Again the Reagan administration gears up to ask for military aid to the insurgents in Nicaragua. But before that familiar debate drowns out all else, people ought to look at some diplomatic prospects stirring faintly -- very faintly -- at the same time.

First there is the new oxygen, as a Latin diplomat puts it, flowing to the Contadora peace-seeking campaign. The four original partners (Mexico, Venezuela, Colombia and Panama) are suffering from assorted political aches and pains, but four more recent democratic recruits are coming on strong: Argentina, Brazil, Uruguay and Peru. At Caraballeda, Venezuela, last Sunday, all eight of them took a fresh vow to persevere.

Then there is the election of Vinicio Cerezo in the key Central American country of Guatemala. His inauguration on Tuesday was attended by the presidents of both El Salvador and Nicaragua, who, according to a news report, "talked animatedly." Cerezo intends to organize a Central American summit to advance a Latin peace initiative. As someone determined to keep Guatemala on a course friendly to Washington but apart from its hard-driving policy toward Nicaragua, he induced all his Central American guests to sign on the Caraballeda statement.

Here in Washington there is a tendency to salute Latin America's would- be peacemakers and temperature- lowerers publicly but to dismiss them privately as irrelevant and ineffective, not to say sometimes hypocritical. As vexing and inconsistent as our best Latin friends can be, however, we should be alert to what drives so many of them to reach out for regional negotiations, even while the United States grits its teeth and says that the only choices are battle and surrender.

The Latins do not want to see Centrl America further torn by war. They do not want the hemisphere opened wider either to communist penetration or to American intervention. They fear their own fragile societies will be infected by the Central American disease of violence and polarization and distracted from their proper agenda of coping with the immense demands of modernization.

So it is not merely a weakness for posturing and platitudes that explains why Latin America's hard-pressed Alfonsins and Cerezos are willing to invest their scarce international assets in the risky business of a Central American settlement.

But what kind of a settlement? Is it one that could command at least a rough consensus over time, as it must to work? Is it reasonably simple and gimmick-free?

We have to go back to Contadora, the ostensibly dispensable Contadora, the Contadora that can easily become a disguise for handwringing, and get a fresh grip on the essence of it.

The essence of it is that it is made by Latins for Latins -- for all kinds of Latins, including the Sandinistas. It is a broad and necessarily fuzzy statement of the Latin political culture, whose salient elements are a sense of common Latin-ness, a respect for national differences (nonintervention) and a hope for an eventual shared future (democracy and development).

Think of it, too, as a rather patient and forgiving culture: it does not ask everyone to reach all the same targeted goals at once. It's enough that they're heading the right way. Precisely in this tolerance of delay and national variation lies the softness, but also the promise, of Contadora.

Here we must try to pin down just why Contadora has lagged so far. It's not that its arrangements for regional security are inadequate, although they are proving awfully hard to put in place. It's that Nicaragua has resisted, even as the United States has pressed, the internal political shifts that are also part of Contadora: the calls for reconciliation and pluralism. The hardening American view is that peace is not possible without these internal shifts, and the evident Sandinista view is that the survival of the regime is not possible with them.

Is not the answer to work first on the urgent security questions and, meanwhile, to rely on Latin envelopment and the lowering of regional tensions to turn the Sandinistas back from their passage toward a communist police state? In some measure, the Sandinistas are already sensitive to the pleadings and standards of their hemispheric peers. In circumstances where they were not directly threatened by Nicaragua's perceived nemesis, the United States, the Sandinistas might become more sensitive to their peers.

This is the case for a security-first, pluralism-second policy. It's un but it might work. The administration's policy amounts to doing it the other way around. It's well tested, and it's not working.