THERE IS A STRAIN of trouble spreading in Latin America that is potentially at least as serious as the fighting in Central America, although it has received little public or diplomatic attention. It is an accelerating interest on the part of several countries in acquiring nuclear weapons technologies and perhaps the weapons themselves.

Argentina is the leading nuclear power in Latin America. It has refused to sign either the worldwide Nuclear Non-Proliferation Treaty or the regional Treaty of Tlateloco, which would establish a nuclear-weapons-free zone in the area. The Argentine government has hinted for some time that it has the ability to build atomic weapons and has refused to renounce so-called "peaceful" nuclear explosions. Last week, the director of Argentina's atomic energy program, Adm. Castro Madero, went further than official spokesmen have in the past, saying his country might want to use nuclear explosions for such enterprises as mining and canal construction. Adm. Madero's statement could be laying the groundwork for an Argentine nuclear test.

Rumors have been circulating for some time of complaints raised at the International Atomic Energy Agency about Argentine activities, including an illegal diversion of fuel from its safeguarded reactor. Argentina is also building an unsafeguarded heavy water reactor capable of producing large quantities of plutonium, the optimal weapons fuel. Administration spokesmen now put Argentina near the top of the list of potential new nuclear powers.

Speaking of the optimal weapons fuel, across the border, Brazil has built an unsafeguarded pilot reprocessing plant and is working on a breeder reactor. These projects, which rely on German and Italian aid, will make Brazil self-sufficient in plutonium. In addition, projects that are Brazilian-built and -run are also under way, and the intention seems to be to achieve self-sufficiency in every stage of the nuclear fuel cycle. At an air force facility, construction of centrifuges for uranium enrichment (the method being used covertly by Pakistan) is reported to be taking place in a bomb-proof building. The country's fourth major nuclear center is under construction by the army. All of this is happening at once, despite severe strains on the Brazilian economy and a crushing foreign debt.

Both Brazil and Argentina are also becoming nuclear suppliers to other nations in their own right. Within their capabilities, each appears eager to supply whatever its customers want. Brazil has an extensive agreement with Iraq that may have included the secret supply of nuclear fuel for irradiation in Iraq's now destroyed research reactor. It expects the Iraqi agreement to be first of several with Middle Eastern countries. Argentina has signed nuclear cooperation pacts with several Latin nations and has built a research reactor in Peru.

In fact, there may no longer be much need for non-nuclear weapons states even to worry about the major suppliers' reluctance to export weapons-related technologies and materials to them. If the German and Italian programs in Brazil are not sufficient evidence of a renewed willingness to exchange longterm security for immediate commerical advantage, there is the bidding war under way in Mexico. Those who now are competing to become the supplier to Mexico's ambitious nuclear reactor program have been asked to provide the Mexicans with access to advanced technologies including enrichment and reprocessing.

The American bid includes extensive manpower training, an as yet undefined promise of "follow-on cooperation" in advanced weapons-related technologies, and a stated interest in Mexico's "becoming a close partner," presumably with rights to the extracted plutonium, in the administration's hoped-for American reprocessing plant. There is not a word about this country's non-proliferation goals or a hint that any technology may be considered by the government to be inappropriate for export. To public knowledge, the United States has made no effort to reach agreement among the suppliers not to undercut each other by offering weapons-related technologies. It seems likely that by the time Mexico reaches its decision later this year, the informal suppliers' agreement not to export such technologies reached a few years ago will have been abandoned without any serious effort having been made to rescue it.

The attempt to inhibit the spread of nuclear weapons is not an all-or-nothing proposition. It is a continuing drive to restrict the number of nuclear- armed nations, to minimize the amount of plutonium in international commerce and to build political incentives not to acquire nuclear weapons. It is (or was) an effort to slow an obviously dangerous international trend. But there is more than a little evidence that, without American objection and perhaps even with tacit American encouragement, the impediments to the spread of nuclear weapons to ever more countries are being dismantled -- or just shoved aside.