National Guard forces made little progress in their efforts to rout rebels from eastern Managua today, despite almost continous daylight bombing and artillery attacks since Saturday.

Informed sources said that most civilians had managed to escape the several square mile zone that Sandinista guerrillas and their militia of neighborhood youths have held for more than two weeks. They said much of the zone has been destroyed, but that the rebels had suffered few losses. The rebels are said to be moving from house to house and hiding in specially prepared tunnels and shelters.

Early yesterday morning, a Sandinista aircraft flew over Managua and reportedly dropped ammunition and other supplies to the guerrillas.

The leftist Sandinistas have made few attempts to venture outside the eastern zone in the past week, and other parts are quiet except for occasional skirmishes at night.

A Sandinista offensive was launched throughout Managua June 9. A National Guard counterattack cleared the western part of the capital last week, although sources said the retreat of large numbers of local youths and their guerrilla leaders had been counted on to reinforce the eastern zone.

Rebel strategy appears to be to pin down the National Guard in Managua, where the government fears a direct assault on President Anastasio Somoza's bunker, while other guerrilla units fight for control of cities elsewhere.

In an interview last week, Somoza said the government would not move aggressively against rebel-controlled areas outside Managua until the capital was cleared.

The longer the guerrilas can hold out in Managua, however, the better appear their chances to consolidate control elsewhere.

Sandinista-controlled cities include Leon, the country's second largest city; Masaya, 20 miles south of here, and Diriamba in the southwest. Sources said today that the guerrillas also control Jinotepe, south of Diriamba; and the northern towns of Somotillo, Guasaule and Chichigaopa.

In Washington, President Carter's national secruity affairs adviser, Zbigniew Brzezinski, chaired a meeting of a White House special coordinating committee trying to formulate strategy for dealing with Nicaragua, U.S. sources said.

[The sources added that among those taking part were Vice President Walter F. Mondale, Defense Secretary Harold Brown, Deputy Secretary of State Warren M. Christoper and Adm. Stansfield Turner, director of the Central Intelligence Agency].

At the State Department, spokesman Hodding Carter said that, despite U.S. support of the Organization of American States' call for Somoza's ouster, the United States has no plans at present to break relations with Nicaragua and will continue to deal with the Somoza regime as "the government in place there."

[Brazil announced it was suspending relations with Nicaragua in keeping with the OAS move, a spokesman for the Foreign Ministry said, according to an Agence France-presse report from Brasilia.]

Meanwhile, members of the Sandinista-named provisional government again strongly denied claims by Somoza and the United States that Cuba has provided considerable assistance to the guerrillas.

"They can't support those charges with any evidence," one member, Sergio Ramirez, said in a telephone interview from Costa Rica.

Somoza has repeatedly charged Cuban involvement. One reported justification for a defeated U.S. resolution last week calling for intervention by an Organization of American States peacekeeping force here was alleged heavy Cuban involvement. Yesterday, Brown expressed Pentagon concern.

So far, Somoza has presented very little evidence of Cuban involvement and the United States has provided none. Both Cuba and the Sandinistas have denied the charge, and democratic governments in Latin American have expressed their own conviction that Cuba has kept arm's length from the Nicaragua war.

"I don't think Cuba was deeply involved in the Sandinista National Liberation Front," Jame Chamorro, spokesman for the U.S-backed Broad Opposition Front of anti-Somoza political moderates, said yesterday. Former Venezuelan president "Carlos Andres Perez told me he helped the Sandinistas so that Cuba wouldn't," Chamorro said.

"Peres said [Cuban President] Fidel Castro told him that the best help he could give the Sandinistas would be not to help them."

Moderate opposition politicians here have expressed concern that Somoza's charges, supported by the United States, showed no understanding of Nicaragua reality, of the overwhelming popular support the Sandinistas have. They fear that , should Somoza remain much longer, or the United States succeed in pressuring other Latin American government to remove support from the guerrillas, the charges could become self-fulfilling.

Neither the Sandinistas nor Havana have denied that a number of Nicaraguan guerrillas were trained in Cuba at least up until 1975. As the hemisphere's only communist government, Cuba has long served as a haven and sometimes as a supply center for leftist guerrillas throughout Latin America.

In an interview last summer, however, Castro told one U. S. reporter that while he supported the Scandinistas, he would make no large-scale effort to assist them materially as long as other countries in the hemisphere - including U. S. allies Venezuela and Panama - were serving that purpose.

At the same time, an informed foreign observer who supports the Sandinistas, said of the heavy bomb and artillery beating eastern Managua is taking: "If Cuba were sending equipment to help those boys, the people in there would not be dying like flies."

While the United States has referred only to alleged classified intelligence reports on the subject, Somoza has indulged in repeated escalation of the charges in attempts to gain support for his government.In a speech to the nation yesterday, he asserted, "The great majority of Scandinista weapons come from Cuba."

To support the accusations, Somoza has exhibited approximately 200 Belgian rifles made in the 1950s he said were captured from the Sandinistas. Somoza said the rifles were sold to the pre-Castro government of Fulgencio Batista. Other proof, Somoza had said, are approximately two dozens Soviet-made rockets his government has captured and repeated denunications of his regime over Radio Havana.

The vast majority of Sandindista armament, however, is U. S. and European-made - purchased on the black market, donated from sympathetic democracies or captured from the National Guard. Within the mongrel Sandinsita arsenal, the most prevalent communist-made weapons are a quantity of Korean War rocket launchers made in China, arch-enemy of Cuba and the Soviet Union.

While the United States believes the five-member provisional government chosen by the Sandinistas is too radical, it has now been recognized by both the moderate Broad Front and Nicaragua's largest private enterprise association as an acceptable alternative to Somoza.

Other Latin American governments have stepped up their assistance to the rebels as the United States becomes increasingly isolated from both Somoza and the Sandinistas.

According to government sources, an Ecuadorean aircraft with two tons of ammunition destined for the Sandinistas was seized yesterday by the military government in El Salavador. Sources said the plane was being flown by Costa Rican pilots and that bad weather forced it to land in El Salvador.

The sources said the plane was believed part of a well-established air bridge to ferry supplies to the guerrillas.

At the same time, the International Red Cross is attempting to establish its own air bridge of food and medical supplies to Nicaragua with charter flights from Miami.

"We need rice, corn, beans and cooking oil," a Red Cross official here said. With roads to northern agricultureal districts long closed by fighting, "little food is reachable in the country, and we have to be careful not to exhaust final supplies here." CAPTION: Picture, Using FAL and Galil rifles captured from Nicaraguan troops, Sandinista guerrillas defend position in Managua.