THE UNITED STATES and Canada extended Tuesday for five years the North American Aerospace Defense Command Treaty to provide warning of an air attack against North America. . . . AN EARTHQUAKE measuring 6.6 on the Richter scale shook an area northwest of Anchorage, Alaska, late Tuesday, but there were no immediate reports of damage or injuries. . . . AN 8-YEAR-OLD filled a canister with gasoline Monday, ignited it and threw it on a 2-year-old, officials said in Los Ebanos, Texas. The toddler was hospitalized in critical condition with burns over 40 percent of his body.