Consumer delinquency rates are dropping at US retailers and banks such as American Express and Bank of America, signaling an incipient lending thaw that may spur economic growth. … With fewer tardy borrowers to worry about, banks are more likely to extend fresh credit to American consumers, whose spending makes up 70% of the economy. That may weaken Federal Reserve Chairman Ben Bernanke’s commitment to an “extended period” of low interest rates — once policy makers determine the European debt crisis no longer poses a risk to the recovery, said economist Stephen Stanley.