A retired Army intelligence official from El Salvador, who has been labeled a right-wing "terrorist" by the State Department and whose U.S. visa was revoked last month, gave a press conference five blocks from the Capitol yesterday despite warnings to the Immigration and Naturalization Service that he is in the country.

The press conference and subsequent luncheon, sponsored by the American Legion and the American Security Council, was attended by dozens of reporters, at least one congressman and a State Department representative sent to verify the Salvadoran's appearance.

State Department officials said they did not know how Maj. Robert D'Aubuisson entered the United States, since his name is listed as "ineligible" on the Immigration and Naturalization Service "lookout list" placed at all U.S. entry points.

They said his visa was revoked following his alleged participation in a Salvadoran coup attempt last month and death threats made by his organization against U.S. diplomats there.

At the press conference, at which he referred to U.S. Ambassador Robert White as a "proconsul" who sympathized with leftist guerrillas, D'Aubuisson urged strong U.S. backing of the Salvadoran military.

His organization, the Board National Front of El Salvador, also has been accused publicly by international human rights organizations, and in private by U.S. officials, of organizing the assassination of hundreds of Salvadorans in that country's bloody political warfare in recent months.

Several U.S. congressmen and human rights activists yesterday sharply questioned D'Aubuisson's presence here. They compared his apparent evasion of immigration officials to that of Chilean security agents who entered the United States in August 1976, although the INS had declared them "ineligible for entry" as dangers to the "welfare, safety or security of the United States.

Those Chileans were never aprehended. The men who entered under the posted names were later determined to have been part of a five-person Chilean secret police hit squad responsible for the September 1976 assassination of former Chilean diplomat Orlando Letelier in Washington.

Neither the State Department nor INS professed yesterday to be certain how D'Aubuisson got here, or where he is now. Despite his public appearance, the time and location of which was reported by United Press International several hours before it occurred, and his statement that he plans to visit several congressmen before he leaves the country this afternoon, U.S. government officials said they had been unable to apprehend him.

Yet, a reporter, told by U.S. officials that D'Aubuisson had stayed at Hyatt Regency hotel on his last visit here, and that he was believed traveling with Salvadoran businessman Orlando de Sola, telephoned De Sola's room at the hotel and was told that D'Aubuisson had stepped out but would perhaps be available for an interview today.

State Department officials, who would not speak for attribution, said INS had been informed Monday of D'Aubuisson's plans to visit Wahington. They said they had been told by human rights activists and believed he had arrived in Miami Monday on an afternoon commercial flight from Guatemala.

The officials said D'Aubuisson must either have entered the country under a false name or slipped through the INS bureaucratic net. They said notification of cancellation of his multiple entry visa had been sent to him in El Salvador last month along with a request to appear at the U.S. Embassy there. But the officials said he had not turned up, and notification had gone out to INS to stop him at any entry point and turn him back.

An official in the office of acting INS Commissioner David Crossland referred all questions concerning D'Aubuisson to the State Department and said INS was making "inquiries" into D'Aubuisson status and "allegations" of his presence in Washington. He said an investigation was being carried out by the local INS district office.

District INS director Kellogg Whittack said the first he had heard about D'Aubuisson was when a congressional aide called him yesterday at 10:30 a.m. to protest the presence of an illegal alien in the country.

Whittack said he referred the information to both the FBI and crossland's office.

"We knew nothing about any press conference or lunch," Whittack said, until about 3 p.m. "At that time we inquired" at the American Security Council headquarters at 499 S. Capitol St., where the event had been held, "and they said they had no knowledge of a press conference given by this individual.

"If we had received the information at the field office," he said, "we would have been acting immediately. By the time I received word" from the INS central office of when and where the press conference was scheduled, "it was already past that time."

Reporters present at the press conference said it apparently had been organized by MacKenzie Mccheyne, Inc., a public relations firm known for representing conservative Central American governments and organizations, and that Rep. Larry MacDonald (D-Ga.), was there.

MacDonald, along with Reps. Robert Bauman (R-Md.) and Sen. Jesse Helms (R-N.C.), has led congressional battles against the U.S. policy of supporting moderate groups against conservative forces in El Salvador.

Judy Bashore of MacKenzie Mccheyne said yesterday that D'Aubuisson would visit several congressmen during his stay here and that she would try to arrange an interview with him. She said, however, that the firm did not officially represent D'Aubuisson's organization but was "interested in everything that goes on" in Central America.

Whittack said last night that his investigators had visited the Hyatt Regency hotel, but that D'Aubuisson was not registered there. He said the Washington INS office had no posting of D'Aubuisson's ineligibility for U.S. entry. However, when told by a reporter that the State Department said he had entered through Miami, Whittack telephoned that INS office and later confirmed that such a ban existed, but that no one named D'Aubuisson had entered the country.

Reached by telephone at the Hyatt Regency, Orlando de Sola said that D'Aubuisson had a dinner engagement last night and was unavailable for an interview. He said he and D'Aubuisson who he insisted had entered the United States Monday in Miami under their own names, were leaving for home this afternoon, but that perhaps an interview could be arranged "the next time we're here.