Businessman Alfonso Robelo resigned from Nicaragua's revolutionary junta today charging that the Sandinista Liberation Front had violated the pledges of democracy it had made to other political groups before it came to power.

The resignation of Robelo came three days after Violeta Chamorro left the junta citing poor health and leaves the government in the hands of the leftist Sandinista Front.

The other three members of the junta -- Sergio Ramirez, Moises Hassan and Daniel Ortega -- are members of the Sandinista Front that overthrew dictator Anastasio Somoza last July. Chamorro and Robelo had been considered the representatives of the business community on the junta, which rules in conjunction with the nine-member Sandinista National Directorate.

The resignations of Robelo and Chamorro have produced the most serious political crisis the nine-month-old revolutionary government has faced. It comes at a time of economic problems and growing discontent among the middle class and business people.

Adding to the tensions was a strike that closed La Prensa, the country's only independent newspaper. The strike grew out of a dispute within the Chamorro family, which owns La Prensa, over whether the paper follows the government line too closely.

A spokesman for Robelo's Nicaraguan Democratic Movement said as many as 54 other members of the party may also leave the government. But junta member Ramirez said fewer than a dozen had resigned.

Ramirez and Hassan made a formal appearance before the cabinet and journalists tonight to announce that the resignation had not caused a crisis and that "the immense majority of the Nicaraguan people" back the government.

Nevertheless, two other officials connected to the business community reportedly resigned in the past week -- Arturo Cruz, head of the Central Bank, and Luis Carrion Montoya, head of the national banking system.

Robelo told reporters that his party had decided to withdraw from the coalition because of a decision by the junta to enlarge the Council of State, a legislative body to be made up of representatives of the political and economic groups chosen before the junta took power. The Council of State is to hold its first session May 4.

The junta yesterday enlarged the Council of State from 33 to 47 members, adding representatives of the Army and several large local organizations formed by the Sandinista Front.

In announcing the new composition of the Council of State, junta member Ramirez said the fact that the Sandinista Front has a majority "reflects the concrete and objective reality of the balance of political forces in Nicaragua."

Ramirez said the Council of State would be "an experiment" in "democratic institutionalization" and would remain in power until there are "elections or some other form of transition" to a more permanent form of government.

All business groups and several political parties not allied with the Sandinista Front have insisted that the Council of State have the membership outlined in the Fundamental Law

Ramirez and others said that would be impractical since some of the organizations that worked with the Sandinistas to overthrow Somoza no longer exist while important new organizations have come into being. Robelo proposed a 33-member council of State including representatives of all the new organizations, but the other junta members insisted on their original proposal, which favors Sandinista groups.

Robelo said he still supports the revolution, and will work to "forge a democratic, free and revolutionary Nicaragua."

In their statement tonight Ramirez and Hassan also said the government will continue to follow its policy of a mixed economy and "pluralist participation."

"National unity," they said, "is necessary now more than ever to continue the climate of stability . . . and public liberty that has earned the Nicaraguan revolution "the respect of Latin American and the world."

Ramirez said no decision has yet been made on whether to replace the two junta members who resigned. He said it is possible that two new members will be named "who represent different sectors of the country."

There was no immediate reaction from the Sandinista Front to Robelo's resignation. But the Front's attitude was reflected in comments by Danilo Aguirre, a top editor of La Prensa, who is a Sandinista.

"What is happening at La Prensa is not an isolated situation," Aguirre said. "It is part of a vast plan by the most reactionary groups, and Robelo has entered into that game of destabilizing maneuvers. . . .

"The working class is in power here through the Sandinista Front and what they [the business community] are doing is . . . rejecting an opportunity to coexist within the revolutionary process."

People who are unhappy with the Sandinista government have complained of restrictions of freedom of expression, the failure to set a date for elections and growing ties with communist countries.

The Sandinistas insist that the new Nicaraguan government conducts an independent foreign policy. They say they must solve the country's various economic problems before holding elections and that there is far more political freedom here now than there was under Somoza.