"HAMP, despite its lofty goals, has not yet been able to contain the foreclosure tsunami," the center's Diane E. Thompson said in written testimony presented to the Senate Banking Committee.
The Obama administration has acknowledged some of the criticism.
"There appears to be substantial variation among servicers in performance and borrower experience, as well as inconsistent results in converting trial modification offers into actual trial modifications," Geithner and Donovan wrote in a letter earlier this month inviting mortgage servicers to meet with the administration. "We believe there is a general need for servicers to devote substantially more resources to this program for it to fully succeed and achieve the objectives we all share."
The servicers, meanwhile, contend that they are doing their part.
"The servicers that have signed up to participate in the program are taking their obligations very seriously," said Jeannine Bruin, a spokeswoman for GMAC, one of more than two dozen mortgage servicers, including Bank of America, CitiMortgage and Wells Fargo, that take part in the administration's program.
Bruin told ABCNews.com that GMAC had beefed up staff and staff training to address homeowner requests for help. GMAC officials, she said, were working "nights and weekends" on loan modifications.
"Can the program be improved and enhanced? I'm sure it can be," she said, "but it's not for any lack of effort for our part."
For now, homeowners like the Pedro and Lucy Gomez are turning to third parties for help.
Lucy Gomez was laid off last year and now the couple are facing foreclosure on their Elgin, Ill. home. They attended a workshop Friday held by the Neighborhood Assistance Corporation of America, a group that helps homeowners obtain loan modifications from mortgage servicers. The group recently kicked off a 10-city tour to meet with and counsel local homeowners. (Watch coverage of its first stop, a workshop in Cleveland, here.)
The Gomezes hope that NACA will help them work out an affordable loan modification with their mortgage servicer, GMAC. Pedro Gomez said he had no luck appealing to the company on his own.
GMAC said that while the company could not comment on specific customer cases, there could be "a logical explanation for why" Gomez didn't qualify for the modification he wanted.
Bruce Marks, the head of the Neighborhood Assistance Corporation of America, said the association has successfully achieved loan modifications for homeowners by putting together modification agreements and sending them electronically to mortgage servicers for their approval.
But the government, he said, should be requiring servicers to do that work for themselves. "It is really outrageous that a nonprofit has to step into to fill the void," he said.
The GAO, in its report last week, said it's unclear when the government will have a system in place to address "noncompliance" by mortgage servicers.
The report prompted more government criticism, this time by Sen. Chuck Grassley, R-Iowa.
"This report heightens my fear that Treasury will give out billions of dollars without ensuring the spending will work as intended," Grassley said in a written statement. "There's real doubt that this money will prevent foreclosures in the long term and help legitimately struggling homeowners. Once this money is spent, it will be gone. Unfortunately, Treasury isn't ready."