The most popular hero of the Nicaraguan revolution resigned from the Sandinista government in Managua and left Nicaragua last night for Panama, causing consternation among many Nicaraguans and raising speculation that strains within the Sandinista leadership are starting to show.

Eden Pastora, 43, became internationally famous as "Commandante Zero" while leading the takeover of the Nicaraguan National Palace in 1978 that marked a beginning of the end for the Somoza dictatorship. Pastora said in his officially released letter of resignation as vice minister of defense that he was leaving to fight in other revolutions.

"I am going to the trenches where the duty of an internationalist combatant conducts me," he wrote armed forces commander Humberto Ortega.

The statement did not specify where Pastora intended to fight, but Guatamala and El Salvador were clearly implied. "I cannot tolerate seeing peasants burned alive in embassies, nor can I tolerate seeing priests shot while they conduct masses or in the conduct of their Christian duties. I cannot tolerate seeing the killing by hunger of defenseless people in brother nations while I cannot fire my revolutionary rifle," the letter said.

The Sandinista National Directorate issued a statement last night saying it would not accept Pastora's resignation or that of the vice minister of the interior, Jose Valdivia, who accompanied him. But Nicaraguan immigration officials said both men, accompanied by about 10 other people whose names were not immediately available, left the country last night.

Surprise and sorrow marked the reaction of many Nicaraguans. "We all feel it very much," said one young woman who works in the government. "It was so unexpected now, just 10 days before the second anniversary of the revolution."

The letter suggested what many Nicaraguans have suspected, that Pastora was not ahppy with his role as an administrator, even though he was in charge of building up the militias into a force of more than $100,000.

"He was always more of a guerrilla than a desk person," said a diplomat.

Despite his outspoken defense of the Sandinista regime, he was never considered as ideologically oriented as many of the leftist commanders.

Although clearly the most popular Sandinista leader -- often provoking spontaneous and prolonged applause whenever he appeared in public -- Pastora was never given the rank of commander of the revolution or included in the all-powerful Sandinista National Directorate.