The tab for the proposed bailout of mortgage securities concerns Fannie Mae and Freddie Mac could run as high as $25 billion, according to an estimate released by the Congressional Budget Office.

The CBO said that the Treasury's plan to expand the companies' current credit lines of $2.25 billion, coupled with the Treasury buying stakes in both companies, if exercised, could result in the $25 billion cost over fiscal years 2009 and 2010.

The Treasury bailout is a part of a more sweeping housing legislation package that includes creating a new overseer for Freddie Mac and Fannie Mae, as well as a $300 billion mortgage-refinancing program.

Originally published in WebCPA.