Interior Minister Thomas Borge has informally asked the United States to provide arms for the armed forces of Nicaragua's new revolutionary government.

The unexpected request is being interpreted by observers here as both an effort by the Sandinista leadership to arm itself against possible counter-coup attempts by ousted president Anastasio Somoza and a test of U.S. expressions of willingness to help the new government.

Borge said at a press conference last night that he requested U.S. military aid in a private meeting with U.S. Ambassador Lawrence Pezzullo yesterday.

Thomas O'Donnell, deputy chief of mission at the U.S. Embassy, said today that neither he nor Pezzullo would comment on what was said at the meeting with Borge, but O'Donnell added that "we're not denying" that Borge had made a request for U.S. arms.

The move to seek U.S. military assistance came as Nicaragua's new rulers took steps that demonstrated that the Sandinistas themselves - and not the five-member junta they named to govern the country - will keep control of Nicaragua's security apparatus at least for now.

Manuel Espinoza, the junta's official spokesman, said today that Borge was speaking to Pezzullo "as a leader of the revolution" but was not conveying an official request for U.S. arms from the junta.

Espinoza said, however, that the junta already had expressed its willingness to accept economic and military assistance from any government.

Borge, a leader of the Prolonged Popular War faction of the National Sandinista Liberation Front that overthrew Somoza, was named today, along with leaders of two other Sandinista $&(WORD ILLEGIBLE factions, to a three-member general command that will direct Nicaragua's new Sandinista People's Army.

Defense Minister Bernadino Larios, a former officer in the National Guard who is considered a moderate, was conspicuously absent at a press conference last night at which the new general command was announced. Larios' statement today that he knew nothing of Borge's request for U.S. arms was taken as further indication of his reduced role in military affairs.

In addition, it has been announced that a national police force, answerable to Borge in his position as interior minister, will be formed.

Borge, a cofounder of the Sandinista movement, has emerged as an increasingly powerful figure in post-Somoza Nicaragua although he is not a member of the junta.

At the press conference where Borge announced that he has requested military assistance from the United States, his statement was greeted by hearty laughter from the approximately 80 Nicaraguan and foreign journalists in the room.

Once it became clear that Borge was not joking, his request was interpreted in two different ways by observers here. The first was that the Sandinista leadership, afraid that Somoza partisans inside and outside the country may be planning a counterrevolution, need arms and are willing to take them from whatever country can provide them.

The second interpretation was that the Sandinistas are testing the intentions of the United States toward the new revolutionary government. A U.S. refusal to provide arms - in contrast to the military support it gave the Somoza dynasty for decades - would make it far easier for the new government to accept arms from Cuba for other anti-American sources while charging that the United States was behind efforts to topple the new government.

Luis Carrion said that Maj. Pablo Emilio Salazar had issued a communique in Miami saying he was organizing a 7,000-man army to invade Nicaragua.

Salazar, known as Commandante Bravo, led the National Guard forces that held off a 1,000-man Sandinista army in the key southern front during the civil war. Carrion also said the Sandinistas had reports that Tachito Somozo, Anastasio Somoza's son, was in neighboring Honduras trying to organize an army there.

Carrion said it was urgently necessary to create a regular army to defend the revolution and the government in case of attack from pro-Somoza forces inside and outside the country.

In announcing the formation of the new army general command - to be composed of Borge, Carrion and Humberto Ortega - the Sandinista leadership stressed that the irregular guerrilla force and the thousands of teeanagers who took up arms almost on an ad hoc basis to defeat Somoza, would not be enough to guarantee the future of the revolution.

"We must organize, organize, organize," Ortega said, "to create this great Sandinista Peoples Army." He and other Sandinista leaders refused to say how big they expect the army to be, or when they expect its first units to be formed. They were even less specific about their plans for the new national police force.

But they made clear that they, rather than the defense minister or the junta, will keep control of the country's new security apparatus for the forseeable future. They refused to discuss what political role the new army and police force might have.

They said that the new Nicaragua would have obligatory military service.

The Sandinistas also addressed another problem that has become increasingly acute. They called on the "people's military militia" - the groups of teen-agers who joined the fight and new continue to man roadblocks throughout Managua - to turn in their guns and return to their neighborhoods.

Carrion said that some of these armed teen-agers had taken the law into their own hands and had even committed criminal acts.

"They should not believe that they won liberty under the red and black [Sandinsta] colors to do whatever they want," he said. "What is meant as a service to the revolution can prejudice the revolution.

"The city is full of checkpoints that are keeping people from their normal activities," Carrion said. "Those who man t e checkpoints are well-intentioned but they hurt what we are trying to do. We are trying to get the country back to normal."