All federal agencies in the Denver area will be powered in part by wind under the U.S. government’s largest contract to buy green energy, Energy Secretary Bill Richardson announced yesterday. The agencies will buy 10 megawatts of power annually from wind farms operated by Colorado utilities — enough energy to run 3,500 households for a year. Public Service Co. of Colorado, which already has 15,000 wind-power customers and a waiting list of potentials, is constructing more wind turbines. Richardson said the wind power will cost about 2 percent more than conventional power, but he argued that the higher price is offset by reduced pollution and lower dependence on foreign oil. Last week, Richardson ordered the Department of Energy to buy at least 3 percent of its power from non-hydro renewables by 2005 and 7.5 percent by 2010.