As the Sandinistas begin building a new Nicaragua out of the ashes of the Somoza regime, the world is waiting to see whether this will become a second Cuba.

Four days into Nicaragua's new era, there are few clues as to where the country is headed. a civilian coalition government of wide-ranging ideology has been appointed.

Guerrilla leader Thomas Borges, the new interior minister, tells reporters: "I've never said i'm a Marxist. We are Sandinistas. We've said it 5,000 times. There are Marxists in our organization. There are Christians. There are Social Democrats in the Sandinista National Liberation Front."

But Borge has more than once espoused Marxist beliefs and he has traveled frequently to Cuba. He has met often with Fidel Castro and Cuba's Communist Party newspaper gives him front-page treatment as a freedom fighter.

The Sandinistas' roots and recent associations are intertwined with leftist and radical states as well as with democracies like Venezuela and Costa Rica. Now, the new government has said it wants ties with "all countries in the world that respect our independence.

But observers are watching for signs as to which of its wide range of donors and backers the Sandinistas, who are now governing Nicaragua, will repay by imitation.

It was not until nearly three years after he marched triumphantly into Havana that Castro told the world, "I will be a Marxist-Leninist until the last days of my life."

But by that time, the direction of the Cuban revolution was clear. Hundreds had been executed for complicity with the previous government, private property had been nationalized and there was a leftward realignment of Cuba's diplomatic relations and a sharp break with the United States.

Today, not only the United States but also some Nicaraguans are worried about which course Nicaragua's new government will choose.

"I am afraid that they will do all over the country what they did in Leon," one banker said. During six weeks of rebel occupation, that north central city was put on non-money rationing system to help conserve supplies and was ruled by Sandinista military commanders.

Others fear that with former President Anastasio Somoza gone as a uniting focus of opposition, the divisions that underpin Nicaraguan society will erupt into class war.

"The poor people talk about 'our revolution,' "said a middle class businessman, "and i'm afraid of what they mean by that."

But the vast majority of Nicaraguans appear overwhelmingly supportive of the new government. In its first week it has strictly adhered to previously announced plans. There has been no interference with private property except for the previously promised expropriation of property belonging to Somoza and his closest aides. Today the government expropriated 52 companies belonging to him, his family and his top supporters who fled the country with him.

Also as promised, the new rulers have so far spared the lives of thousand of Somoza's National Guard soldiers who accepted offers to surrender and take refuge in Red Cross and church centers.

"They will have to be investigated case by case," Interior Minister Borge said today. "The immense majority will be freed. Those of them who want to rejoin the army will be permitted to do so."

The key to the Nicaragua's immediate future will be the division of power between the left to moderate civilian junta and the guerillas who fought for its installation.

Most of the junta and its Cabinet come from a small circle of businessmen, intellectuals and professionals who have little personal following so far.

Unless their authority is quickly and forcefully consolidated, they run the risk of being rolled over and left behind by militants.

The Sandinista leaders already are national heroes. They lead a highly disciplined force of idealistic young rebels who have spent months, in some cases years, sitting in the mountains talking about a "new society."

While many are expected to drift back into civilian life, others identify themselves as professional guerrillas.

The Sandinista Front is formed of three factions of varied militancy, all openly espousing a leftist model for Nicaragua.

For now, their leaders maintain, they will leave politics largely to the civilians and Nicaragua will be reconstructed through democratic processes. Later, they say, when the people are better educated and politically more aware they will vote for and welcome sharper turns to the left.

How the rest of the world treats the new Nicaragua in these early days will doubtless play a large role in its political orientation. With long-held animosities toward the United States and its traditional support of Somoza, Nicaragua's new leaders are wary and are watching the Carter administration as closely as it is watching them.

So far, both sides have refrained from the name-calling that charaterized U.S.-Cuban relations in Castro's early days and in the view of most observers advanced the definitive break between the two countries and Cuba's alignment with the Soviet Union.

"We don't have any interest in the criteria of the Yankee imperialist," Borge said recently. "The junta government of national reconstruction has its plan. Analyze it."

As for the rest of Latin America Borge said, "We are surely going to be blamed, and a campaign will begin, for everything that happens in El Salvador, Guatemala, Chile, Paraguay and all of those countries dominated and exploited by criminal, despotic military governments. They are going to start saying that we are fomenting violence."

"The conditions that fomented revolution in Nicaragua are the ones that will foment revolution in all those countries. We will not export our revolution. But clearly we are guilty, and we must assume responsibility, for setting an example."

Meanwhile, Nicaragua presumably will establish diplomatic ties for the first time with the Soviet Bloc. The first post-war crowd of journalists to enter Managua with the Sandinistas last week included correspondents from Pravda, the Soviet news agency Tass and East Germany.

In an interview yesterday with NBC, junta member Sergio Ramirez said the new government also hoped for good relations -- and recontruction aid -- from "the Arab world."

The junta connection likely to be scrutinized most closely is that with Cuba. The Cubans acknowledge training some Sandinista fighters but they strongly deny that Castro provided either troops or arms.

Cuba today joined a number of Latin American democracies that have recognized Nicaragua's new government, United Press International reported after monitoring a broadcast by the Cuban news agency Prensa Latina. The broadcast, warned Nicaraguans that "threats against freedom have not disappeared," UPI reported from Mexico City.

Sandinista ties with Cuba go back to the 1960s when leaders of the then small guerrilla band went there for refuge, training and support that yeilded them few results in Nicaragua. In the early 1970s, there was more Cuban training. Some Sandinistas went to Algeria and other leftist Arab states where their instructors included members of the Palestine Liberation Organization.

The question of where the Sandinistas got enough guns to win a war has not been answered, but informed sources now talk more freely on the subject.

This was a small war fought largely with World War II and Korean War era weaponry on both sides.

Throughout the nearly two months of fighting, while Nicaraguan cities were being rocketed and bombed by Somoza's outdated air force, the Samdinistas were frantically but unsuccessfully trying to get surface-to-air missiles.

It was only after they badly lost a month-long skirmish last September that the guerrillas received significant foreign help, sources said. Among the main suppliers were Venezuela, whose former president Carlos Andres Perez was strongly anti-Somoza, and Panama's Omar Torrijos.

Panama supplied many of the small airplanes used by the Sandinistas during the past two months, sources said, as well as bombs intended to destroy National Guard headquarters and Somoza's bunker.

When they were dropped on Managua, only one of the bombs exploded

Panama and other Sandinista allies helped worked out arms purchases through both commercial and underground U.S. markets.

The sources said Sandinista representative made three visits to Cuba to ask Castro for weapons and that he turned them down. What Cuba did supply, however, was a wealth of contacts with arms-selling governments in Africa and the Middle East.

In the last weeks of the war, they said, Castro also permitted weapons supply planes from Europe, Africa and the Middle East to refuel in Cuba on their way to Panama and Costa Rica.

Contacts and logistical help were also provided by the PLO and European governments including Spain, the sources said. Money and moral support came from Europe's leading Social Democratic and leftist political parties.

Although they refused to supply details, the sources also maintained that at least two weapons flights from overseas, not including a PLO-chartered jet seized by authorities two weeks ago in Tunisia where "hijacked" by the U.S. Central INTELLIGENCE Agency. CAPTION: Picture, Junta member Alfonso Robelo gives a victory sign as Sandinistas parade. UPI