Lisbon — Police investigating the killing of a leading Palestinian moderate in southern Portugal questioned a young English-speaking Arab. Morocco's ambassador to Portugal said a Moroccan passport carried by the youth was false and that he was definitely not a Moroccan. Police are trying to establish a link between the Arab and shooting of Issam Sartawi, a special envoy of the Palestine Liberation Organization (PLO) attending a Socialist International congress. The Abu Nidal group, an extremist Palestinian faction expelled from the mainline PLO, claimed responsibility for the Sunday attack. PLO chief Yasser Arafat accused the Israeli intelligence service of complicity in the slaying. Israeli officials denied the charge.