The United States yesterday accused Cuba of directly contributing to violence in El Salvador by sending weapons and leftist insurgents into the country to try to topple the civilian-military junta backed by the United States.

The charge was made by Carter administration officials who sought congressional approval to supply military equipment worth $5.7 million to El Salvador's ruling junta.

The accusation of direct Cuban involvement came one day after the assassination in El Salvador or Archbishop Oscar Romero, a popular figure and nominee for the 1979 Nobel Peace Prize. There was no suggestion that Cubans were involved in the killing of the archbishop.

Romero himself had recently written President Carter asking him not to supply more military aid to the ruling junta until it succeeded in stopping the violence that has racked El Salvador for many months.

However, Secretary of State Cyrus Vance said yesterday that the United States still plans to give military and economic aid to El Salvador, noting that the country's rulers recently have taken steps aimed at "healing" the country's wounds and divisions, and that "the junta has been making progress . . . especially in land reform."

Vance condemned the assassination as "appalling, saddening and tragic."

Administration officials testified yesterday that American intelligence believes Cuba is using the territory of Honduras, neighbor of El Salvador, to ship men and arms for use against the Salvadoran junta. The United States also has evidence that Cuba has been training Salvadoran guerrillas for a matter of years, and is sending them back to fight through Honduras, officials said.

"The Hondurans believe, our intelligence agrees, that their territory is being used as a conduit for men and weapons into El Salvador by insurgents with Cuban support," said Franklin Kramer, deputy assistant secretary of defense.

"Cuban influence on El Salvadoran and Honduran leftist organizations is long-standing, and there are clear indications the Cubans are assisting these groups in their attempt to overthrow the current government of El Salyador," Kramer told a House subcommittee.

His charges were echoed by John Bushnell, deputy assistant secretary of state. Both appeared before the House foreign operations subcommitee to request $46 million in military and economic aid for Honduras and El Salvador.

El Salvador's civilian-military junta has enacted a series of sweeping economic and land reforms with U.S. support and about $50 million in American economic aid.

"There is evidence that mountainous and sparsely populated areas of Honduran territory are being used for the illegal smuggling with Cuban support of insurgents and weapons into El Salvador," said Bushnell.

Both officials notes the close ties between Castro and Central American communist leaders, and said Cuba has most to gain from political violence and instability in that region.

Bushnell stressed that, in the wake of Romero's murder, Washington will continue supporting the ruling junta, "which is committed to basic economic and social reforms and to the improvement of human rights."

Bushnell told the subcomittee that the United States will not become military involved in El Salvador. "We will not use military force in situations where only domestic groups are in contention," he said.