DETROIT — Honda must do more to track down owners of 300,000 cars with highly dangerous Takata air bag inflators and make sure they are repaired, the nation’s top auto safety regulator said Wednesday.

Mark Rosekind, head of the National Highway Traffic Safety Administration, says the agency has talked to Honda about hiring private investigators to track down owners, sending notices in different languages, or even taking service trucks into neighborhoods to repair cars on the spot.

“There’s a whole series of things that we want to see,” Rosekind said at an auto industry parts supplier conference Wednesday in Detroit. “It’s just not happening fast enough for anybody.”

Tests show that air bag inflators in 313,000 older Hondas and Acuras have up to a 50 percent chance of rupturing in a crash and shooting shrapnel at the driver. NHTSA and Honda issued an urgent warning to the vehicle owners in June, but so far only 13,000 of the cars have been fixed.

The cars date to 2001 and have a type of inflator that is more prone to explode than others made by Takata. They are so dangerous that the government told owners not to drive them unless going to a dealer to get repairs done. Honda says replacement parts are available for these vehicles.