Following new and domestically embarrassing revelations of Argentina's role in covert operations against the leftist government of Nicaragua, military leaders have assured protesting officials here that Argentine Army personnel have been withdrawn from Central America, according to government sources.

Both government and military officials here concede that some sectors of the Argentine military do not always act in accordance with official policy and that some Argentines may still be working with right-wing groups that are trying to overthrow the Sandinista government in Nicaragua. But the officials describe these men as mercenaries no longer backed by the Argentine Army or government.

"We have been told the people pulled out," a ranking civilian government official, who asked not to be named, said in an interview. "Now, if there are mercenaries who went there and decided they wanted to stay, we cannot control that."

Argentine military leaders consistently denied, even to their civilian colleagues, any activity in Central America. But such activity is believed to have begun in late 1979, within months of the overthrow of Nicaraguan dictator Anastasio Somoza by Sandinista guerrillas. Sources here and outside the country, as well as numerous published reports, have detailed Argentine covert support for exiled soldiers of Somoza's defeated National Guard who have vowed to throw out the Sandinistas by force.

The exiles have operated primarily from camps inside Honduras, launching harassment raids across the Nicaraguan border. According to informed sources in Argentina, Honduras and Washington, as well as within the exile groups themselves, some Nicaraguan exiles have received military and intelligence training in Argentina.

At the same time, Argentine personnel -- as many as several hundred by some accounts -- were sent on covert training, support and intelligence missions to Central America, primarily to Honduras but also to Costa Rica, Guatemala and El Salvador.

Argentina's activities coincided not only with foreign policy aims of the previous government here but also with a U.S. policy of support for anti-Sandinista groups. President Reagan last year authorized financing for the assistance of "friendly" third countries in a CIA covert action program against Nicaragua.

The apparent Argentine move to scale down its involvement in Central American operations is part of a dramatic shift of its official foreign policy following the Falkland Islands conflict with Britain last spring. Argentina -- which formerly perceived Central America's conflicts in East-West terms and supported U.S. policies -- has moved in recent months to strengthen its ties with Cuba, Nicaragua and the Nonaligned Movement, which backed its claim to the Falklands.

Reversing years of thinly disguised hostility, Argentina recently signed a trade agreement with a visiting delegation of the Sandinista government, offered financing for imports of Argentine products and backed Nicaragua's recently successful bid -- strongly opposed by the United States -- to join the United Nations Security Council.

At the same time, ranking officials in the Foreign Ministry, which is dominated by civilians, have privately pressured military leaders to end any involvement in covert activities directed against the Nicaraguan government or against the flow of arms to leftist insurgents in El Salvador.

In a videotape recording of unknown origins released publicly last month in Mexico, a self-described defector from the Argentine operations, Hector Frances, related in some detail the little-known Argentine activity and its command organization.

Although there was little public reaction to the tape, Frances' allegations caused both anger and embarrassment within the Argentine government, officials said. They privately confirmed that Frances attended an Argentine military school and appeared to have been associated with the activity in Central America, but they insisted he was a mercenary and never a regular member of the Army.

According to several government sources, following the release of the Frances tape, a ranking Foreign Ministry official met with President Reynaldo Bignone to demand information.

Bignone told the diplomat, Carlos Muniz, an Argentine official at the United Nations, that no Argentine Army personnel were now working covertly in Central America, according to one reliable source. The president also made the same assurance recently to a visiting Nicaraguan economic official, another diplomatic source said.

The timing of the Argentine withdrawal remains unclear to officials and diplomats here. Some civilian officials said that all Argentine officers left the region during or soon after the Falklands conflict, which lasted from April 2 to June 14. But other officials said it appeared that the withdrawal may have taken place in phases and that some operatives may have been ordered out only recently. Several officers are still in Honduras on an official basis as advisers or instructors, and reports there some months ago estimated that 35 Argentines were on the scene then.

Foreign Ministry officials now say the Nicaraguans appear eager to accept the change in Argentine policy and to overlook the past Army operations. "They see it as a closed chapter, something that happened in the past," said one official who has talked with Nicaraguan diplomats. "I think they are anxious to rebuild relations with Argentina. They see themselves as under a serious threat from the United States, a tightening ring, and they would like to have the support of Latin American countries."

Argentine officials now describe their country's active involvement in Central America as a misguided deviation from traditional Argentine foreign policy, which for decades shunned involvement in hemispheric conflicts as well as most U.S. regional initiatives.

According to present officials, the involvement by the military in Honduras began after a 1979 meeting of U.S. and Latin American defense chiefs in Colombia. Previously, Argentina's military government had been a strong ally of Somoza.

Military leaders were angered by evidence that the Sandinista movement had associated with exiled leaders of Argentina's leftist Montonero guerrilla movement, which Argentine military and paramilitary were still battling in 1979 in a bloody internal campaign, according to military sources.

Leopoldo Galtieri, who became Army commander in December 1979, two years before taking over as president, was a strong advocate of Argentine action in the region, according to diplomatic and military sources. At one meeting of Army generals, Galtieri said his intention was for Argentina to fill the strategic gap he said had been left by president Jimmy Carter in fighting Central American communists, according to an officer who was present.

Goverment officials and diplomats say the Argentine force in Central America apparently included personnel from the Army's intelligence battalion, other training and command officers and paramilitary irregulars who had been used against leftist terrorists and other military opponents in Argentina.

While these government sources, who asked not to be identified, say military leaders support Argentina's new policy, some acknowledge that government authority has been fragmented by political upheaval and that military sectors occasionally seek to promote a parallel policy opposed to the official one.

Meanwhile, Nicaragua reported renewed fighting with hundreds of ex-guardsmen operating from Honduras and sent a protest note to the government in Tegucigalpa, according to Reuter.