The  General Services Administration is replacing more than 5,600 of its least fuel-efficient cars and trucks with hybrids, the agency announced today. The move effectively doubles the federal government’s inventory of hybrid vehicles, which pair an electric motor with a traditional gasoline-powered engine. The new hybrids will be leased to agencies that are replacing vehicles this year. The Energy Department already said it will take 753 of the 5,603 new vehicles, bringing the total number of hybrid vehicles in the department to 888. The purchases announced today are in addition to the 3,100 hybrid vehicles agencies received last year as…