WASHINGTON – Just over 31,000 homeowners have received permanent loan modifications under the Obama administration's mortgage relief plan, a big setback for the government's embattled effort to stem the foreclosure crisis. Lenders blame the low success rate — only about 4 percent of the nearly 760,000 borrowers who have signed up — on borrowers who don't return the necessary paperwork to complete the process. Bank of America Corp., for example, had only completed 98 modifications at the end of November, far fewer than several smaller rivals. GMAC Mortgage completed 7,100, the most of any lender in the program, which was...