Nicaragua's provisional junta said today that several Latin American countries have expressed initial approval of its peace program outlining a transition of power here, but that the United States had not yet commended on it.

The plan, released by the junta last night in Costa Rica, calls for the immediate resignation of President Anastasio Somoza, the installation of the guerrilla-backed junta and a cease-fire between the Nicaraguan National Guard and the Sandinista National Liberation Front.

It proposes a new armed force composed of both the Sandinistas and National Guard, and guarantees safe passage out of the country for all Somoza government officials and military personnel "not found involved in crimes against the people."

The plan offered the most assurances to date for the National Guard, whose future has been a strong concern of both Somoza and the United States.

But while initial reports from Costa Rica indicated the proposal was a compromise reached in discussions with U.S. Ambassador William Bowdler, the junta today said it was a junta initiative and that Bowdler did not appear pleased with the program.Bowdler is an experienced diplomat who handled an aborted Nicaragua mediation attempt last fall and has been negotiating U.S. concerns with the junta this week.

The plan was distributed yesterday afternoon in Costa Rica to Bowdler and representatives of the Andean Pact Nations, including Venezuela, Ecuador, Peru, Colombia and Bolivia. While the Latin nations responded favorably within hours, the junta said, Bowdler said he would have to refer the document to Washington for consideration.

U.S. officials were known to be dissatisfied that the documents, the first the junta has released concerning the transfer to power, made no reference to State Department concern over the composition of the five-member junta itself.

In exchange for facilitating Somoza's resignation and a cease-fire, the United States has asked for junta expansion with more political moderates and, prompted by fears of future Sandinista radicalism, asks guarantees for the continuation of the National Guard as Nicaragua's main armed force. The junta has strongly resisted, maintaining that further dilution of its membership or special concessions to the much hated guard would "betray the liberation struggle" and cause it to lose popular support.

The State Department has expressed concern that junta agreements may not be binding on the Sandinistas, despite the fact that the guerrillas selected and appointed the junta and have pledged their allegiance to it.

Moises Hasan, leader of the guerrilla-allied United People's Movement and considered the junta's most radical member, has not attended any of the Costa Rican negotiating sessions. Hasan reportedly was wounded in a guerrilla retreat from Managua last month.

Daniel Ortega, the only junta member who is also a member of the Sandinista National Directorate, came to San Jose to talk with Bowdler over the past few days and participated in drawing up the transition plan.

Sources said the plan was read last night to all Sandinista front line commanders over a ham radio frequency used by the guerrillas. They said Ortega immediately left Costa Rica for a tour of rebel-held areas in Nicaragua to further explain the program.

The Sandinistas now control several major Nicaraguan cities, including Leon, Masaya, Matagalpa, the smaller cities of Diriamba and Jinotepe and about 15 other towns as well as scattered rural areas in the country.

There have been repeated reports of infighting and power struggles between two Sandinista factions, the moderate Insurrectionalists and radical Prolonged Popular War groups in Leon, the longest rebel occupied city.

Guerrilla spokesmen yesterday acknowledged the difficulties and said problems had arisen because those in charge of organizing the municipality are military rather than political commanders. They said several high-ranking Sandinista leaders had been dispatched to the city to attempt to sort out the problems.

Sandinista spokesmen also again denounced reported executions of Somoza supporters in some rebel held areas. They maintained that "summary justice" was not the policy of the guerrilla organization, but said that some undisciplined individuals may have broken orders because of rising tension as the civil war continues. CAPTION: Picture, Sandinista rebels hold their weapons overhead to cheer their complete takeover of the town of Jinotepe. UPI