BERLIN, April 20 (JTA) — An ecumenical ceremony has been held near here to bury the remains of 32 Jewish and non-Jewish slave laborers who died during the final days of World War II. The remains were discovered recently by construction workers at the former site of the Heinkel factory, which produced airplane parts. During the war, the factory relied heavily on slave labor organized by the SS from the Sachsenhausen concentration camp. Officials of the memorial site at the former concentration camp said the victims came from France and Eastern Europe. During the 1962 trial of a former doctor at the camp, witnesses said the bodies of victims who died shortly before the end of the war had been burned. Meanwhile, more than 300 guests from France, Poland, Germany, Hungary, Denmark, the Netherlands and Ukraine gathered Sunday to commemorate the 53rd anniversary of the liberation of Sachsenhausen by the Soviet army.