The United States and several Latin American countries are on the verge of arranging the first hemispheric endorsement of the scheduled elections in El Salvador, diplomatic sources said tonight.

The potential endorsement by the General Assembly of the Organization of American States, which is currently meeting in this sunny Caribbean island, was a priority subject in private meetings today between Secretary of State Alexander M. Haig Jr. and several hemispheric foreign ministers, the sources said.

Such an expression by the OAS would bestow greater regional and international prestige to the elections called for next March by the embattled civilian-military junta led by Salvadoran President Jose Napoleon Duarte.

International recognition of the planned elections is considered important to efforts to consolidate the U.S.-backed Duarte government and to head off demands that political recognition and a negotiated share of power be granted to the Salvadoran guerrilla movement and its political arm, the Democratic Revolutionary Front (FDR).

Haig had been scheduled to address the OAS meeting in the morning session today, but did not because the slow-moving session fell behind its agenda. The speech may be rescheduled for Friday, aides said.

The March elections in El Salvador, which the opposition movement has so far rejected, are Washington's answer to calls for a negotiated solution, such as those expressed by a senior Salvadoran guerrilla commander in an interview published today by The Washington Post.

Informed of the Salvadoran commander's offer to negotiate without prior conditions, Haig said today, "If he's talking about negotiating a share of power, that's nothing new."

"If he's talking about putting down his AK47 a Soviet-designed weapon and taking his chances in a democratic election, that would be different," Haig declared, saying that would clearly be a breakthrough.

Salvadoran Foreign Minister Fidel Chavez Mena reiterated here tonight that the political arm of the opposition forces has an open invitation to join an interparty dialogue to negotiate the conditions for the elections. Chavez Mena carefully qualified the offer to include negotiations limited to the context of the planned balloting.

An OAS endorsement of the electoral process in El Salvador is seen as a way to head off a resolution sponsored in the United Nations by France and Mexico calling for broader negotiations than favored by the United States. A Latin American diplomat who conferred with Haig today said the secretary of state showed great concern in private that the French-Mexican resolution might pass, adding, in Haig's view, a new complication to the Salvadoran struggle.

Another diplomat who conferred with Haig, Argentine Foreign Minister Oscar Camilion, said they discussed the proposal for endorsement of the Salvadoran political process. Camilion said he advised Haig "to get wide support" in the OAS for the endorsement to give it maximum impact.

"The problem is not to get a majority in the OAS for the resolution, but to get a political majority with very wide support," Camilion said.

The proposed endorsement, which reportedly will be sponsored by Venezuela and Colombia, would have two elements, Camilion said, support for the political process in El Salvador and repudiation of all forms of intervention and threats in the Salvadoran situation.

The ticklish part for the resolution's backers is to find wording that will draw the greatest support, he said.

Another idea being broached privately to deal with the volatile Central American situation is to invoke the 1947 Rio Pact permitting hemispheric nations to order sanctions, including armed action, in the face of threats to territorial integrity, sovereignty or political independence of a hemispheric signatory nation.

El Salvador and Guatemala, which are facing insurgencies allegedly aided by outside forces, are signatories to the pact.

A Salvadoran official, who asked not to be named, said his government is not considering seeking the use of the Rio treaty now.

U.S. officials also have been privately discussing the Rio treaty as a way to give legitimacy to a potential blockade against Nicaragua or other military actions in the hemisphere