Zambian President Kenneth D. Kaunda urged Chad and Libya to maintain the cease-fire they agreed to Sept. 11. Each side has accused the other of violating the truce in their territorial conflict. Kaunda spoke at a 4 1/2-hour meeting in Lusaka, Zambia, of an Organization of African Unity committee seeking to resolve the conflict. Nigeria proposed an OAU observer force to supervise the cease-fire. Five African presidents attended the meeting, including Chadian President Hissen Habre. Libya sent its foreign minister.