WASHINGTON - As part of a broad effort to boost participation in its mortgage assistance program, the Obama administration will crack down on mortgage companies that are failing to do enough to help borrowers at risk of foreclosure.

The Treasury Department said Monday it will withhold payments from mortgage companies that aren't doing enough to make modified loans permanent. The largest of 71 participating mortgage companies will be monitored via daily progress reports.

The goal is to increase the rate at which troubled home loans are converted into new loans with lower payments. At the end of October, more than 650,000 borrowers, or 20 percent of those eligible, had signed up for trials lasting up to five months.

Getting homeowners to complete the process has been tough.

In early September, about 1,700 homeowners had finished the paperwork and received a new permanent loan. Treasury officials projected Monday that 375,000 homeowners would hit the deadline to convert to permanent modifications - or fall out of the program - by Jan. 1.

Under the $75 billion program, firms that agree to lower payments for troubled borrowers receive several thousand dollars in incentive payments for modified loans.

For details, call 1-888-995-4673 or visit www.makinghomeaffordable.gov.