The nation's top auto safety regulator says an immediate recall of all Takata air bags wouldn't provide significant safety benefits and could exceed the government's legal authority.
National Highway Traffic Safety Administration chief Mark Rosekind also says a total recall would strain the replacement parts network and increase uncertainty for consumers.
Takata's air bag inflators can explode with too much force, hurling shrapnel at drivers and passengers.
At least 10 people have died worldwide and 139 have been hurt.
Rosekind made his remarks in a letter to Senator Bill Nelson of Florida.
Nelson has urged the agency to recall all Takata inflators.
So far 14 automakers have recalled 24 million U.S. vehicles to replace the inflators.
It's the largest automotive recall in U.S. history.
