Two regional banking companies, Riggs National Corp....

Two regional banking companies, Riggs National Corp. in Washington and Columbus, Ohio-based Banc One Corp., announced plans to write off a big slice of their loans to developing countries. The moves follow Bank of Boston’s decision Dec. 14 to write off $200 million of Latin American loans, beginning a new chapter in the 5-year-old debt crisis in the Third World. By writing off loans, banks are for the first time acknowledging that many of them are uncollectable. The banks that have followed Bank of Boston’s lead have generally been strong regional institutions.