Despite previous instance that El Salvador has all the military equipment it needs from the United States, President Jose Napoleon Duarte made a pitch today for additional U.S. arms, including helicopters.

Duarte, the civilian head of El Salvador's governing Junta, said, however, that his country would continue to oppose the introduction here of any foreign combat troops, regardless of nationality.

Speaking at news conference after a 1 1/2-hour meeting with visiting U.S. Rep. Robert K. Dornan (R-Calif.), Duarte said he urged the congressman to help El Salvador obtain needed additional military and economic aid.

"I told the congressman that we need more military equipment to get the capacity to control our country," Duarte said. "We need more military equipment, including more helicopters, and the means to protect them."

U.S. Embassy officials said later, however, that no specific detailed shopping list had been presented to Dorman, who sits on the House Foreign Affairs Committee.

As a result of a special $5.2 million package from the Carter administration in January and an additional $25 million package in March from the Reagan administration. El Salvador has received 10 Huey combat transport helicopters, ground troop transports and infantry combat weapons and ammunition as well as 54 U.S. military advisers to instruct the Salvadoran armed forces.

Duarte and other junta members repeatedly have stated in public that El Salvador did not need any more military help and have added that even before this equipment arrived the Salvadoran armed forces had managed to defeat, or at least contain, the "final offensive" against the government launched in January with little success by the leftist guerrillas.

The Reagan administration, defending its program while being buffeted by charges that it could lead to an involvement reminiscent of Vietnam, has said recently that the current level of aid to El Salvador is sufficient.

As well as requesting this new, if undetailed military aid, Duarte indicated he would welcome more U.S. military trainers to instruct his troops as long as they had no combat role in El Salvador.

Dornan said that as a result of his talks with Duarte he would request that Congress double its economic aid to El Salvador. Duarte had expressed appreciation for the $62 million in economic aid given to El Salvador by Washington but said the country needed $200 million to $300 million.

At his press conference, Duarte brushed aside charges of government foot-dragging in its investigations of the murders of six U.S. citizens here since December and said the arrest last week of two Salvadorans in one of the cases was a significant breakthrough.

He confirmed U.S. reports that his government had succeeded in linking two prominent Salvadorans to the gangland-style slaying in January of two U.S. agricultural advisers and their Salvadoran host. But he stopped short of saying that Hans Christ, arrested by the FBI on a Salvadoran request last week in Miami, and Ricardo Sol Meza, arrested here April 4, would be charged with murder in the case. He said the actual charges were up to the courts and that "others" were involved.

Duarte also denied accusations by some U.S. diplomats here that an investigation of the murder in December of three American nuns and a lay worker, was being conducted at a "glacially slow pace."

He insisted that much has been established in the government's autopsy of the women, who had been shot to death and hastily buried alonside a road outside the capital. He said that they had been killed with G3 assault rifle ammunition dated 1953, five years before the Salvadoran government first received that type of weapon.

Some U.S. Embassy officials here believe that official Salvadoran security forces were involved in the women's murders.