People’s increasing willingness to abandon their own piece of America illustrates a paradoxical change wrought by the housing bust: Even as it tarnishes the near-sacred image of home ownership, it might be clearing the way for an economic recovery.

Thanks to a rare confluence of factors — mortgages that far exceed home values and bargain-basement rents — a growing number of families are concluding that the new American dream home is a rental.

Some are leaving behind their homes and mortgages right away, while others are simply halting payments until the bank kicks them out. That’s freeing up cash to use in other ways.

The U.S home-ownership rate has charted its biggest decline in more than two decades, falling to 67.6% as of September from a peak of 69.2% in 2004. And more renters are on the way: Credit firm Experian and consulting firm Oliver Wyman forecast that “strategic defaults” by homeowners who can afford to pay are likely to exceed one million in 2009, more than four times 2007’s level.

Stiffing the bank is bad for peoples’ credit, and bad for banks. Swelling defaults could also mean more losses for taxpayers through bank bailouts.

Analysts at Deutsche Bank Securities expect 21 million U.S. households to end up owing more on their mortgages than their homes are worth by the end of 2010. If one in five of those households defaults, the losses to banks and investors could exceed $400 billion. As a proportion of the economy, that’s roughly equivalent to the losses suffered in the savings-and-loan debacle of the late 1980s and early 1990s.

(click to play the interactive graph of Strategic Default)

The flip side of those losses, though, is massive debt relief that can help offset the pain of rising unemployment and put cash in consumers’ pockets.

For the 4.8 million U.S. households that data provider LPS Applied Analytics estimates haven’t paid their mortgages in at least three months, the added cash flow could amount to about $5 billion a month — an injection that in the long term could be worth more than the tax breaks in the Obama administration’s economic-stimulus package.

“It’s a stealth stimulus,” says Christopher Thornberg of Beacon Economics, a consulting firm specializing in real estate and the California economy. “The quicker these people shed their debts, the faster the economy is going to heal and move forward again.”

As the stigma of abandoning a mortgage wanes, the Obama administration could face an uphill battle in its effort to keep people in their homes by pressuring banks to cut their mortgage payments. Some analysts argue that’s not always the right approach, particularly if it prevents people from shedding onerous debts and starting afresh.

“The effect of these programs is often to lead homeowners to make decisions that are not in their economic best interests,” says Brent White, a law professor at the University of Arizona who has studied mortgage defaults.