Bank of America Corp. has an estimated $64 billion of mortgages that are six months or more delinquent, but have yet to enter foreclosure.

The number is twice the combined total of its four largest competitors. The loans are reviewed regularly as part of the $25 billion settlement over abusive foreclosure practices reached earlier this year by state attorneys generals and the five largest U.S. lenders, according to Bloomberg News.

The total is largely the result of acquiring Countrywide Financial Corp. in 2008 and highlights just how involved and lengthy it will be for B of A to work through the backlog as borrowers fall further behind and losses build for mortgage-backed securities investors.

The bank has begun loan modifications for many of the 275,000 homeowners who are at least 180 days behind but undoubtedly many will enter the foreclosure process.

B of A's portfolio of loans that are at least six months old and not in foreclosure accounts for 3.3 percent of all of the mortgages it services.

Citigroup Inc. has 1.1 percent of its loans in that category and JPMorgan Chase & Co., Wells Fargo and Ally Financial Inc. all have less than 1 percent, according to Bloomberg.

B of A has an estimated 930,000 loans that are at least 60 days delinquent, down from 1.5 million from the peak in January 2010, CEO Brian Moynihan said during an event last week.

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