The SunZia transmission line that would link sun and wind power from central New Mexico with cities in Arizona is just the sort of energy project an environmentalist could love -- or hate. And it is just the sort of line the Interior Department has been tasked with promoting -- or guarding against. If built, the 460-mile line would carry about 3,000 megawatts of power, enough to avoid the need for a handful of coal-fired plants and to help utilities meet mandated targets for use of renewable fuel.