Sister Evelyn Mattern had two goals in mind as she stood vigil recently with a Protestant colleague in a gas mask, singing, "This Air is My Air!" at the North Carolina statehouse. Her short-term aim was to lend support to stricter regulations for the state's coal-fired power plants. Yet she also had a loftier, long-range objective, one increasingly shared by a wide array of activists: to transform the way Americans think about energy in time to stave off global warming. "I don't think we're going to have a mass movement anytime soon, but I don't think it takes that many …