The nation's four largest banks are holding $57 billion of seriously delinquent loans that they've been slow to move into foreclosure over concerns that the Federal Housing Administration, the government mortgage insurer, will refuse to cover the losses and hit them with damages, industry sources told American Banker. However, the banks -- Bank of America Corp., Citigroup Inc., JPMorgan Chase & Co. and Wells Fargo & Co. - have assured investors in the footnotes of quarterly filings that the loans are government-insured and therefore pose no threat to their bottom lines, even if they end up in foreclosure. What's more, the banks have used these supposedly ironclad government guarantees as a pretext for continuing to classify the loans as performing and for holding no reserves against them.