The United States has begun overtures to younger officers in the National Guard in an effort to persuade them to stay in Nicaragua and maintain the force following the resignation of President Anastasio Somoza.

According to informed sources, the United States hopes that high-level officers identified with government corruption and repession will leave Nicargua with Somoza but that younger, "U.S.-trained" soldiers will "maintain the National Guard" as insurance "against communist influence" exerted by Sandinista guerrillas.

Although there now appears little doubt that the government will lose the war against the guerrillas, sources said, U.S. policy calls for breaking up the Sandinista army after the war and integration of some "moderate" guerrillas into a future armed force dominated by the National Guard.

Little support for this plan has been expressed among factions in the Nicaraguan crisis. One high-level official in the Somoza government today accused the United States of "trying to subvert" members of the government force.

While the Sandinistas have said they would allow certain "decent" National Guardsmen into their new government's army, they have adamantly rejected any plan for the perpetuation of the National Guard itself.

Among those National Guard officers who could be expected to remain in Nicaragua under a new government, few of those interviewed believed such a joint army would work.

The future of the Guard is one of the main issues to be worked out in negotiations among a guerrilla-backed provisional junta, the United States, other Latin American governments and Somoza.

Somoza has declared his intention to resign as soon as the United States assures him that the "institutionality" of the National Guard and his Liberal Party are guaranteed under a new government.

The provisional junta, based in Costa Rica, denounced foreign pressure to maintain the National Guard yeesterday. The United States, junta foreign minister Miguel D'Escoto said, "is trying to condemn us for something they think we might do." D'Escoto said the junta fears the National Guard is so hated in Nicaragua that concessions made to ensure its survival would weaken the junta's ability to exercise governmental authority.

The informed sources said they believed the National Guard's supply problem, plus "demoralization" of government troops, insured a Sandinista victory.

Heavy fighting continued today in several parts of Nicaragua.

While the National Guard has dislodged most of the rebel forces in the southern provincial capital of Rivas, sources said the guerrillas have cut land supply lines to the main National Guard column 30 miles south, near the Costa Rica border.

Sources confirmed that a National Guard force outside rebel-occupied Leon had fallen to the Sandinistas Saturday.

In June, the sources said, National Guard casualties totaled 1,100, including 220 killed. The guerrillas continue to describe their casualties as "light" but have released no figures.

Managua remains under National Guard control, although analysts said a concerted Sandinista attack from several directions could easily take the city.

The united States yesterday transferred a C130 transport plane and two helicopters from the Panama Canal Zone to an airstrip in Liberia, Costa Rica, 90 air minutes away.

U.S. officials said the aircraft are on alert for possible emergency evacuation of U.S. Embassy personnel and other American citizens still here.