Rescuing mortgage giants Fannie Mae and Freddie Mac could cost as much as $363 billion over the next three years, more than double the amount spent so far, the agency overseeing the troubled companies said Thursday.

Estimates by the Federal Housing Finance Agency show that Freddie and Fannie could end up costing taxpayers $221 billion to $363 billion through 2013, it said in a report (pdf file). The estimates were the first the agency has issued since the two mortgage giants were rescued by the federal government two years ago amid the mortgage meltdown in late 2008.

Though banks and automotive companies have also received bailout money to help them weather the financial crisis, funds provided to Freddie and Fannie are on track to be the largest to emerge from the crisis, The Associated Press reported.

The estimates aren't predictions, said the agency's Acting Director Edward J. DeMarco in a statement. Rather, he said, "These projections are intended to give policymakers and the public useful snapshots of potential outcomes for the taxpayer support of Fannie Mae and Freddie Mac."

The projections are primarily related to further losses in Fannie and Freddie's book of business prior to their rescue, the agency said.