Fannie Mae and Freddie Mac are giving the cold shoulder to a White House-backed effort to encourage Americans to make their homes more energy efficient. The initiative, called Property Assessed Clean Energy, or PACE, aims to eliminate the high upfront costs that have kept homeowners from making cost-saving energy retrofits on their homes. Under the program, property owners borrow money from their local government to pay for the retrofits, repaying cities over 15 to 20 years through a special assessment that is added to their property-tax bills. Local governments fund the programs by selling municipal bonds to investors