Members of a provisional government named by the Sandinista guerrillas to replace President Anastasio Somoza said today they plan to move into Nicaragua and establish a capital within a week.

Sergio Ramirez, one of the five-member provisional body named last week, said in a telephone interview from Costa Rica that their government would be set up in Leon, Matagalpa or Rivas.

Leon is Nicaragua's second largest city. The Sandinistas have occupied Leon for two weeks and Thursday routed a final half-dozen National Guardmen from their garrison in the heart of the city.

While the guerrillas control the streets of Matagalpa, 80 miles north of here, they remain under heavy attack from government, air and artillery fire.

Rivas, the southern city that was the Sandinistas' original choice for a capital of "liberated territory" in Nicaragua, is still largely controlled by the National Guard as the rebels' southern offensive remains stalled near the Costa Rican border.

Alphonso Robelo, one of two politically moderate members of the leftist-dominated provisional government, said the fianl decision on when and where the government will be stablished would be made after t he group visits Panama.

Panama and Grenada so far are the only countries to recognize the group, three of whose members are in Costa Rica while two others are reportedly on battle fronts inside Nicaragua.

Several other nations, however, have broken relations with the Somoza government, including Mexico, Costa Rica and Ecuador.

Robelo predicted that additional countries would break with Somoza within days. "By next week, we'll be inside the national territory" and will ask for recognition, he said.

Both Robelo and Ramirez denied U.S. press reports, and charges within the Organization of American States, that the Sandinistas are being materially aided by Cuba in their war to overthrow Somoza.

"I know of no Cuban participation," said Robelo, 39, a businessman who heads the left-centrist Nicaraguan Democratic Movement. He is reportedly the member of the provisional government who is most acceptable to the Carter administration.

In speeches before emergency sessions of the Organization of American States last week, U.S. officials expressed concern over the supposed radical makeup of the junta and possible Cuban influence over a Sandinista government.

Ramirez, 37, said charges of Cuban aid were simply used by Somoza and then picked up by the United States to justify outside intervention by those opposed to a leftist government in Nicaragua.

Ramirez, an author and university professor one U.S. official described as "far too much to the left for the American public," called the charges "nonsense." He noted that Venezuela, which opposes both Cuban participation and Somoza, last week sent a diplomatic mission to Havana "to consult with Fidel Castro." Those talks centered on the position Venezuela and other Latin American countries have taken against not only outside intervention but also against any international call for somoza's resignation.

"Castro," Ramirez said, "supported that position." He added, "If Cuba had been giving the [Sandinistas] help and arms, we'd have won a long time ago."

Both Ramirez and Robelo said the provisional government has no plans to expand its membership, despite U.S. calls that it be broadened to include representatives from Somoza's political party and the National Guard.

In the only significant military development today, Guard sources confirmed that the small city of Diriamba, 30 miles south of the capital, has been taken by Sandinista forces after a three-day battle.

In Managua, house-to-house fighting continued in several of the poor neighborhoods where combat has centered for over a week. National Guard was reported to be dropping bombs from helicopters of Managua were in ruins. Most homes have been abandoned and scores of makeshift roadblocks blocked traffic. Poor residents carrying burlap bags could be seen picking through garbage and stripping the carcasses of burned-out automobiles amid the almost continuous crackle of gunfire.

At least two piles of bodies were seen today on the streets of the slum of Don Bosco. The bodies had been set afire to prevent disease.

Although Somoza confidently predicted Friday that the road from the city to Las Mercedes International Airport would be open by today, it remained under guerrilla control.

A Nicaraguan Boeing 727 jet with 11 passengers on board was diverted to Costa Rica on a flight from Miami to Managua today, and airport sources there said the pilot and copilot sought political asylum. The Nicaraguan pilot told police he landed his Lanica Airlines jet in Costa Rico because of the situation in Nicaragua.

The government radio today repeated urgent appeals for residents of four slum areas to "escape from the Communist terrorists" apparently in preparation for a National Guard counter offensive in those neighborhoods.

An official communique today ordered all civil servants to be on the job Monday, despite what the government called the "present circumstances" in "the Vietnam of America." Yesterday, the clandestine rebel radio station urged those workers to quit their jobs, warning that public buildings will be considered military targets.