Nearly 1 million U.S. homeowners have won permanent reductions on mortgage payments since the Obama administration launched its foreclosure prevention program in 2009, the U.S. Treasury said on Monday, only a fraction of the total it aimed to reach.

Some 11 million homeowners owe more than their houses are worth and the Home Affordable Mortgage Program (HAMP) has had limited impact on a housing market bogged down by foreclosures and tight lending conditions.

The administration initially projected HAMP would help up to 4 million homeowners stay in their homes.

The program, which provides financial incentives to mortgage servicers to rework loans, granted 23,374 permanent modifications in December, bringing the total to date to 933,327, the administration said.

Although the program has been widely criticized by Republican lawmakers for not being effective, the administration extended HAMP by one year through 2013 and expanded it to reach more indebted homeowners.

Treasury said 84 percent of homeowners seeking help through HAMP in the past 18 months received a permanent loan modification.

(Reporting By Rachelle Younglai; Editing by Leslie Adler and Andrew Hay)