The U.S. Treasury Department said today that it plans to wind down its $142 billion portfolio of mortgage bonds guaranteed by Fannie Mae and Freddie Mac by selling as much as $10 billion of the securities each month, Bloomberg said. Sales will start this month and will be subject to market conditions. When combined with principal repayments currently ranging between $3 billion and $5 billion a month, the sales may eliminate the portfolio in about one year, the Treasury Department said in a statement. Selling the holdings could raise as much as $15 billion to $20 billion in profit, according to a Treasury official who spoke to reporters on condition of anonymity.