JPMorgan Chase & Co., Bank of America Corp. and four other U.S. lenders may face an additional $31 billion in costs beyond what they have already set aside for buying back mortgages by 2012, Standard & Poor’s estimated.

Total losses from repurchases by the banks, which also include Wells Fargo & Co., Citigroup Inc., PNC Financial Services Group Inc. and U.S. Bancorp., may amount to about $43 billion from 2009 to 2012, Vandana Sharma, an S&P credit analyst, wrote in a report today. The banks have accounted for about $12.4 billion so far, she said.

Fannie Mae, Freddie Mac and bond insurers such as MBIA Inc. are pressing lenders to honor promises to buy back mortgages if they’re later found to be based on inaccurate data. Known as representations and warranties, the promises cover defects such as inflated appraisals or misstatements about borrowers.

“The current disruption creates additional uncertainty for the banks at a time, when in our view, they were just beginning the process of clearing up the growing other real estate owned inventories on their balance sheet,” the report says.