DON SIEGEL, a former actor who went on to direct such hits as "Dirty Harry" and "The Bodysnatchers," died over the weekend of cancer in Nipomo, Calif., at age 78 . . . A GAS EXPLOSION in South Africa gutted a central Johannesburg store early Tuesday, injuring the owner and 13 people in an apartment block above the premises, police said . . . REA E HOPPER, who oversaw the design of such diverse aircraft as Howard Hughes' famed "Spruce Goose" and the Apache helicopter that played an important role in the Persian Gulf war, died Friday of pneumonia in Santa Monica, Calif., at age 85.