WASHINGTON (Reuters) - U.S. industrial output grew strongly last month while producer prices fell at the sharpest rate in 1-1/2 years amid tumbling energy prices, according to reports suggesting healthy, noninflationary growth. U.S. factories, mines and utilities boosted production by a more-than-expected 0.8 percent in December, leading to a 4.1 percent gain for all of 2004, the best annual showing in four years, a Federal Reserve report showed on Friday. Separately, the Labor Department said producer prices dropped 0.7 percent last month, a sharper-than-expected decline and the biggest since April 2003. Prices were also well contained when excluding volatile food...