All told, the new measures are expected to cost about $50 billion. The White House was careful to stress that the money will come from funds already set aside for housing programs in the Troubled Asset Relief Program. There will be “no additional commitment of taxpayer dollars,” Michael S. Barr, an assistant secretary of the Treasury, said at the White House briefing.

Image A foreclosed home in Bridgeport, Conn. If its housing plan falls short, the Obama administration may have to start over yet again. Credit... Spencer Platt/Getty Images

Here is what the $50 billion is supposed to buy:

The simplest component of the plan involves assistance to unemployed homeowners. Mortgage companies will now be encouraged to reduce payments for at least three months and possibly six months while the homeowner pursues a new job.

To be eligible, borrowers must submit proof they are receiving unemployment insurance. The new payments will be 31 percent or less of their monthly income. The missing money will be tacked onto the loan’s principal.

A second and more complicated program is a requirement that mortgage servicers consider writing off a portion of a borrower’s loan to get it down to a more manageable level.

Borrowers in the government modification plan who owe more than 115 percent of the value of their home and are paying more than 31 percent of their monthly income toward the mortgage are eligible. The write-downs are to take three years, with the borrowers in essence being rewarded for making their payments on time.

The third major new program strays the farthest from the government’s previous approach. Borrowers who owe more on their homes than they are worth will get a chance to cut their debt — providing the investor or bank who owns the loan agrees.