While they stopped short of directly criticizing automakers, which the parts suppliers rely upon for business, they came down clearly on the side of stringent emissions rules. Tailpipe standards should “continue to make progress on reducing emissions and oil consumption while saving consumers money at the gas pump,” the groups said.

At stake is a measure that the Obama administration estimated would eliminate as much as six billion metric tons of greenhouse gas emissions and save consumers more than $1 trillion at the pump over the lifetime of the cars affected. Together, the nation’s vehicles now regularly emit more earth-warming gases than its power plants.

California, also a party to the talks over the Obama-era emissions rules, has been the most strident defender of stricter standards, drawing on its unique authority under the Clean Air Act to write air pollution rules that go further than those set by Washington.

The debate puts carmakers and their parts suppliers, two industries whose interests would seem to be intimately aligned, on opposite sides of this fundamental issue. The reason: Parts suppliers have a particular incentive to push for cleaner standards, experts say, because tougher emissions rules would spur automakers to fill their vehicles with new, more efficient technologies, and the parts makers would profit from developing that gear.

Nexteer Automotive, for example, makes steering systems that are powered by electricity and not the vehicle’s engine, greatly reducing fuel consumption. The company, which is based in Auburn Hills, Mich., had struggled financially before a surge in demand for fuel-saving technology under Obama-era emissions rules helped it rebound.

Nexteer is a member of the Motor & Equipment Manufacturers Association, which represents more than 1,000 auto suppliers. MEMA signed Thursday’s statement together with four other groups that represent auto suppliers: Advanced Engine Systems Institute, the Emission Control Technology Association, the Manufacturers of Emission Controls Association, and the Aluminum Association.

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In a sign of the sensitivity of the issue, Nexteer deferred to the industry’s group’s statement and declined to provide a separate statement on the issue.

“These suppliers are investing in technology for the next generation,” said Luke Tonachel, director of the clean vehicles program at the Natural Resources Defense Council. “And these standards are really important for providing that certainty these companies need to keep on making those investments.”

Clean vehicle technology directly supports nearly 300,000 American jobs, the N.R.D.C estimated in a report published last year.

The Environmental Protection Agency, which sets emissions standards for light-duty vehicles, faces an end-of-March deadline to decide whether to review the rules. The National Highway Traffic Safety Administration, which sets fuel economy standards, is also expected to release proposed rule changes in late March.

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