President Jose Napoleon Duarte said today that he would meet again with El Salvador's left-wing rebels if Nicaraguan President Daniel Ortega would simultaneously talk with the guerrillas battling the Sandinista government.

Duarte's offer, unveiled in a series of interviews with American journalists, appeared designed to embarrass Ortega at a time when the U.S. Congress is considering whether to aid the Nicaraguan rebels, diplomats and Salvadoran politicians said.

The Nicaraguan government has said it will not negotiate with the Nicaraguan guerrillas, known there as counterrevolutionaries, or contras. If Ortega rejected Duarte's proposal, as expected, then the Nicaraguan leader would be in the position of refusing to seek a negotiated settlement in his country while Duarte seemed to be willing to work for one in El Salvador.

There was no immediate comment from the Nicaraguan government, but Hector Oqueli, of the Salvadoran rebel alliance, said the left rejected Duarte's offer.

U.S. Ambassador Edwin Corr said Duarte's "statesmanlike approach could be a major step toward bringing peace to the region through internal and external dialogue."

Duarte said he had not discussed the proposal in advance with the U.S. Embassy, and he phoned Corr on the subject in the middle of an interview with two reporters. The U.S. Embassy, however, was known to have been aware of the outlines of Duarte's plan on Saturday.

Duarte said he was sending a letter to Ortega today making the offer. "I am proposing to him a simultaneous dialogue. That means that he sits down with his opponents . . . and I sit down with mine, both at the same time," the president said.

Duarte did not say what he would do if Ortega rejected the proposal, but he indicated that there had to be two meetings or none at all. He reiterated past complaints that the Sandinista government provides supplies and logistical help to the Salvadoran guerrillas, and said: "I don't think I'm going to resolve the problem in El Salvador unless the problem is solved in Nicaragua."

Diplomats and others suggested the proposal was aimed at Congress as it considers the aid issue. They said Duarte had shown little interest in reviving talks with the guerrilla movement. The last session was on Nov. 30, 1984.

Duarte acknowledged that there had been no change in position either by himself or by the Salvadoran guerrillas that would increase the likelihood that progress could be achieved in talks. The rebels have rejected Duarte's condition that any settlement of the civil war here should be in accord with the nation's 1983 constitution.