A senior State Department official said yesterday that Roberto D'Aubuisson, the right-wing El Salvador political leader who has been banned from the United States since May, 1980, will be permitted "in the future" to come to this country and meet with U.S. policymakers.

Thomas O. Enders, assistant secretary for inter-American affairs, revealed this shift of attitude toward D'Aubuisson as speculation continued about whether the Reagan administration will be willing to support a new Salvadoran government in which the cashiered army officer has a major role or influence.

In Sunday's Salvadoran elections for a constituent assembly, D'Aubuisson's Nationalist Republican Alliance, known as ARENA, won 19 of the 60 seats. That makes him the potential kingmaker in the efforts of five rightist parties to form a provisional government that would exclude the centrist Christian Democratic Party, unofficially favored by the United States.

At a nationally televised news conference Wednesday, President Reagan refused to answer questions about whether he would continue military and economic support to a D'Aubuisson-influenced government. However, U.S. officials have been giving unmistakable signals to Congress and the public that it might be necessary to deal with a rightist Salvadoran government if it promises to pursue policies of reform and further democratization.

In an interview yesterday with the National Public Radio program "Communique," to be broadcast this weekend, Enders said he didn't "envisage any immediate meetings up here with any of the current leaders" in El Salvador's political maneuvering. But he added that "it would be quite normal in the future that we would meet here and elsewhere."

Asked specifically about D'Aubuisson, Enders replied: "In the future, absolutely, we would expect to see him and the others up here. I don't want to single him out. I don't think he would receive any different treatment than the others."

Enders' remarks represented a considerable shift away from the arms-length posture the United States had taken toward D'Aubuisson, who was described by former U.S. ambassador Robert E. White as a "pathological killer" and who has been linked repeatedly to incipient military coups and paramilitary terrorist activities.

In May, 1980, the Carter administration revoked his visa to the United States, and when he turned up here a month later, he was expelled. In March, 1981, Secretary of State Alexander M. Haig Jr. and other senior Reagan administration officials vehemently denied D'Aubuisson's public contention that U.S. officials had led him to believe they would not oppose a coup in El Salvador.

The administration, at that time, called D'Aubuisson's statements "pure fiction," stressed that he was not in contact with U.S. officials and made clear that the ban on him would continue.

Some of the charges against D'Aubuisson stem from papers confiscated by Salvadoran security officers after they surprised him at a meeting. White later told Congress the documents offered "compelling if not 100 percent conclusive evidence" that D'Aubuisson ordered the 1980 murder of Archbishop Oscar Arnulfo Romero.

Frederic L. Chapin, who temporarily took over the U.S. embassy in San Salvador after Haig fired White, attributed responsibility for machine-gun attacks against the embassy last year to D'Aubuisson.

At a Senate Foreign Relations Committee hearing yesterday, Sen. Paul E. Tsongas (D-Mass.) caused a ripple of laughter when he asked Rep. Robert L. Livingston (R-La.), one of the U.S. observers at the Salvadoran elections, if D'Aubuisson's reputation for violence put him in the same category as the leftist guerrillas fighting the government there.

Livingston replied, "The laughter in this chamber leads me to believe that the power of the press in this country is stronger than the truth." Livingston added that he suspects D'Aubuisson "has been painted worse than he probably is" and said he expects him to participate in the new government.

Everett E. Briggs, a deputy to Enders, did not mention D'Aubuisson directly in his testimony. But he criticized the tendency to call the ARENA party and other groups to the right of the Christian Democrats "right-wing" and asserted that ARENA includes "some very liberal and some moderate people."

The uncertainty about the new government's shape continued yesterday to push back progress toward talks between the United States and Nicaragua about ending Nicaraguan aid to the Salvadoran guerrillas. Nicaraguan Foreign Minister Miguel D'Escoto said in a telephone interview from New York that he had been waiting there for two weeks but had been continually put off by the United States.

D'Escoto said he would leave Sunday for a nonaligned-nations meeting in Kuwait and added that there could be no further movement on talks until his return to New York April 15.