The Obama administration announced new plans Wednesday to make it easier for up to 9 million people to rework or refinance their mortgages, as the White House began an aggressive effort to stabilize the housing market.

A central element of the plan would allow up to 5 million people to refinance their mortgages into more affordable products through Fannie Mae and Freddie Mac, according to a summary of the plan.

A total cost of the effort wasn't immediately clear, though it could eclipse more than $200 billion because of new commitments to the Fannie Mae and Freddie Mac.

(This story and related background material will be available on The Wall Street Journal Web site, WSJ.com.)

The Obama administration's plan has three main elements: an effort to help homeowners refinance; another effort to help stabilize the housing market through a $75 billion initiative aimed at reaching up to 4 million at-risk homeowners; and a third element that aims to drive down mortgage rates.

Fannie Mae and Freddie Mac, which are privately held companies under government control, figure prominently in the plan. The government said it would increase its limits on the size of Fannie Mae and Freddie Mac's portfolios to $900 billion each up from $850 billion. Treasury also said it would increase its funding commitment to both companies "to ensure the strength and security of the mortgage market and the help maintain mortgage affordability."

Treasury also plans to increase its preferred stock purchase agreements with the companies to $200 billion each from $100 billion each.

"The increased funding will provide forward-looking confidence in the mortgage market and enable Fannie Mae and Freddie Mac to carry out ambitious efforts to ensure mortgage affordability for responsible homeowners," Treasury Secretary Timothy Geithner said.

The previous level was set when the companies were taken over by the Bush administration in September. Allowing the companies to buy or guarantee riskier loans could give them a bigger role in stabilizing the housing market but it could also expose them to heavier losses in the coming months.

The White House summary says its plan wouldn't help speculators, and instead would be aimed at keeping "hard pressed homeowners" in their homes. They also said they are working on "clear and consistent guidelines for loan modifications," which many have argued are necessary to speed up the process of making loans more affordable.

Fannie Mae and Freddie Mac will use the new guidelines for the loans they own or guarantee.

All companies receiving government money "will be required to implement loan modification plans consistent with Treasury guidance," the summary said.

The plan includes multiple incentives to prod servicers to modify loans. Servicers can receive an up-front payment of $1,000 for each eligible loan modification that meets certain criteria.

For a loan to qualify for modifications, lenders would need to bring the monthly mortgage payment down to 38% of a borrower's monthly income. The government would match further reductions in the interest rate down to 31% of a borrower's income.