Only 9% of eligible borrowers have received trial modifications under the Obama administration's ambitious effort to help struggling homeowners, according to data released by the U.S. Treasury Department on Tuesday.

Participating mortgage servicers, which receive hefty government payments for modifying loans, have had "uneven" success at rescuing borrowers, Treasury acknowledged, as a wave of foreclosures continues to pummel the U.S. housing market.

Bank of America and Wells Fargo Bank have started trial modifications for only 4% and 6%, respectively, of the eligible mortgages in their servicing portfolios, Treasury reported. Meanwhile, J.P. Morgan Chase Bank has started trial modifications for 20% of eligible loans.

"I think it's safe to say we're disappointed in the performance of some of the servicers," Treasury's Assistant Secretary for Financial Institutions Michael Barr said in a conference call with reporters. He insisted, however, that Treasury was encouraged by the program's overall results.

Barr declined to comment on any particular institution's performance, but said Treasury was pushing servicers to step up modifications. "We expect them to do more," he said.

The administration is feeling heat from lawmakers on Capitol Hill, as its foreclosure-prevention effort has failed to help as many people as expected. A major component of the plan devotes $75 billion of financial-rescue funds to pay incentives to mortgage servicers, borrowers and investors that agree to modify loans according to certain standards. When it announced the program in February, the administration said it would help as many as 4 million borrowers avoid foreclosure.

Officials say they are still on track to reach that goal. But so far, just 235,247 trial modifications have been started since the program was launched in March. Meanwhile, foreclosures are accelerating amid ongoing weakness in the labor market. U.S. foreclosure activity in the second quarter was up 11%, according to a July RealtyTrac report.

Treasury gauged program and servicer performance against an estimated 2.7 million borrowers that are 60 or more days behind on their mortgage payments. The pool of borrowers represents a rough snapshot today of borrowers currently eligible for the program, Barr said.

In a meeting at Treasury last week, participating mortgage servicers committed to more bring the total number of trial modifications underway to 500,000. Under the program, no incentives are paid out until borrowers are current on their modified loans for three months. Thirty-eight servicers, representing 85% of the U.S. mortgage market, have agreed to participate in the program.

To pressure servicers to improve their performance, the administration recently announced that Freddie Mac (FRE) will audit the applications of borrowers turned down from the program to see whether they slipped through the cracks. Meanwhile, Treasury will continue to publicize servicers' performance monthly.

Barr said Treasury will provide more details in the coming weeks on its program to incentivize investors to remove second liens and a separate effort to encourage alternatives to foreclosure, such as deeds in lieu of foreclosure.

Barr acknowledged that the dismal job market was making it even more difficult to help some borrowers. Treasury officials are mulling ways to help borrowers who have lost their jobs. Barr said the current program contained flexibility to provide short-term assistance to such borrowers.

"If there's no income at all to support the home mortgage, it's very hard to see how a loan modification will be long-term successful."

-By Maya Jackson Randall and Jessica Holzer, Dow Jones Newswires; 202-862-9255, maya.jackson-randall@dowjones.com