U.S. worker productivity fell at its fastest pace in four years in the final three months of 2012, the government reported Thursday, but the decline was likely to be temporary as economic growth is expected to accelerate after stalling in the fourth quarter. The Labor Department said productivity - the amount of output per hour of work - fell at a 1.9 percent annual rate in the October-December quarter, the weakest pace since late 2008. Productivity rose at a 3.1 percent annual rate in the third quarter.