The presidential administration’s plan to salvage mortgage finance giants Fannie Mae and Freddie Mac may cost tax payers as much as an average of $25 billion according to the Congressional Budget Office (CBO).

However, the CBO said that there are 50 percent chances that the Treasurery won’t need to intervene. Moreover, the CBO estimated that there are 5 percent chances that Freddie and Fannie's losses would cost the government $100 billion.

“There is a significant chance - probably better than 50 percent - that the proposed new Treasury authority would not be used before it expired at the end of December 2009,'' the CBO said in its report.

The CBO estimated the $25 billion possible cost as an average based on "the path of housing prices in the next several months." The report mentioned three possible scenarios in the near future: prices stabilize, grow modestly or decline steeply. The CBO released the report one day before the White House has scheduled the debate and vote on a rescue plan proposed by Treasury Secretary Henry Paulson last week.

Fannie Mae (Federal National Mortgage Association) and Freddie Mac (Federal Home Loan Mortgage Corporation), United States’ main providers of home loans, own or guarantee almost half of the $12 trillion in U.S. home loans outstanding. Paulson said the two GSEs are fundamental institutions in the nation’s capital markets today and are vital to emerging from the housing correction.

Fannie Mae fell $1.61, or 11 percent, to $12.52 at 9:35 a.m. in New York Stock Exchange composite trading. Freddie Mac dropped $1.25, or 14 percent, to $7.50.