China issued strict regulations in September requiring automakers to sell large numbers of electric cars or plug-in hybrids in 2019 if they want to keep selling gasoline-powered cars. China then plans to phase out its generous electric car subsidies at the end of 2020, pushing automakers to figure out how to profit without them.

But Mr. Heizmann said on Thursday that even if China had not issued the regulations, its stringent fuel economy targets for 2020 could not be met without selling a lot of electric cars or halting the sale of all but the smallest gasoline-powered cars. The country will require each carmaker that year to sell cars with an overall average fuel economy of 47 miles per gallon.

The contrast with the United States is stark.

Republicans in the House of Representatives are pushing a repeal of the electric car tax credit, which could equate to about $200 million in the coming years, according to Congress’s Joint Committee on Taxation, or about 0.005 percent of the value of all of the tax cuts in the House bill. The Senate tax bill, which faces increasingly uncertain prospects, does not call for repeal of the electric vehicle tax credit.

If the House and Senate measures both pass, a House-Senate committee would then decide whether to include a repeal of the tax credit in the final legislation.

The Environmental Protection Agency began a review in August of fuel economy rules that is widely seen as preparation to loosen an Obama administration requirement that automakers double vehicles’ average fuel economy to 54.5 miles a gallon by 2025.

There are some differences between the American and Chinese fuel economy tests that make them not strictly comparable, however: The Chinese tests tend to show a slightly higher fuel economy for the same cars.

Automakers are also moving the production of parts to China for electric cars. Reliant on very large batteries from South Korea for its electric cars, G.M. is now moving to buy many of its batteries from Chinese suppliers, said Matthew Tsien, the executive vice president who oversees G.M.’s extensive China operations. That helps the company qualify for Chinese electric car subsidies that require considerable domestic content.

“We do see China being, in the near and medium term at least, by far the largest market for electric vehicles in the world,” Dan Ammann, G.M.’s president, said in an interview in New York this week. “But we believe ultimately that the whole world will go that direction.”