced with the choice of putting new money in or watching their customers default on their old loans.

Nonetheless, there is every indication that the Reagan administration will encounter stiff opposition in picking up its share of the new IMF capitalization, even though no budget outlay is involved. There is merely a paper transaction in which the United States transfers dollars to the IMF, and gets an equal and offsetting international deposit on the books of the IMF.

Failure to act, as a group of distinguished former financial officials including ex-Federal Reserve Board Chairman William McC. Martin are saying, could mean that "the debtor nations (fall) into what might prove to be a bottomless pit of international bankruptcy."

But it is also clear that even if we all escape a brush with disaster this time, some basic changes must be made.

First of all, the Walter Wriston (Citicorp) philosophy that no sovereign nation can go bankrupt, and that therefore there should be no restraints on the amount of money a bank can lend to a government, needs to be placed where it firmly belongs, on the garbage heap. That attitude has encouraged borrowing nations to accept loans beyond their ability to pay.

Without a country loan limit, the nine largest American banks lent $30.5 billion to just three countries--Mexico, Brazil and Argentina--or an amount well over the banks' total capital of $27 billion. A one-year moratorium on interest and principal repayment by these three countries would cause losses to these banks of one-third of their capital.

Even if that did not trigger an insolvency for one of the banks, Cline points out, all of the banks would have to reduce their total loans by about $150 billion to maintain the capital-loan ratio mandated by law. That would trigger a massive deflation for American business.

Second, there is a growing awareness that much of the total outstanding debt of 500 to 600 billion dollars will never be paid off, no matter how much money the IMF and the banks pump in during the present emergency efforts to avert disaster.

New York Banker Felix Rohatyn and Princeton economist Peter B. Kenen, among others, have suggested that perhaps half of the outstanding commercial short-term debt, written at 1981's and 1982's gouge-'em interest rates, be converted into longer-term loans at 6 percent.

That means that the banks would have to eat some losses on their loans in exchange for a better chance of getting more back later. Sen. Bill Bradley (D-N.J.) has suggested a number of ways of consolidating these debts in a manner similar to the way the U.S. government stabilizes the housing market by buying up mortgages at a discount.

The potential problems are so grim that neither Congress, nor foreign legislators, nor the international bankers likes to face them. But everybody better start the process, for time is running out.