AUTHOR ELLIOTT ROOSEVELT, who served his father, President Franklin Roosevelt, during World War II and later wrote a best seller about it, died Saturday at age 80 in Scottsdale, Ariz. The cause of death was not immediately disclosed . . . THE HEADS OF STATE of Uganda, Rwanda, Burundi and Zaire have agreed to form a military peace-monitoring force as a first step to end the almost monthlong civil war in Rwanda, official Radio Rwanda said Saturday . . . A MAN belonging to Sinn Fein was shot to death outside a friend's house in central Ulster, Northern Ireland. It was the 11th killing in renewed sectarian violence over the past week, authorities said Saturday.