Mr. LaHood said the department took notice of the company’s problems after an accident in California last year in which three people were killed. Since then, he said the department had discovered other safety issues with the company’s vehicles, and has met with engineers from Japan.

“We told them, ‘we’re going to call you out on this.’ They stepped up and they did the right thing, and we applaud them for doing this,” he said. Mr. LaHood said the department would help the company find a solution. “We’re going to get to the best safety that’s possible. They want to manufacture cars that are the safest for people to drive.”

Mr. LaHood said Toyota had figured out solutions to the problem on some of its vehicles. He recommended that owners immediately take their vehicles to dealers, and said the company would either fix them or find a way to provide other transportation while it found a solution.

Analysts in Japan have raised concerns for some time that Toyota’s rapid growth in recent years was overstretching the company. Toyota’s president, Akio Toyoda, has himself berated the company for excessive confidence, which he said had set the company up for a painful fall in the global economic crisis. He said last year that Toyota was “grasping for salvation.”

“We have had fears for quite a while now that Toyota lacked the human resources and production capacity for such rapid expansion. By chasing numbers, they were becoming seriously outstretched,” said Masahiro Fukuda, manager of research at Fourin, a global automotive research company based in Nagoya, Japan. “Many of us weren’t surprised over the big recalls; we were more surprised that it took Toyota so long.”

Other analysts faulted Toyota’s zealous pursuit of efficiency and cost-cutting. “The same parts were used here, there and everywhere, on major models,” said Koji Endo, managing director at Japan Advanced Research, a Tokyo-based research organization. “That’s very efficient, but very risky. If the part turns out to be faulty, you suddenly have a problem on your hands involving millions of cars.”

Now, halting its factories could have a “tremendous impact” on Toyota’s bottom line, especially if the interruption drags on, Mr. Endo said. “Toyota will have to change the design of the gas pedal, get relevant approvals, set up production, then exchange parts for millions of cars on the road, cars sitting at dealerships and cars they were assembling at their factories,” he said.