For almost two years, home foreclosures have swept the nation, spreading misery among once-buoyant families, spattering lenders with red ink and undermining efforts to restart the economy. But a bigger problem may turn out to be the millions of Americans who are still faithfully paying their mortgages, but on houses worth far less than before the bubble burst. It’s not that these homeowners will stop making their payments. It’s just the opposite – that they will keep doing it. How could that be a source of future trouble? Because, with home prices stagnant in much of the country, payments on mortgages that are underwater could absorb billions of dollars that might be used for other forms of consumer spending – a drag on family finances, the housing market and the overall economy.