President Anastasio Somoza touched off Intense speculation today with a trip outside the country while negotiations between the United States and the guerilla-backed junta seeking to take power here were reported at a stalemate.

There were widespread rumors early this morning that Somoza had resigned when he left Nicaragua unannounced in a private jet. By the time word had spread through the city, however, Somoza had returned from a brief trip to Guatemala, where he reportedly met with leaders of that country, El Salvador and Honduras.

Those three Central American military governments remain among the few international supporters of Somoza and reportedly have supplied the Nicaraguan National Guard with enough arms and ammunitions to continue its sputtering war against leftist Sandinista guerrillas.

While the Nicaraguan government made no official comment on Somoza's trip, U.S. Rep. John Murphy (D-N.Y.), also a strong Somoza supporter, said in Washington that Somoza was "trying to get those countries to exercise their responsibility" under a Central American mutual defense treaty.

Murphy said the meeting "was not the first in the past two weeks" among leaders of the four governments and that Somoza had asked them to help stop Sandinista activity in Costa Rica.

Officials in Guatemala, Honduras and El Salvador fear that a guerilla victory in Nicaragua will give encouragement to leftist movements in their own countries. Thus far, however, they have been reluctant to commit troops or even open support to Somoza for fear of sharing Samoza's growing hemispheric isolation.

Meanwhile, a Nicaraguan government spokesman today outlined rules for foreign press censorship announced Thursday. The spokesman said some foreign reporters were guilty of an unspecified "lack of objectivity" in their coverage of the Nicaraguan war.

He said all outgoing stories would be subject to prior approval by a three-man censorship board. Those correspondents who evaded the censorship, he said, would be judged by their published stories, and the authors of any considered "flagrant violations of objectivity" would be asked to leave the country.

The Sandinista National Liberation Front today stepped up its radio propaganda campaign, calling on National Guard soldiers to lay down their weapons and switch sides before a stepped-up offensive overthrew Somoza.

Although government officials announced major air attacks against several rebel-held cities today, the Sandinistas have called on their front-line commanders to hold current positions until further orders as negotiations continue in Costa Rica between U.S. diplomats and a provisional government junta on a political resolution to the six-week old civil war.

Spokesman for the junta the guerrillas have appointed to replaceSomoza said that three days of talks with U.S. diplomats had broken down following U.S. failure to accept a junta plan for transition of power here.

Released Wednesday, the plan called for Somoza to resign and for the junta to be installed. Following a junta-ordered cease-fire, the plan outlines a new Nicaraguan army of combined National Guard and Sandinista forces.

Initial lukewarm U.S. acceptance of the plan, the junta said, was followed by tentative State Department objections to its failure to address strong U.S. concern about adding additional moderate members to the junta and making the National Guard predominate over the Sandinistas in a future army.

While the State Department said in Washington that it knew of "no break-off in discussions," junta foreign minister Miguel D'Escoto said, "our patience with the United States has been used up."

D'Escoto said that a meeting called this morning with special U.S. Ambassador William Bowdler had been canceled because Bowdler is ill. He said, however, the junta has no particular desire to talk again unless the United States "has something important to say."

Instead, the junta is now directing its efforts at gaining international support from other Latin American governments.

While some of those governments, including Venezuela, Costa Rica and Panama, at times have joined U.S. efforts to pressure and persuade the junta to expand its membership and give more guarantees to the National Guard, D'Escoto said they have now decided to work with the junta on their own.

Thursday, junta members met in Costa Rica with former Venezuelan president Carlos Andres Perez, former Panamanian head-of-state Omar Torrijos; Costa Rican President Rodrigo Caravo and other high level Costa Rican officials. All three countries have been strong Sandinista backers.

D'Escoto said that the foreign ministers of the Andean Pact nations, including Venezuela, Ecuador, Peru, Columbia and Bolivia, to plan to meet in Caracas Sunday to discuss the Nicaraguan situation. He said the junta has requested those governments to break relations with Somoza and recognise the junta as Nicaragua's legitimate government.

These Latin American countries and others have expressed their opposition to Somoza. Thus far, however, most of them have refused to take diplomatic action against his government until they can reach agreement on joint action.

D'Escoto again denounced U.S. reluctance to pressure Somoza to leave the country until a U.S.-approved political settlement is reached. The United States has told the junta that it has Somoza's resignation "in its pockets" but will not press for it until its concerns about the new governmernt are satisfied.

"Our people are being massacred," D'Escoto said, while the United States "talks around in circles. They are trying to make us believe they can make Somoza's resignation effective in a matter of hours. We think it's criminal, and we hope for their sake their policy will change." CAPTION: Picture, Nicaraguan National Guard soldier in La Virgin looks over rifles reportedly taken from Sandinistas. UPI