Anxiety surrounds Tuesday's Federal Open Market Committee (FOMC) meeting as the central bank's year-long mortgage-backed securities (MBS) purchase program nears its scheduled March 31 close, opening the door for mortgage rate increases and surprising market fluctuations. The Fed spent billions of dollars on MBS guaranteed by Fannie Mae, Freddie Mac and Ginnie Mae weekly for the past year, topping out its portfolio at $1.25trn. As the program ends, investors and analysts are speculating that mortgage rates could rise - and rise fast. "It's a trillion-and-a-half-dollar check that won't be there as the Fed withdraws from the market," said Pimco's Bill Gross in a recent interview. "How that affects the markets, I just don't know. I'm not eagerly anticipating the answer, but I think it holds some surprises in 2010 - not just in mortgage securities but stocks as well. We could miss the money, put it that way."