"Just give us a little bit of time to take a look at it because they crunched a lot of numbers," Perino said, reflecting on the Congressional Budget Office's estimate on how much taxpayer money might be used to support the Federal Home Loan Mortgage Corp. and the Federal National Mortgage Association.

Perino also said the intention of the plan "is not to need any sort of federal taxpayer monies."

"Having the authorities in place that we've asked for, that we've asked Congress to pass, are important for market stability," she said.

U.S. Treasury Secretary Henry Paulson Jr. has asserted that there is no current plan in place for the federal government to purchase equity in either Freddie Mac (NYSE:FRE) or Fannie Mae (NYSE:FNM), although the plan calls for authorizing that.

The White House wants the authority to use the funds, but "we don't intend to use them," Perino said.