Last Monday evening a blindfolded man, his arms tied behind his back, was escorted past the recently renamed palace of the Heroes of the Revolution here by seven or eight Sandinista soldiers, all of them armed and one of them with a kerchief mask tied over his face.

At the side of the building, within full view and earshot of Silvio Conrado, Nicaragua's new director of internal revenue, and me, the soldiers stopped the blindfolded man, unlocked the safety catches on their submachine guns and told their prisoner to run for it.

There was a short discussion and the man refused to move. Conrado cautiously walked toward the soldiers, talked with them briefly and then returned to his car. "They saw he just killed someone" nearby and "they plan to take him [in] for questioning," Conrado said. "I think it would be better if we get out of here."

What happened to the prisoner could not be determined. The odds are that he was not mistreated after Conrado intervened on his behalf. But there have been a number of other serious incidents here in recent weeks that illustrate the problems of the new government in maintaining order without a trained police force or a disciplined army.

Most of these incidents have come to the public's attention in the news pages of La Prensa, Nicaragua's most influential newspaper, which has insisted editorially that the new government take swift action to insure that the kinds of abuses that occurred during the years of rule under former president Anastasio Somoza not continue now that he and his National Guard are gone.

Interior Minister Tomas Borge has admitted some incidents that "violate our principles, including the death of ex-guard officer Lester Rene Hooker Coe while in the custody of a Sandinista guard.

At the same time, Borge has said it is "a miracle" that there have not been more reprisals against former members of the Guard and other Somoza supporters given the "accumulated hatred" that built up during the recent civil war.

Nonetheless, Borge and other new leaders know that the kinds of abuses that La Prensa continues to report almost daily are dangerous to the government's image. Brutality by the National Guard and the absence of an efficient and impartial judicial system were significant factors in turning many Nicaraguans against Somoza.

Within days after the Sandinista triumph July 20, Borge announced that a new national police force would be created under the Ministry of the Interior. The leaders of the Sandinista National Liberation Front announced that they would begin immediately to transform the guerrillas who won the war into a regular, standing army to defend against attack from abroad and to help maintain order inside the country.

When the new government came to power seven weeks ago, it was faced with two major security problems.

There were still members of the National Guard and armed Somoza sympathizers capable of attacking Sandinista patrols and government buildings in efforts to create chaos and the conditions for a possible counterrevolution. Although there are still some such attacks, this problem has been largely solved.

But a larger, more delicate problem for the new government was the thousands of armed teen-agers, called "militiamen," who fought against the National Guard in their own neighborhoods and who were reluctant to give up their weapons when the war ended.

The government had to weed out those who could not be trusted -- or who were potential criminals. Those who were more disciplined were integrated into what has become a semi-permanent national police force awaiting formation of a more professional one.

Thus, while thousands of teenagers were disarmed in the weeks after the war, hundreds more became policemen at command posts. At one in the easter section of Managua, Jose Arcadio Acosta, 25, has charge of 51 youths who provide police protection for nine neighborhoods housing about 40,000 of the capital's poorest citizens.

It is many of these armed militiamen who have caused the most problems in recent weeks.

Wednesday night, for example, four militiamen armed with .38-caliber revolvers, stopped a bus near the city of Jinotepe, 25 miles south of here, they robbed the driver and terrified the passengers. "How do you want to arrive at your house," the attackers shouted at the bus driver, "Dead or alive?"

La Presna reported earlier that a 12-year-old girl was shot and killed by a militiaman in Managua because he said her father was a Somoza sympathizer. Other murders have been reported that appear to have been committed by Somoza partisans against civilians who supported the revolution.

There have been, in addition, numerous cases reported by La Presna -- and acknowledged by the government -- of cars, houses and farms illegally seized by peasants or by common criminals who have taken advantage of the confusion for their own objectives.

Borge has warned that these illegal seizures will not be tolerated. An Aug. 23 communique recognized that soldiers and militiamen have approved of the land seizures and have committed crimes themselves.