BY KEVIN G. HALL
 Herald World Staff

 BUENOS AIRES -- A murder investigation in Buenos Aires that may implicate former Chilean dictator Augusto Pinochet also promises to shed light on an unresolved 1976 car bombing in Washington, which remains the deadliest act of international terrorism in the U.S. capital.

 The car bombing killed former Chilean Foreign and Defense Minister Orlando Letelier and his American aide Ronni Moffitt.

 In a rare interview, Argentine Judge María Servini de Cubria said this week that she expects to return to Chile within months to formally interrogate Pinochet about a
 September 1974 bombing in Buenos Aires that killed former Chilean armed forces commander in chief Gen. Carlos Prats and his wife, Carmen.

 SIMILAR

 The assassination of Prats, Pinochet's predecessor, was strikingly similar to the Sept. 21, 1976, car bombing on Washington's Embassy Row. Servini confirmed that she is exchanging information on the Prats murders with the U.S. Justice Department in its probe into the Letelier bombing.

 Servini and many other investigators think the same people committed both crimes and suspect Pinochet was involved.

 Pinochet, 85, was medically exempted from prosecution in Europe last year for murders that occurred during his bloody rule from 1973 to 1990. He faces charges in Chile of covering up murders and kidnappings that happened shortly after his U.S.-backed coup, and he is expected to be exempted from trial there on medical grounds.

 Last week, Argentine courts upheld the legality of testimony obtained by Servini in Chile, clearing the way for her to seek interrogation of Pinochet there.

 Even if Pinochet is freed from trial on medical grounds, Servini's investigation will continue. ``If Pinochet cannot be extradited because of his health, then at least we can bring to Argentina the others who committed these acts, the intellectual authors,'' she said.

 After interrogations, Servini put in requests to Chile to extradite Manuel Contreras, the former chief of Chile's feared secret police, known as DINA; his deputy, Brigadier Gen. Pedro Espinoza; former DINA members Raúl and Jorge Iturriaga; and other lower-level DINA members. Last November, Argentine prosecutors won a conviction and life sentence for Enrique Arancibia, a former Chilean secret policeman involved in the Prats bombing.

 NO EXTRADITION

 Contreras was indicted in the United States during the 1980s in connection with the U.S. bombing, but Chile refused his extradition while Pinochet ruled the country.

 Two Cuban exiles accused of carrying out the bombing were convicted of murder, but the verdicts were overturned on appeal, and they were acquitted in a new trial. An American who designed and planted the bombs confessed and turned state's evidence; he is now hidden away in a federal witness-protection program.
 Despite Argentina's high-profile pursuit of Pinochet and his associates, the U.S. Justice Department has been silent about its recent activities in the probe of the Letelier bombing. Justice investigators, through a Chilean attorney, interviewed 42 people in Chile early last year.