This likable blonde dancer-turned-thespian gained international attention as the frazzled, clueless but good-hearted mother to a trying but adorable brood in Steven Spielberg's kidflick classic "E.T. The Extra-Terrestrial" (1982). As Mary, Stone (then billed as "Dee Wallace") managed to cope with the demands of work, single parenthood and first contact with alien life while maintaining a sense of humor. When the film broke all previous box-office records, she seemed a solid bet to become the movie Mom for modern America. But it was not to be. Stone remained a steadily working actress in some