A 16-year-old boy injured in a mountain climbing accident that killed nine friends has successfully scaled the physical and emotional obstacles caused by the tragedy. Giles Thompson, who was nearly killed when he and some classmates were caught in a snowstorm on Oregon's 11,235-foot Mt. Hood, said in a series of copyright articles in the Longview (Wash.) Daily News that mental attitude has had much to do with his recovery. "I don't think of myself as being disabled," he said. "You shouldn't let anything stop you. The mind is the most disabling part of the body." When rescuers found him, Thompson had a core body temperature of 86 degrees, which gave him about an 80% chance of dying. Thompson did live, but was in for months of tedious and sometimes painful treatment that included removal of the lower halves of both legs. He received a letter from Ted Kennedy Jr., now 25, who lost a leg to cancer when he was 16. Kennedy wrote: "Giles, no matter how grim things might seem now, a full, adventurous and challenging life awaits you. . . . You will be stronger-willed because you will have to fight for something, and you will be free-spirited because you will learn at an early age not to be troubled by things in life which have no consequence and things you cannot change." Thompson has returned to school, and last month he skied at a Colorado resort that has a program for the handicapped. "I don't think I really realize I've lost my legs. Maybe it's just too recent, maybe it'll hit me like a freight train, that I'm going to be like that until the day I die. It's so permanent. It makes you understand your own mortality."