Four Latin American countries attempting a peace initiative in Central America independent of United States participation have agreed to send a small group of observers to the troubled border between Costa Rica and Nicaragua, the group announced in a bulletin issued here this morning.

The latest move by Mexico, Venezuela, Colombia, and Panama to "make a study" of the border situation falls far short of the "peace-keeping force" Costa Rica requested from the Organization of American States last week. But according to senior Latin American officials informed about the negotiations, the so-called "Contadora Group" had difficulty reaching even this stop-gap consensus in its efforts to find an overall framework for a negotiated end to the area's widening conflict.

The revolutionary leftist Sandinista government in Nicaragua, accused by Washington of aiding leftist guerrillas in El Salvador, is itself under steady attack by U.S.-backed rebels who operate with the cooperation of its northern neighbor Honduras. Now a second group in southern Nicaragua under exiled ex-Sandinista commander Eden Pastora is working to open a new front operating along Costa Rica's vulnerable border.

The Costa Ricans say that because they have no regular army they are powerless to stop the operation of the anti-Sandinista rebels and are unprotected from any retaliation Nicaragua might take as the result of those activities.

The Costa Ricans asked the OAS specifically for a force capable of exercising effective vigilance in the Costa Rican zone bordering Nicaragua. This was widely taken to mean a military force, but in the days since the request was made the Costa Ricans have broadened their definition of what they want.

In an interview Wednesday, Costa Rican President Luis Alberto Monge said his country wants "to be recognized as neutral by the rest of the world" and that the purpose of the "peace mission" requested from the OAS would be "to guard our neutrality and to certify to the world that we are not involved and not condoning actions against Nicaragua."

Although by aiming their request at the Contadora Group the Costa Ricans hoped to avoid such criticism, both the Mexican and the Panamanians expressed concern that any international "peace-keeping" force would be the precursor of major direct U.S. military intervention in the region. Mexico immediately rejected the idea last week. The Panamanians said they might consider some civilian presence, while according to senior officials involved in the four countries' discussions, the Venezualans and Colombians were willing to entertain the idea of sending troops to the area in such a capacity.

The communique this morning, issued as a "informational bulletin," came after the foreign ministers stayed up for the second late night in a row trying to thrash out their differences.

The "observation commission" they finally agreed to send to the border, if both Costa Rica and Nicaragua acquiesce, as expected, would be made up of two representatives from each of the four Contadora countries plus such advisers as the commissioners may consider necessary. They may also consult with "international experts," the bulletin said.

This morning's communique revealed few other points of agreement beyond the statement of general principle about self-determination and nonintervention in the affairs of other countries, which it would be "highly desirable" for international organizations to support and strengthen.