The Organization of American States voted yesterday to convoke a foreign ministers' meeting here Thursday to consider ways of helping end the bloody civil war in Nicaragua.

They will explore whether the OAS, either collectively or through the efforts of individual members, can play a mediator's role in the conflict between Nicaraguan President Anastasio Somoza and the various forces arrayed against him in that tiny Central American country.

Although the so-called "meeting of consultation" technically will be at the foreign ministers' level, it was not immediately clear how many of the Western Hemisphere's foreign ministers actually will attend. Under AS [WORD ILLEGIBLE] actually will attend. Under OAS ambassadors to represent, and a majority are expected to do that.

State Department sources said that, although a final decision hasn't been made, the United States probably will be represented by OAS Ambassador Gale W. McGee rather than Secretary of State Cyrus R. Vance. However, diplomatic sources said that some Latin American foreign ministers, particularly those from Central America, are likely to attend.

The meeting, which was proposed by Venezulela, has strong backing from the United States, which has been calling in repeatedly stronger terms for Somoza and his foes to accept a "mediated solution" to their escalating violence.

U.S. officials are known to believe that the best hope of a solution would be offered by a Somoza agreement to step aside. However, because of President Carter's pledges not to intervene in other country's internal affairs, the United States so far has refrained from any steps aimed at directly forcing Somoza out of the presidency.

Instead, Washington has been pushing the less direct approach of mediation, although the practical effect of such a step would, almost by definition, mean an end to the 45 years of dictatorial rule that Somoza's family has exercised over Nicaragua.

Somoza'd domestic opposition currently ranges from leftist guerrilla forces to important elements of the Nicaraguan business community and the Catholic Church. Any mediated solution acceptable to these diverse groups would require at least a considerable relaxation of Somoza's iron grip on Nicaragua and probably his resignation as will.

In addition to backing the OAS meeting, U.S. sources said yesterday, Washington is also pressing its mediation effort through private contacts with the Somoza government and such other interested states as Costa Rica and Venezuela.

As part of that effort, the State Department announced yesterday William E. Jorden, U.S. ambassador to Panama, began a tour of eight Latin nations Sunday in an attempt to encourage a "multilateral mediation effort in Nicaragua.

"This reflects the U.S. conviction that prompt mediation is essential if further bloodshed and tragedy is to be avoided," the department said.

Jorden is going to Panama, Costa Rica, Guatemala, El Salvador, Honduras, Colombia, Venezuela and Mexico.

The Nicaraguan conflict has spilled over into a nasty dispute with neighboring Costa Rica over charges of border violations. Costa Rica claims Nicaragua has invaded its terrority and attacked unarmed civilians, and Nicaragua contends Costa Rica has been giving refuge to anti-Somoza guerrillas.

At yesterday's OAS meeting, 23 members voted to convene the foreign ministers' meeting, with Paraguay voting against and Trinidad abstaining. Nicaragua's ambassador, Guillermo Sevilla-Sacasa, said his government wants the meeting so it can "demonstrate to the world how foreign interventionists are trying to implant Marxist-Leninist ideals" in his country.