IT WAS a small war -- four days, not many casulties -- but a nasty one, leaving El Salvador and Honduras without diplomatic or trade relations and shredding the Central American Common Market. The tinder had been provided by the drifting of land-hungry Salvadorean peasants across a long-disputed border and had exploded at a football game: hence the misleading label, the "soccer war." That was in 1969.

From that point, however, things slowly got better. The Organization of American States, which had soon smothered the shooting in diplomatic batting, provided a continuing observer presence through the year and eventually arranged mediation. The mediator, Peruvian jurist Jose Lusi Bustamante y Rivero, helped bring in a peace treaty last month. Signed in Lima, it will be formally deposited at the OAS this evening. The treaty provides for, among other things, a procedure by which to settle remaining border differences, the restoration of trade and diplomatic ties and a commitment to renew the regional common market.

While Honduras was responsibly cooperative, El Salvador took the lead in pushing treaty negotiations to a conclusion this fall. The civilian-military junta struggling to hold on in civil-war circumstances in San Salvador evidently wanted a diplomatic success to boost its prestige. Terrific. What more legitimate way is there fo a government to earn public standing than by contributing effectively to the peaceful settlement of internationl disputes"

The junta's political rivals are furious, saying, for instance -- without evident justification -- that the treaty was arranged merely to make it easier for the junta to deprive anti-government guerrillas of Honduran sanctuary. But the achievement of El Salvvador and Honduras needs to be celebrated, not knocked down. There are not so many positive things going on in Central America that any one of them can be denigrated without good cause.