Against a background of increasingly radical political rhetoric here in recent weeks, Sandinista leader Daniel Ortega is visiting Moscow this week, apparently to seek aid that could bring Nicaragua closer to an open proclamation of a Marxist-Leninist state.

Ortega, who is coordinator of the government junta and one of nine top Sandinista commanders, was guest of honor at a dinner in Moscow hosted by Soviet leader Leonid Brezhnev tonight.

Many Nicaraguans believe the mission will be decisive for the country's immediate future, depending on whether the Soviets decide to provide desperately needed funds to the government here and, in effect, subsidize the road to socialism as was the case with Cuba.

Until recently Nicaragua's revolutionary leaders had down-pedaled the Marxist aspects of their ideology, saying they represented a uniquely Nicaraguan, Sandinista philosophy.

Growing domestic and international pressures, many promoted by Washington, have put the Sandinistas in an increasingly defensive posture.

As the consensus appears to have grown among the leadership that there is no hope of reaching an accommodation with the United States, Sandinista ideology becomes less a vague amalgam of nationalism and social democracy and tends more overtly toward communism and toward alignment with the Soviet Bloc.

At the same time, the Nicaraguan leadership has declared a state of emergency under which the media are censored and opposition political activity is restricted.

Many Sandinista officials are beginning to portray the move toward socialism as their only chance for survival in a hostile world.

"We have a revolutionary project that we have demonstrated over the course of three years to be a moderate project in the face of great difficulties and adversities," one official said.

"But what happens? We see more each time that our political will to develop our project is being sabotaged systematically from all sides.

"We are going to continue making efforts to maintain our project. But if we are put in a position where we . . . have to decide whether we survive or not as a revolution, then we are going to take the measures necessary to survive."

At rallies around the country to commemorate international Labor Day Saturday, members of the Sandinista National Dictorate addressed the new slogan adopted by Sandinista labor unions: "We will defend the revolution for the construction of socialism."

Interior Minister Tomas Borge, considered one of the most radical Marxists in the top Sandinista leadership, addressed a rally of more than 50,000 people in Managua's Plaza of the Revolution.

Borge charged that opponents of the government would soon form a "junta of treason" made up of numerous critics of the government, including Roman Catholic Archbishop Miguel Obando y Bravo. Obando, who, unlike the others, is still in Managua, subsequently denied any interest in political posts.

After reciting what one businessman later described as "this enemies list of the government," Borge told his audience, "They do not know where we are going."

As he paused a chant began to well up from the crowd: "Socialism! Socialism! Socialism!"

Borge, who carefully avoided the use of the word himself, said quietly, "Our hard-working people know where we are headed."

In the farming town of Esteli, where some of the hardest fighting against the forces of the Somoza dictatorship or Somocistas took place three years ago, Agrarian Reform Minister Jaime Wheelock declared that "Nicaragua is no longer divided between Somocistas and non-Somocistas.

"It is divided between revolutionaries and counterrevolutionaries," said Wheelock in front of a poster juxtaposing Marx, Engels and Lenin with Nicaraguan revolutionary heros.

There is speculation even among middle-ranking Sandinista officials that this cry for socialism might be a "trial balloon," as one put it, to test national and international reaction and possibly to gauge the strength of hard-liners in the front against more cautious elements in this collegial government.

Many Nicaraguan businessmen who have attempted to act as a moderating force on the revolution both economically and politically are pessimistic about their future here. But they said they still see possible openings for a brake on what appears to be the Sandinistas' rapidly accelerating radicalization.

Some suggested that the sudden move toward embracing communism was directed at currying Soviet favor on the eve of Ortega's trip without making an entirely solid public commitment to Soviet ideology.

Nicaragua is critically short of funds. According to Borge, its income has dropped $110 million this year.

Most U.S. aid was cut off in 1981 and West European support is waning.

Even as Ortega was visiting Moscow, another high-level delegation, headed by junta member Sergio Ramirez was touring Western European capitals in search of aid and political support, news services reported.

Where are are you going to get the money to back this socialist project?" asked one businessman. "Our hope is that they will not get the money in Moscow and they will have to turn back to us."

The Sandinista leadership is being pressured from all sides, and not just economically.

The radicalization of the revolution's rhetoric during the last few weeks comes as U.S.-orchestrated pressures on the government have shown little sign of letting up and attempts to begin serious negotiations between Managua and Washington foundered as each accused the other of lacking serious interest in the talks.

Meanwhile, an open division within the upper ranks of the Sandinista hierarchy has emerged as a blow to the government's confidence if not actually its hold on power.

Eden Pastora, who as Commander Zero was a widely acclaimed hero of the insurrection against dictator Anastasio Somoza, announced in Costa Rica last month that he would lead a movement to oust the current Sandinista leadership.

Several non-Sandinista politicians who originally backed the Sandinistas, and who were named on Borge's list, have apparently decided in recent months that there is no future for civic opposition to the Sandinistas and are reportedly now in self-imposed exile.

Pastora is depicted as the Sandinista Front's first traitor. After weeks of denunciations of Pastora, the Sandinista leaders apparently have decided he should be made a nonperson and, as Borge put it, be written out of the revolution's history as Cain might better have been written out of the Bible.

One high Sandinista official said privately that the leadership here is concerned that Pastora will be a "useful tool of imperialism" and is capable of "any kind of craziness."

The official said reports that the state security department is keeping 600 suspected counterrevolutionaries under constant surveillance are "fantasy-like."

But the official added, "It is difficult for 10 Nicaraguans to get together to conspire without one of them being against the conspiracy. We know who conspires here, even some functionaries with whom we are still patient."

Asked about the call for movement toward socialism and the Soviet Bloc being orchestrated through the Sandinista trade unions, the official said, "In my judgment the workers in this country are seeing that there are no possibilities of coexistence in the framework created by the imperialist American policy in this region."