By Ben Klayman DETROIT, Oct 22 (Reuters) - U.S. safety regulators on Wednesday expanded the number of vehicles in the United States that may be affected by recalls for potentially defective Takata Corp air bags that could spray shrapnel at occupants. The U.S. National Highway Traffic Safety Administration (NHTSA) said in a statement the number of vehicles from 10 automakers covered by recalls this year and in 2013 is now 7.8 million, up 28 percent from the 6.1 million announced on Tuesday.