For the first time in nine years, the world's trade ministers are convening today, in Geneva, as members of the 88-nation General Agreement on Tariffs and Trade (GATT) to take a close look at the international trading system.

For three days, they will debate whether to initiate a new round of multilateral trade negotiations, and whether to broaden the GATT -- which is a treaty largely limited to trade -- to cover the increasingly important areas of services (including high-technology) and investment.

But when all of the rhetoric is stripped away, the GATT ministers will be trying not to improve the world trading system, but only to put a brake on a backward slide into protectionism. The best that can be expected from this GATT meeting is limited action to slow down the steady erosion of free trade.

And even such a modest, if positive, result is not assured: the best hope of success stems from the desire of most governments concerned, that have invested much time and effort in the preliminaries, to prevent the whole enterprise from being labeled a failure.

Trade Ambassador William Brock recalled just before leaving for Geneva that after the last high-level talks -- in Tokyo in 1973 -- it took until 1979 to complete the negotiations then set in motion.

Thus, he said, no one should expect any specific deal in Geneva, or any other visible results for a long time. What Brock would settle for "is a greater establishment of political will to avoid the trap of new protectionist actions around the world, or beginning some form of trade war in which there are virtually no limits."

[In Geneva last night, Brock said that the commitment to an open U.S. market was "on the verge of collapse" because of the protectionist trade barriers imposed by other nations.]

In an opening address this morning, International Monetary Fund Managing Director Jacques de Larosiere, implored the conference not to yield to "self-interest which can only be self-defeating."

But in today's depressed world, that is a large order. In the wake of growing protectionist actions flowing out of the world-wide recession, there is a fear that there will be confrontation in Geneva, rather than cooperation, that would deepen, rather than mend, the cracks in the system.

It is a measure of the serious nature of the crisis that lately, much of the talk about the GATT meeting has not been whether it could improve the system, but whether ministers could agree to a "standstill" or freeze of additional trade restrictions.

There is a great deal of bitterness on trade issues between the United States and Europe; between Europe and Japan; and between the industrial nations as a group, and the developing nations as a group, especially those developing nations that have been gaining a bigger share of the world's industrial export markets.

The American grievance against Europe is that most countries heavily subsidize their agriculture and their aging industrial plant. France under President Francois Mitterrand has become the most protectionist nation in Europe -- the rest of the Common Market readily and bitterly acknowledges this.

The European grievance against the United States is that the Reagan administration, while touting the need for multilateral rules of law, has acted unilaterally, as in the Soviet pipeline case, and bilaterally, in establishing "voluntary" quotas on Japanese auto imports, for example.

Moreover, the United States and the Europeans still have not found a free-trade answer to Japanese superiority in manufacturing and merchandising cars, video and other equipment. And all of the rich nations together are being pressed, as they will be again in Geneva, to open their markets more fully to the increasingly sophisticated factories of the Third World.

The message hammered home by both Brock and de Larosiere is that Third World countries will never be able to pay off their huge obligations unless they have wider access to First World markets.

The agenda for the Geneva meeting is divided into three parts:

First, a renewed ministerial pledge to resist protectionism.

Second, dealing with business left over from the Tokyo round, including a "safeguards" code to minimize unilateral actions such as quotas; and a system of settling disputes.

Third, consideration of the American proposal for a "work program" for the balance of the 1980s to evolve rules on trade in high-technology items, services, and trade related investment issues.