The head of US mortgage finance giant Freddie Mac will resign next year, the government said Wednesday in announcing changes at the top of the government-seized firm.Charles Haldeman, chief executive of Freddie Mac, "recently informed the board of his desire to step down some time in the coming year," the Federal Housing Finance Agency (FHFA) said in a statement.Haldeman has assured the board that he will remain as CEO until the transition has taken place, said the FHFA, which oversees Freddie and sibling Fannie Mae, bailed out in 2009 taxpayer-funded rescues.