WASHINGTON (AP) -- Transportation officials are reviewing the "safety culture" of the federal agency that oversees auto recalls, a senior Obama administration official said Friday. The National Highway Traffic Safety Administration has been criticized by lawmakers and safety advocates for not acting aggressively enough regarding millions of vehicles with defective air bags or faulty ignition switches.

A special Transportation Department team is examining whether "we have the dial set correctly on risk management and our safety posture in general" throughout the department, especially at the safety administration, said the official, who asked that he not be named as a condition of briefing reporters. The safety agency is part of the Transportation Department.

The Takata building, an automotive parts supplier in Auburn Hills, Michigan, is a major supplier of airbags to automakers. (AP Photo/Carlos Osorio)

Announcements related to the review are expected in the coming weeks, the official said. The White House is expected to nominate a new administrator to run the troubled agency within the next two weeks, he said.

Further action also is possible involving air bag inflators made by Takata Corp., the official said. The inflators can rupture, ejecting shrapnel in a crash. Safety advocates say the problem has caused four deaths and multiple injuries. So far automakers have recalled about 12 million vehicles worldwide due to the problem, but recalls in the U.S. have been limited to vehicles registered in regions with high humidity. Millions more vehicles could be affected if the air bag recalls are extended nationwide, according to safety advocates.

No firm cause of the problem has been identified. Takata and the safety administration are investigating the impact of prolonged absolute humidity, which is a measure of the moisture content in the air, on chemicals that propel the air bags in a crash. They're looking into whether moisture in the air can cause the chemicals to explode with too much force, causing metal parts to fracture.

On Wednesday, the safety administration warned the owners of an additional 3.1 million vehicles to get their air bags checks repaired because of the potential danger to drivers and passengers. The agency has previously issued a warning covering 4.7 million cars and SUVs.

"The investigation is not over," the official said. "What has happened this week is an initial round of actions, but I wouldn't assume there wouldn't be future actions related to it."


Follow Joan Lowy on Twitter at http://www.twitter.com/AP-Joan-Lowy

© 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Learn more about our Privacy Policy and Terms of Use.