The biggest group among the latter is homeowners whose mortgages are under water, meaning they owe more than the property is currently worth. By the end of 2011, some 11 million homeowners were in that predicament — also known as negative equity — according to a recent report by data firm Core Logic. This group also happens to be a large source of home foreclosures.

Given that negative equity cases represent 22 percent of all outstanding home loans, that's a huge untapped market. It's also as much of an opportunity as it is a problem.

The Obama administration is taking another shot at it, having failed to accomplish much with its 2009 mortgage-aid program.

This month, Fannie Mae and Freddie Mac , the agencies that insure many mortgages, are rolling out automated underwriting in the latest version of the program for borrowers with no more than 20 percent equity, the Home Affordable Refinance Program , HARP.

The old rules required the property to be worth at least $75,000 for every $100,000 borrowed. The new version, dubbed “HARP 2.0” by the public, offers something close to a “no-doc” loan — employed borrowers don’t need to produce tax statements. They also don’t need a new appraisal, because this time there’s no ceiling on what lenders call LTV, loan to value.

Sound familiar?

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