At least two Americans disappeared here during the military government's so-called "dirty war" against leftists and other dissidents, United States officials confirmed today.

The admission of the disappearance of two, and possibly three, Americans was a turnaround from previous statements by U.S. Embassy officials, who had maintained that no Americans were listed among the 6,000 to 15,000 people human rights groups list as disappeared, in most cases after detention by security forces.

Hundreds of foreigners are included in the lists. American officials have repeatedly said they have not become involved in current rights issues here because no Americans were believed to be among the disappeared persons.

Since President Reagan took office, officials here have opted generally for "quiet diplomacy" on human rights issues, despite often vocal criticism of the Argentine government from rights activists and fellow diplomats from Western Europe.

An embassy spokesman identified the missing Americans as Billy Lee Hunt, who was 28 at the time of his disappearance, and Jon Pirmin Arozarema, who was 26. Relatives of the two reported their disappearance to U.S. authorities in 1977, the official said.

The official said that at the time of the disappearances, "ample, appropriate and responsible representation was made to the Argentine government on both cases."

Officials here said the cases of the two men were forgotten after the beginning of the Falklands war last year, when staff members destroyed files in a general scaledown of the embassy staff and operations.

According to the Permanent Assembly on Human Rights, Hunt, an office worker, was abducted from his home in Mendoza, 660 miles west of here, on the night of April 8, 1977. Arozarema, an engineering student, was kidnaped from his home in Buenos Aires on the morning of April 30, 1977, assembly records show. Writs of habeas corpus for both were rejected in the local courts.

In Washington, a State Department spokesman said a third American, Toni A. Motta, a freelance journalist then 32, also was reported to have disappeared in Argentina in November 1980.