SUNDAY WAS INDEED a happy Easter for Argentinians, whose president, Raul Alfonsin, convinced rebel army officers to abort a plan to launch an offensive against the nations's still fragile democracy. For four days, the officers had plotted in a military compound outside the capital. Alfonsin proved that even in blood-soaked Latin America, the power of suasion can exceed the power of arms. The peaceful victory offers others in a war-torn world an eloquent lesson.

Alfonsin credited the political opposition, labor organizations and business leaders for his victory over the mutinous officers. He was right to do so. In Argentina, contentious factions still contend, but they also band together to oppose any who would replace the uncertain stability of democracy with the certain trauma that would follow its over-throw.

Alfonsin recognized that permitting loyal opposition would safeguard his government more effectively than repression. It is a lesson too often lost on Alfonsin's counterparts in other Third World nations, such as Chilean President Pinochet. The United States, for its part, should realize that support for rightist strongmen who do not tolerate peaceful opposition seldom invites accomplishments as stirring as that of the Argentinian president.

Fortunately, in the case of Argentina at least, the United States has begun to overcome its past record. Just a few years ago, when a military junta controlled Argentina and carried out the bloody "dirty war" against Argentinian civilians, the United States government vigorously backed the junta. Sunday, however, it was these very military officers whose rebellion was so successfully quelled.

Alfonsin's victory, however, will not quiet the unrest that surges through his armed forces. Argentinian democracy is safer this week than last, yet still not safe. Nonetheless, Alfonsin's achievement may be a hopeful sign for Latin America's attempts to nurture democracy.