Heather Zichal, deputy assistant to the president for energy and climate-change policy, makes a forceful case for the need to slash greenhouse-gas emissions and boost the efficiency of cars and small trucks: The moves will cut America’s oil consumption, foster the nation’s energy independence, save consumers money at the pump and help revive domestic auto manufacturers.

What she doesn’t volunteer is that they will curb climate change.

The Obama administration is crafting two regulations — one targeting passenger vehicles, the other focused on heavier trucks and buses — that would do more to cut global-warming pollution than any other policy in the president’s time in office.

But that fact is barely mentioned as officials negotiate with automakers, environmentalists and others, particularly about the contentious car and light-truck rule due out in September.

“This rule fits very well within the broader framework of what we’re trying to do to make sure we have a healthy, robust domestic auto industry,” Zichal said of the proposed fuel-efficiency requirements.

Has the administration given up on climate change since legislation died in the Senate last year, as some advocates allege? Or has it simply rebranded the idea and its goals, as others complain?

Jonathan Lash, president of the World Resources Institute, said the administration runs a risk when it minimizes global warming’s public profile.

“I don’t blame the president for the failure of climate legislation, but I do hold him accountable for allowing opponents to fill the void with misinformation and outright lies about climate change,” he said. “By excising ‘climate change’ from his vocabulary, the president has surrendered the power that only he has to explain challenging issues and advance complex solutions for our country.”

With potentially dramatic fuel-use requirements coming to the car and truck worlds in particular, the issue has returned to prominence — however it may be defined.

Just last week, officials from the Environmental Protection Agency and the National Highway Traffic Safety Administration told U.S automakers that the administration is considering requiring cars and light trucks to average 56.2 miles per gallon by 2025. But automakers and conservative politicians are facing off against environmentalists over what mileage passenger vehicles can achieve.

Many of those carmakers, along with their congressional and gubernatorial allies, have cautioned that the administration could be pushing too aggressively for stricter fuel standards. On Wednesday, 14 GOP governors and one Democratic governor wrote top Obama officials to tell them that they need to take several factors into consideration when setting emission limits, including Americans’ need for large cars and trucks that can accommodate a variety of cargo, including skis, farm equipment and children’s car seats.

“If fuel economy standards increase too quickly, resulting in more expensive vehicles, consumers can be expected to hold on to their older vehicles longer and defer buying a new car, which could put auto jobs across the country at risk and delay compliance with federal air standards,” the governors wrote.

A host of states and industry groups are also challenging in federal court the EPA’s authority to regulate vehicles’ greenhouse-gas emissions.

National Automobile Dealers Association spokesman Bailey Wood asserted that the Obama administration is “trying to use regulatory fiat to get done what they couldn’t get done legislatively.” The White House was unable to get a bill setting federal limits on greenhouse-gas emissions through Congress in 2010.

Administration officials acknowledge that the measure has climate benefits but say they are also focused on cutting other pollutants, as well as reducing oil use and consumers’ fuel costs. “I think that’s the prize for all of us, and we think that’s within our reach,” said Gina McCarthy, assistant administrator for the EPA’s Office of Air and Radiation.

Ex-congressman Sherwood L. Boehlert (R-N.Y.), who led a group of former GOP politicians in calling last week for stricter fuel-efficiency standards, supports the administration’s efforts in that arena. “Talk of global warming doesn’t resonate with voters the way that the price of driving to work does,” he said.

“All of us who are involved in this issue have to talk about it in ways that are relevant to the American family,” Boehlert said in an interview. “We have to talk about it in the way they talk about it at the kitchen table.”

Many environmentalists echo that theme, promoting the new rules as having much more to do with reducing oil use than addressing climate change. Dan Becker, who directs the Center for Auto Safety’s Safe Climate Campaign, said that if the public debate ends up focusing on oil consumption, “we win,” because it is a more popular message than anything related to global warming.

Obama highlighted the fuel economy standards in a speech Tuesday at an aluminum plant in Iowa, as he has done before.

But instead of mentioning climate change directly, he described how he and others told U.S. automakers that in exchange for government aid, “they’d have to make some changes to compete, so we brought people together and set the first new fuel-mileage standards in more than 30 years. And that means fewer trips to the pump and less harmful pollution.”

Although the George W. Bush administration had sought to block regulation of vehicles’ greenhouse-gas emissions — which California and more than a dozen states had pushed to do — Obama embraced it. In May 2009, he brokered a deal between automakers, California officials, environmentalists and unions that incorporated California’s standards into a national program, an agreement that all sides hailed as breaking a decades-long stalemate over fuel efficiency.

That deal set greenhouse-gas emission limits for vehicles in the 2012 through 2016 model years. Now, officials are working on the rules for later models — and those are more ambitious.

By 2030, the current standards are slated to cut the nation’s annual greenhouse-gas emissions by the equivalent of 307 million metric tons of carbon dioxide and cut oil consumption by 1.8 million barrels a day. But the second round of rules, which will apply to cars and light trucks for model years 2017 through 2025, are proving more contentious because the emission cuts could more than double, and some domestic automakers question whether they can build much more efficient cars at a price consumers are willing to pay.

Truckers and their suppliers, however, have largely embraced greenhouse-gas limits as a way to cut their future fuel costs. This month, the government will finalize the first-ever greenhouse-gas rules for medium and heavy-duty trucks between the 2014 and 2018 model years. Depending on the final standards, by 2030 the truck and passenger vehicle rules combined could cut annual emissions by 725 million metric tons, or 13 percent of the nation’s current net emissions.

One of the wild cards in the current negotiations is whether the California Air Resources Board — which imposed the nation’s first-ever limits on vehicles’ greenhouse-gas emissions — will endorse a second national standard or opt to pursue stricter limits on its own.

“If we are not on a pathway to solving the global problem of climate change with the national program, we reserve the right to set our own standards,” said Tom Cackette, CARB’s deputy chief executive, who did not specify what those standards might be.

While domestic auto manufacturers have privately pushed for a much lower efficiency target than 56.2 mpg, at least one — General Motors — has indicated it could meet strict standards.

“We’re willing to be pushed by a tough national standard,” Greg Martin, GM’s Washington spokesman, said in an interview. But he added: “The devil is in the details.”

Car companies suggest the average cost of a vehicle would increase by as much as $6,000 if it had to average 56.2 mpg 14 years from now; federal agencies put that increase at $2,375.

Environmentalists such as Roland Hwang, transportation program director for the Natural Resources Defense Council, note that consumers would save an average of $6,412 in fuel costs over the vehicle’s lifetime. Hwang said NRDC and other groups are still pushing for at least 60 mpg as the 2025 standard, adding: “We are very concerned about loopholes that can substantially undermine the 56.2-mpg target benefits.”

Meanwhile, in a brief filed by Texas and other states in the U.S. Court of Appeals for the District of Columbia Circuit, the plaintiffs questioned the EPA conclusion that vehicle emissions “contribute to the perceived but undefined danger variously referred to as ‘climate change’ or ‘global warming.’ ” They questioned whether the greenhouse gases coming from tailpipes qualify as air pollutants.