NEW YORK — Newfound signs of stability in the housing market could still be threatened by rising foreclosures and slow efforts to stop them, according to two reports released Tuesday. The Standard & Poor’s/Case-Shiller index of 20 major cities showed the smallest monthly decline since June 2008. The index tumbled by 18 percent in April from the year before, but for the third month in a row it was not a record decline. Yearly losses in 13 metros improved compared to March. ‘It seems that some stabilization may be appearing in some of the regions,’ said David M. Blitzer, chairman of the S&P index committee. But rising foreclosures fueled by layoffs could derail a meaningful turnaround. The number of homeowners at least two months behind or in foreclosure jumped in the first quarter from the previous quarter, a Treasury Department report said Tuesday. Defaults from borrowers with good credit contributed to much of the increase in seriously delinquent loans, echoing data last month from the Mortgage Bankers Association. As the recession claims more jobs, borrowers in good standing are more likely to miss their mortgage payments. Efforts to modify home loans have been slow and […]