Analysts at the Royal Bank of Scotland said “the retained portfolio game is over” now that the Federal Housing Finance Agency has announced estimates on what Fannie Mae and Freddie Mac will ultimately cost taxpayers. Earlier this week, the FHFA said the government-sponsored entities could cost anywhere between $221 billion and $363 billion. The RBS analysts said their opinion is based on the FHFA assumption additions to retained portfolios are limited to delinquent loan purchases. In the banking giant’s weekly note on U.S. rates, analysts said once unlimited support from the Treasury Department expires at the end of 2012, another $247 billion may be needed to support the GSEs past 2013. RBS also said FHFA assumptions of a 5-point decline in asset-backed securities and commercial mortgage-backed securities “seems alarming if it is applied to senior as well as subordinated structures.” Analysts said the Federal Reserve‘s portfolio of agency debt and mortgage-backed securities declined by another $15 billion last week, bringing total declines to $97 billion since early August highs. Meanwhile the Fed’s level of Treasury securities has increased by $225 billion. Following its August meeting, the Federal Open Market Committee announced plans to begin reinvesting maturing MBS into Treasurys rather than back into MBS. Many expect Fed officials to boost Treasurys purchases after the FOMC meets again Nov. 2-3. “We have not seen any real selling of Agencies from foreign investors recently and think that most of this decrease was driven by declines in MBS holdings as investors switched” into Treasurys, the analysts said. Write to Jason Philyaw.