THE UNITED STATES is on the trail of two leading suspects in the murder, in Washington in 1976, of former Chilean ambassador to the United States Orlando Letelier and an American colleague, Ronni Moffitt. Adding its own weight, it has passed on to Santiago a request from the District Court here to question the men who reportedly came to the United States on official passports and met with the Cuban exiles believed to have placed the car bomb that killed Mr. Letelier and Mrs. Moffitt. After some initial dissembling, the Chilean government acknowledged that passports indeed might have been issued to the two men, and it has asked for appointment of a judge to investigate the case. Chilean sources have identified the suspects, one supposedly an American with CIA connections, as members of an extremist group active in the coup that replaced the elected Allende government (which Mr. Letelier served) when the junta that still rules.

For the Chilean government, the risk is clear. Thorough and honest cooperation with the American inquiry could lead to its own doorstep, since it is widely believed that the junta itself organized the murder of Orlando Letelier to silence an effective and embarrassing critic. But a failure to cooperate could cost the junta the opportunity it craves for moral and political rehabilitation in the eyes of its own many disaffected citizens and in the eyes of the outside world. We applaud of Carter administration for making sure Santiago understands the stakes in the investigation of what may turn out to have been not only a horrible crime but also an officially inspired violation of American sovereignty. The responsibility must be fixed, no matter where the trail leads.