The Obama administration unveiled new measures Friday aimed at getting lenders to reduce the principal balances on problem mortgages and to refinance "underwater" borrowers who owe more than their homes are worth with government-sponsored loans.

The initiatives are part of an escalating effort to buoy the housing market - and an acknowledgment that more steps are needed to prevent a fresh wave of foreclosures from swamping it.

One provision will allow many unemployed homeowners to get three months to six months of reduced mortgage payments while they look for a job.

The most significant change to the $75 billion program helps underwater borrowers. It would encourage banks to reduce the principal on loans in default, and by refinancing troubled loans into Federal Housing Administration-backed mortgages.

With the changes announced Friday, the administration hopes its Home Affordable Modification Program will meet its target of helping 3 million to 4 million homeowners avoid foreclosure through 2012.

To date, just 170,000 people have gotten permanently lowered mortgage payments under the year-old program - which barely puts a dent in the projected 10 million to 20 million foreclosures expected in the next three years.

"It's really important to recognize we're not going to stop every foreclosure," said Diana Farrell, deputy director of the White House's National Economic Council. "It wouldn't be fair, it would be too expensive and we probably wouldn't succeed, in any case, because many people got into homes that they simply cannot afford."

The administration has resisted a move to slash principal on underwater mortgages, fearing it could encourage some borrowers to fall behind intentionally - sticking taxpayers with the bill.