Have you ever heard of the Paris Club? Chances are you haven't, unless you're a high-ranking official of one of the 16 rich industrial countries that makes government-to-government loans, or a worried representative of a borrowing nation knee-deep in debt.

But as the world's worst post-war recession continues with no visible relief, the Paris Club (which meets at the Kleber Centre in the French capital) will be increasingly in the news as it attempts to rewrite loans that otherwise would be in default. This process, known by the fancy term "rescheduling," is an effort to apply easier terms to big chunks of a $500 billion Third World debt, so as to keep both lenders and borrowers afloat.

Meanwhile, the "London Club," private sector counterpart of the Paris Club, gets together on an ad hoc basis in many different cities when it becomes necessary to stretch out the loans made by banks -- big ones and smaller ones -- to the developing nations.

How to keep the financial system lubricated at a time of declining world trade was the central theme of a two-day private bankers' conference put together by the Global Interdependence Center last week in Philadelphia. Just back from the latest Paris Club huddle, U.S. Ambassador Charles Meissner, special State Department negotiator for economic matters, pointed out that prior to 1977 there might have been one or two reschedulings a year, usually triggered as much by civil disturbances as by economic mismanagement.

But under the cumulated impact of two oil shocks, and the problem compounded by over-lending and over-borrowing, a rescheduling is no longer a unique event. Meissner says that 15 reschedulings are under way under the aegis of the Paris Club, and perhaps another 10 countries are in enough trouble to be making reservations for a Kleber Centre hearing soon.

Horst Schulmann, who was deputy finance minister under West German Chancellor Helmut Schmidt, puts the current and prospective number somewhat higher -- around 40 -- and adds that "the number of firms in the banks' intensive care units is also rising rapidly." He wryly noted in Philadelphia that "the 1980s may well be remembered as the decade of the reschedulings."

Meissner says that "as I see it, what we are dealing with is a transition from a period of inflation and negative interest rates in the past 15 years to a period of deflation and positive interest rates." When interest rates are negative, it makes sense to borrow as much as incautious lenders will shell out. But now, some of the borrowing countries find that 50 percent or more of their earnings from export go to pay interest alone.

But here is where the problem becomes exceedingly complicated: it does little good to work out an easier payment schedule for Mexico, Poland, Argentina, or dozens of other countries that borrowed too much money if they can't sell enough of their products to the Western World to meet even the relaxed terms.

Jan Tumlir, research director of the General Agreement for Tariffs and Trade (GATT), put it best: If trade restrictions grow, no amount of reschedulings can make the repayment of principal and interest low enough for the poorer nations to manage.

Moreover, if commercial banks -- in atoning for their extravagant sins of the last decade, when they were literally pushing money on unsophisticated Third World borrowers -- now cut and run, they will be assuring a massive default, especially in Latin America and Eastern Europe, where the problem is the worst.

In turn, this crisis in the Third World would dramatically reduce the industrial nations' exports to the borrowing countries. It's not generally realized, for example, that in 1981 the United States' best customer was the group of non-OPEC developing countries, which took 32 percent of our exports, much more than the Common Market (22 percent) or Canada (17 percent).

Former Treasury official C. Fred Bergsten estimates that two-thirds of the current U.S. recession can be chalked up to declining exports, which in turn can be traced to an over-valued dollar, which in turn can be traced to Reaganomics' contentration on excessively tight money policy.

As all of these problems merge into one massive headache, the world's trade ministers are getting ready for the first top-level GATT meeting in nine years at the end of this month, in Geneva, to try to put a halt to growing protectionism. They must deal with the fact that for the first time in years, the volume of world trade has begun to shrink -- and each nation is trying to maintain or increase its share of a static pie.

Increasingly, as Tumlir said, the big nations that talk free trade -- the United States and Common Market countries among them -- have been signing bilateral deals as nationalist fervor abounds. It's easy enough to see why: Assistant U.S. Trade Representative Geza Feketekuty makes the point that between 1979 and 1982, auto industry employment here fell 34 percent, while imports rose 43 percent. In steel, employment dropped 48 percent while imports rose 46 percent.

Feketekuty doesn't present these figures to rationalize protectionism, as former vice president Walter Mondale seems to be doing, but to explain why it's necessary "to find some way of reaching an understanding with each other as to how we're going to limit the overall reaction to this sort of thing." So far, both Europe and the United States have reacted to this kind of problem by imposing quotas.

"When you have this kind of [worldwide economic slump]," Feketekuty said, "obviously you're going to get a very considerable pressure to solve problems by reducing the pressure from imports. Secondly, regardless of whether you think the other fellow was cheating or not, you say, 'My situation is tough and difficult and you've got to do something about it.'

" . . . at a time like this, people become far more sensitive about what they view as cheating by others. When things are going well, people say, 'I don't really like how the other fellow does his business but I'm doing all right.' Now their notions of what's fair become far more sensitive.

"Finally, at a time like this, obviously governments are pressed into doing many other things which, at least from the point of view of other countries, tend to take on a character of beggar-thy-neighbor policies. And this is always the danger. Because once you go down the treadmill of beggar-thy-neighbor policies the other country feels that it is totally justified in following suit."

Nearly half of all world trade, according to Tumlir, is already limited by non-tariff restrictions and barriers. There is a host of subsidies, tax-concessions, and other subtle and not-so-subtle ways that countries have of keeping imports from others down, and giving your own exports a shove. By and large, the U.S. market is more open than others, but the Reagan administration has eroded its free trade rhetoric with protectionist moves in auto, steel, sugar, and other areas.

Bergsten, in a keynote address to the Global Interdependence Center's conference, called for "a standstill agreement" at Geneva that would require all countries to avoid any new trade barriers for the duration of the agreement.

He said he and his colleague, William R. Cline, would shortly publish a detailed set of recommendations for a new trade policy that would include conversion of all remaining non-tariff barriers to tariffs, and then phase them out over time.

Bergsten put forward what he called "the bicycle theory" of trade, according to which the system either becomes more liberal or lapses into protectionism. He also warned that the GATT ministerial meeting would face failure unless a conscious link is made between international monetary and trade arrangements, especially to curb excessive fluctuations among national currencies.

But with the GATT meeting only two weeks away, there is nothing on the agenda to deal with international monetary arrangements, or any kind of joint effort between GATT and the International Monetary Fund.

As the knowledgeable Schulmann said here, "cooperation between the United States, Common Market, and Japan will make or break the international system." But given the recent track record, he is gloomy: "the situation may very well be that the reality of interdependence has outpaced our intellectual power to analyze the problem and to build appropriate models" to solve it.

Is this too pessimistic? Chandra Hardy of the World Bank thinks so. She believes that even if the First World has condemned itself to slow growth for the rest of the century, there is a source of dynamism in the Third World, which can continue to outperform the industrial bloc -- provided bankers, the IMF, and the World Bank don't cut off capital flows.

"The world is not so much in crisis as in transition," she says, "and the problem is that the transition isn't being well managed."

There are no easy answers to an exceedingly complicated problem. The leadership that would enable Trade Ambassador William Brock, the EEC's Sir Roy Denman and their counterparts to achieve a breakthrough in Geneva must come from the very top.