NEW YORK/SAN FRANCISCO (Reuters) – The U.S. Federal Reserve, facing this week its biggest policy decision yet under Chair Janet Yellen, puts its credibility on the line regardless of whether it waits or raises interest rates for the first time in nearly a decade. In a way it is a “damned if you do, damned if you don’t” situation for the Fed despite months of fine-tuning its message, dissecting economic data, and carefully building a consensus around the idea of a cautious and gradual “lift-off” from near zero rates towards levels it considers normal.