Martin Ennals, 64, the former secretary-general of Amnesty International who helped build it into a leading human rights group, died Saturday in Saskatoon, Canada, after a yearlong battle with lung cancer. Mr. Ennals led the development of the London-based group as a major international monitor of human rights during his tenure as secretary-general from 1968 to 198. In 1977, he accepted the Nobel Peace Prize on Amnesty's behalf. Born in England, he earned a degree at the London School of Economics in international relations. He was teaching human rights at the University of Saskatchewan prior to his illness.