The scheduled start of an extradition hearing for Andrija Artukovic, 85, wanted by the Yugoslav government on charges of war crimes, was delayed by a federal magistrate because of a medical report that Artukovic was not competent to appear in court. U.S. Magistrate Volney V. Brown Jr. had earlier ordered Dr. David Hill, a cardiologist at the Long Beach Naval Hospital, to monitor Artukovic's mental condition daily during the hearings. Brown has ruled that the hearings will proceed only on days when Artukovic is competent. Psychiatric testimony has established that the former Croatian government official, accused of complicity in the murder of 770,000 Serbs, Jews and Gypsies during World War II, is competent on some days and mentally incompetent on others. The hearing was rescheduled to begin Thursday, depending on Artukovic's condition.