The paramount Nicaraguan opposition group, which has claimed numerous commando raids against the Sandinista government, reportedly with covert U.S. backing, today announced a new political leadership designed to attract rival anti-Sandinista subversives and create a more palatable public image.

The announcement marked a public relations debut for the group, the Nicaraguan Democratic Force (NDF). Although well known to the press and public around Miami, it previously had maintained a technically underground status while seeking political support in this country. Its armed forces have operated from camps just inside Honduras, harassing Sandinista forces in Nicaragua with raids reportedly supported by the U.S. Central Intelligence Agency.

But the group has always had image problems, particularly among other groups of Nicaraguan exiles who have left the country since the Sandinistas took over, because many of its members were supporters of former dictator Anastasio Somoza or members of his National Guard.

The Reagan administration, according to U.S. officials, while openly opposing the leftist Sandinista government, has recognized the unpopularity of the former Somoza soldiers among most Nicaraguans -- even those who now are dissatisfied with the Sandinistas. In policy decisions taken in late 1981, the administration hoped to lend covert and overt support to anti-Sandinista forces that did not have the Somoza taint.

But these forces, principally led by former Sandinista hero Eden Pastora and former Sandinista government member Alfonso Robelo, both now disillusioned with the government and in exile in Costa Rica, have refused to join forces with groups like the NDF because of its Somoza ties.

Faced with the continued refusal by the Pastora-Robelo forces publicly to support them, the NDF leaders apparently tried with today's news conference to reach other anti-Sandinistas identified as opponents of the Somoza government.

"We open our arms to all those who wish to join us and express our patriotic intention of cooperating with any group which shares our objectives," the group said in a statement. "We ask the nations of the hemisphere that, just as they supported our first effort to free ourselves from dictatorship, they might now, convinced that our struggle is also their struggle, offer us their decided support in our effort to complete the patriotic task, so that Nicaragua can again be a republic."

Six new members of the NDF "directorate" were introduced, including:

Edgar Chamorro Coronel, a psychologist and investor; Alfonsa Callejas, a businessman who was a minister and vice president under Somoza but resigned in protest in 1972; Indalecio Rodriguez, a veterinarian who helped found the ruling Sandinista Front but later left in disgust; Lucia Cardenal, widow of murdered businessman Jorge Salazar Arguello; Marco Zeledon, former president of the Nicaraguan Superior Council for Private Initiative, and Enrique Bermudez, a National Guard officer who served as Somoza's military attache in Washington.

The other two on the eight-member directorate were not revealed for what Edgar Chamorro called security reasons. One was understood to be Steadman Fagoth, a Miskito Indian leader who reportedly has helped organize broad Miskito resistance to Sandinista rule in the undeveloped Zelaya Province on Nicaragua's Atlantic coast.

Bermudez, according to reliable Nicaraguan exile sources and an Argentine ex-intelligence officer now with the Sandinistas, has been the chief military leader of the guerrilla campaign against Nicaragua. According to reports from Washington and Honduras, the campaign has been backed by the United States with help from Argentine and U.S. advisers and cooperation from the Honduran Army of Gen. Gustavo Alvarez Martinez.

Bermudez refused all comment on his military activities in Honduras or Nicaragua. Chamorro, speaking for the directorate, cited the U.S. Neutrality Act in refusing to discuss NDF connections with guerrillas. The Sandinista leadership charges them with more than 50 killings in cross-border raids since July.

The Neutrality Act bars persons on U.S. soil from operations against foreign governments at peace with the United States.

A directorate member speaking privately said the new leadership is working to get rid of several former National Guard officers working with Bermudez, whom Pastora's group has specifically identified as unacceptable. These include, among others, Ricardo Lao, identified by exile sources as a former officer in Somoza's military intelligence. "They are on their way out, I think," the directorate member said.

He expressed hope that, with these officers most identified with abuses under Somoza gone, Pastora, Robelo and others in the Costa Rica-based Revolutionary Democratic Alliance, can be persuaded to join the NDF and make a united Nicaraguan opposition front more likely to gain public support in Nicaragua and the United States and more financial and diplomatic backing from the Reagan administration.

As part of the new effort, Jose Francisco Cardenal, one of the movement's early leaders, was not at today's news conference. Exile sources said he remains part of the movement but stayed out of the limelight because he had become too closely identified with rightist backers among the ex-Somoza backers living in Miami.

Bermudez, although a former National Guard officer and politically to the right, has not been singled out as particularly objectionable. Capt. Roberto Sanchez, the Sandinista Army spokesman in Managua, recently pointed out that Bermudez has never been identified with what the Sandinistas call "war crimes" committed under Somoza.

The military effort based in Honduras recently has come under increased control by the Honduran Army, which has increased border patrols and forced Nicaraguan counterrevolutionary guerrillas to move inside Nicaragua or shift their camps more deeply inside Honduras. It is not known whether this marked a permament change or a response to President Reagan's trip to the area last week. The move followed widespread reports in the U.S. press that the administration was helping organize the harassment raids.