Doctors amputated the lower legs of one of two teen-agers who survived a blizzard on Oregon’s Mt. Hood that killed nine others. Giles Thompson, 16, returned after the one-hour surgery to the coronary-care unit at a Portand hospital and showed signs of improvement. “It was a difficult decision to make but it was either amputation or his life,” said Dr. Leo Marx. “His arms and legs look good at this time and his family is with him,” said hospital spokeswoman Barbara Hood. Meanwhile, the condition of the only other survivor, Brinton Clark, 16, or Portland, continued to show improvement.