“We are not quite sure what Apple is prepared to do,” Friedrich Eichiner, the chief financial officer of BMW, said during a meeting with a group of reporters in Frankfurt. He said he thought Apple was still trying to understand the implications of getting into the car business.

“Financially they are very strong,” Mr. Eichiner said. “They could do it.”

Luca de Meo, head of sales and marketing at Audi, another Volkswagen unit, said it would be out of character for Apple not to build its own vehicle, if it decides to get into the car business. “The Apple style is the ability to do software and hardware at the same time,” Mr. de Meo said in an interview.

The traditional carmakers’ big advantage is that they have already mastered the formidable complexity of manufacturing vehicles that are reliable, comfortable and safe. But it is becoming more feasible for a newcomer to outsource vehicle manufacturing the same way that Apple outsources production of iPhones. And the outsourcer wouldn’t necessarily be in China.

One company already working with Google is ZF, a large German auto components supplier that in May completed an acquisition of TRW, a company based in Michigan that provides auto electronics such as airbag systems. TRW has been working on sensors and other hardware for self-driving cars.

Stefan Sommer, the chief executive of ZF, said the company would be able to produce a Google-branded car along with two or three other partners supplying components that ZF can’t, such as sheet metal body parts. “We would be a partner in that, for sure,” Mr. Sommer said in an interview.

But he said ZF could not work with Apple under the conditions it now imposes on suppliers. ZF sees itself as an innovator, not just a supplier. In Frankfurt, it displayed a car with electrically powered wheels that allow the car to turn 360 degrees almost on its own axis. ZF could not agree to demands by Apple for exclusive rights to such inventions, Mr. Sommer said.

While Apple and Google pose a threat to traditional automakers, the mood in Frankfurt is not gloomy. Not long ago, analysts were predicting that the auto industry faced long-term decline. Surveys showed that younger people were less interested than their parents in cars and driving. But if Apple and Google are interested in the car industry, auto executives reason, cars and driving must be cool again.