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.