By Mark Felsenthal WASHINGTON, Jan 6 (Reuters) - Federal Reserve officials believed the U.S. economy would face 'substantial' risks even as benchmark interest rates were cut to near zero, with some worrying about the risk of deflation, minutes of a December rate-setting meeting released on Tuesday showed. At the Dec. 15-16 meeting, the U.S. central bank chopped overnight borrowing costs to a range of between zero and 0.25 percent, and with rates pushed to the floor, signaled it was ready to try to lift the economy by pumping vast amounts of money into distressed financial markets. 'Even with the additional use of ... (full story)