WITH THE AGREEMENT between Brazil and Argentina not to pursue nuclear weapons, life in the Western Hemisphere becomes a little safer. Previously both countries were in the position of saying that they would not build nuclear bombs, while neither fully trusted the other. Now each has promised to open its nuclear facilities -- all of them -- to inspection by the other.

That's next best to their actually signing the Nonproliferation Treaty and allowing the International Atomic Energy Agency to inspect all of their nuclear operations. Both Argentina and Brazil unfortunately still balk at that. But if these two Latin countries now allow each others' inspectors into their plants and laboratories, including previously secret ones, that's a major contribution to stability in South America.

Six countries have undisclosed nuclear weapons or, in recent years, have been working toward them. They fall into two categories. Israel and South Africa are countries that see themselves surrounded by hostile neighbors that greatly outnumber them. The other four are pairs of regional adversaries. India has exploded what it archly calls a "device," and if Pakistan doesn't yet have one too, it is very close.

The rivalry between Argentina and Brazil has always been quite different from that in South Asia, with none of the entrenched ethnic and religious passions that make the arms race there particularly dangerous. A lot of the tension between the two Latin countries was artificially pumped up by the military governments that used to run them -- a tactic by the generals and admirals to justify their own aggrandizement and their inflated budgets. When civilians took power in the mid-1980s, the two countries immediately began giving attention to their menacing (and extremely expensive) nuclear weapons laboratories.

The Argentines, under the determined leadership of Raoul Alfonsin, put an end to their nuclear weapons program. But in Brazil, Jose Sarney was a weak president constantly bidding for support from the generals, and a secret effort to build weapons proceeded parallel to the open development of nuclear power for civilian purposes. It has only been within the past year, with Mr. Sarney's replacement by President Fernando Collor de Mello, that the secret bomb effort has been exposed and terminated.

That recent experience demonstrates once again that, as in all things nuclear, reliable verification and inspection are the key to any solid agreement. But it also demonstrates that, even among countries that once seemed unpromising candidates, regional nuclear arms agreements are possible.