Decree Number One of Nicaragua's new government junta authorized legal action seeking former president Anastasio Somoza's extradition. Number Two wiped the Somoza name from public buildings and Number Three expropriated all property of Somoza and those who fled the country with him.

Those initial and highly popular laws established, the Government of National Reconstruction must now settle down to the business of running a country whose economy is destroyed and whose army, legislature, court and electoral structures it has abolished.

As the first successful Latin American revolution since Cuba, won by guerrilla fighters whose leadership is openly leftist, and in some cases Marxist, Nicaragua is well aware that the world is watching it.

In building a new society here, the five-member guerrilla-appointed junta has stated that its aim is to be democratic. But at the same time, it will have to balance the widely disparate interests of the guerrillas and the poverty stricken masses who expect an as yet undefined "people's government," with those of a conservative middle class and the hundreds of anti-Somoza businessmen, professionals and moderate politicians who anticipate no great changes in their lives.

After three days under their new government, Nicaraguans seemed content merely to walk about freely in the streets again and to begin to repair their war-damaged homes. Sandinista troops patrolled the streets andmaintained occasional roadblocks to check for auto registrations and illegal arms.

With several thousand Sandinistas now in the capital, following the arrival here of guerrilla columns from throughout the country, their presence is overwhelming. But in contrast to their National Guard predecessors, the guerrilla soldiers are less obtrusive and seem to have won at least initial popular approval by being courteous and unfailingly cheerful.

On a much larger scale, the big questions concerning Nicaragua's future remained. Among them are when the junta will hold promised elections and what will be done with the thousands of National Guard soldiers now in makeshift jails or designated refugee centers.

So far, there are few answers. Various junta spokesmen, both before and after the new government's installation, have proposed presidential elections intwo, three or four years. Most, however, refer vaguely to some time in the future when the country is "stabilized."

As for the soldiers of the previous government, while there is no indication that they are being mistreated, their fate is still undetermined.

According to a basic junta program issued Friday, the Sandinista National Liberation Front will be the foundation of Nicaragua's new army. As promised in earlier negotiations, "soldiers and officials of the National Guard who have demonstrated honest and patriotic conduct in the face of the Guard's corruption, repression and selling out" or who deserted to fight against Somoza, will be permitted to join.

Those prohibited from military service include "soldiers found corrupt or guilty of crimes against the people." At the same time, a military draft of undetermined length and numbers has been instituted.

Nearly 4,000 National Guard troops have taken refuge in Red Cross, church or embassy centers as part of a cease-fire agreement. Hundreds of others captured during the war, along with some Nicaraguans accused of spying for the former government, are being held in "Sandinista military police offices" here and in other cities.

While no one in the new government seems to feel that dealing with the soldiers is an immediate problem, some tension continues as small groups of renegade guardsmen and paramilitaries have attacked Sandinista patrols in the past several days.

Last night armed men in two trucks fired at the Camino Real Hotel, where the new government has established its informal residential headquarters. The attackers fled after a 20-minute shootout in which two Sandinista soldiers were wounded.

In its first three days in office, the junta has issued a number of decrees aimed at maintaining public order, an "emergency law" designating certain state powers for dealing with food shortages and war-destroyed institutions, and a "fundamental statute" outlining the projected structure of its government.

The laws project the new government as highly moralistic, concerned about state security, politically liberal in a social democratic mold, and most interested in trying to bring some order to the postwar chaos.

Decrees published yesterday authorize prison sentences of from three to 10 years for refusing to obey the cease-fire or trying to reinstate the Somoza regime, "committing acts that attempt to submit the nation to foreign domination," or revealing state secrets relating to defense or matters of foreign policy.

Lesser punishments of from several months to two years of impressed service on public works projects are prescribed for illegal possession of arms, "scandalous drunkenness," drug addiction, prostitution, and the vaguely worded crime of issuing "verbal or written expressions that intend wounding popular interests or taking away prestige from the conquests achieved by the people."

To administer this interim system of penalties, which is intended to complement the existing criminal code, another decree establishes "special emergency tribunals" in each provincial capital with teams of three locally selected judges.

While tribunal members already have been appointed in many parts of the country, few of the courts appear to have begun operation.

The junta's most pressing concerns are housing, feeding and finding employment for many of the country's 2.4 million people while it figures out Nicaragua's future.

According to one diplomatic report, Nicaragua is now undergoing "the worst economic crisis in its history," far surpassing a devastating 1972 earthquake that destroyed most of Menagua.

The country's agricultural system, which supplies nearly 80 percent of Nicaragua's income, is seriously disrupted.

After 18 months of insurrection resulting in destruction of much of the country's industry, the inflation and unemployment rates are at disastrously high levels. Cotton, Nicaragua's biggest cash crop, which provides work for more than 100,000 family heads, went unplanted this year, and the coffee crop has not been picked.

To establish a representative government until elections are held, the junta program calls for a 33-member Council of State composed of representatives of different anti-Somoza organizations that are nearly equally divided on both sides of a political line whose center is liberal.

Within the Council, the Sandinista National Liberation Front is allotted six members, as is the United People's Movement, a coalition of students and labor groups allied to the guerrillas.

One member each is alloted to four separate labor federations, to marginal political parties such as the Social Christians, and to other larger members of the moderate Broad Opposition Front, an anti-Somoza political coalition.

The Superior Council of Private Enterprise, Nicaragua's principal business and industrial federation, is allotted six council seats. The national university and clergy associations each have one member. No seats are authorized for Somoza's Liberal Party.

The council will be responsible for rewriting the Somoza constitution and electoral law. It can initiate legislation, pass it by majority vote and submit it to the junta for possible amendment, and can veto junta decrees by vote of two-thirds of its membership.

Yesterday, the junta appointed seven members of a new Supreme Court. As with Cabinet choices announced last week, the Supreme Court appointees are a mixture of active and passive Somoza opponents whose politics run from liberal to militant. CAPTION: Picture, Sandinista rebel leader is tearfully reunited with wife, two sons in Managua. UPI