Fannie Mae and Freddie Mac’s newly amended preferred stock purchase agreement with the U.S. Treasury requiring the companies to accelerate the rate at which they reduce their investment portfolios will have little immediate impact but will become more challenging to the GSEs as time goes on, analysts predict. The Treasury’s amended agreement calls for the GSE portfolios to be wound down at an annual rate of 15 percent, instead of the 10 percent annual reduction originally required of the two companies. The more aggressive 15 percent reductions will go into effect in 2013. Consequently, Fannie’s and Freddie’s portfolios must be reduced to the $250 billion target by 2018, four years earlier than initially scheduled.