Struggling homeowners who received loan modifications under a federal government program are defaulting on their mortgages at an alarming rate, according to a watchdog report released Wednesday.

The report from the special inspector general for the Troubled Asset Relief Program said the Treasury Department’s Home Affordable Modification Program, or HAMP, has failed to ensure that mortgage reductions are sustainable.

Home loans modified in the third and fourth quarters of 2009 are now defaulting at a rate of 46 percent and 39 percent, respectively. As of the end of March, more than 312,000 homeowners have defaulted on mortgages modified under HAMP, according to the report.

“This is a significant problem,” said Christy Romero, special inspector general for TARP. “When homeowners fall out of these modifications, all of a sudden they’re facing huge mortgage payments. If they can’t afford it, they’re going to get foreclosed on.”

The Obama administration created HAMP in 2009 as a lifeline for the millions of homeowners facing default in the wake of the housing bust. The program provided $75 billion to help lenders reduce borrowers’ monthly payments to 31 percent of their income.

At the time, the administration estimated that HAMP would help as many as 4 million homeowners avoid foreclosure. But the program has been plagued with delays and has faced criticism for not reaching enough struggling Americans.

Diane Cipollone of the National Fair Housing Alliance is still hearing complaints from homeowners about the pace of reviews and a lack of transparency in the denial process.

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