California officials have been working for months on a plan to “Trump proof” the state’s leading edge environmental and climate policies, in the event that former President Donald J. Trump returns to the White House and follows through on his promise to gut them.

Whether California succeeds could affect more than a dozen other states that follow its emissions rules, and could have global impact because the state’s market muscle compels auto makers and other companies to conform to California standards.

The strategy now being crafted in Sacramento includes lawsuits designed to reach wide-ranging settlements with industries that generate greenhouse gases, and new rules and laws that rely on state authority and would be beyond the reach of the administration.

Mr. Trump, who considers climate change a “hoax,” has promised to weaken every major federal climate regulation, as he did in his first term.

But he is also expected to try to blow up California’s climate policies, which have set the pace for the rest of the nation and the world. The state is requiring about three-quarters of new trucks sold there after 2035 to be zero emissions. And in a request that is pending, California wants permission from the Biden administration to enact one of the most ambitious climate rules of any nation: a ban on the sale of new gas-powered passenger vehicles in the state after 2035.

Both rules are far tougher than federal policy and could have influence beyond the United States, given California’s standing as the world’s fifth-largest economy. China and the European Union have already adopted parts of California’s car and truck tailpipe emissions reduction programs.

The Democratic-controlled state legislature has also passed a first-in-the-nation law requiring major companies to disclose their greenhouse emissions. And it has strengthened the authority of local governments to shut down oil and gas projects in their communities. Next month, Californians will be asked to approve a ballot measure to create a $10 billion “climate bond” to pay for climate and environmental projects.

Under a provision of the 1970 Clean Air Act, the Environmental Protection Agency has for decades given California a waiver that allows it to enact pollution controls that are stricter than federal regulations. Federal law also allows other states under certain circumstances to adopt California’s standards as their own.

Sixteen states have pledged to follow the California car rule and 10 states have adopted the truck rule, meaning that the California regulations would apply to about 40 percent the United States auto market.

Mr. Trump has promised to revoke the waiver. “California has imposed the most ridiculous car regulations anywhere in the world, with mandates to move to all electric cars,” Mr. Trump has said. “I will terminate that.”

At the same time, the legality of the waiver is being challenged by 17 Republican attorneys general and several oil groups in a lawsuit that may head to the United States Supreme Court.

On the campaign trail, Mr. Trump has continued his long-running feud with California’s Democratic governor, Gavin Newsom. Mr. Trump has called him an “environmental maniac” who is “crushing our great automakers in Michigan, Wisconsin, Georgia, North Carolina and South Carolina, crushing them under his leadership.”

A spokeswoman for the Trump campaign, Karoline Leavitt, declined to comment on California’s plans.

Mr. Newsom, who is seen as having White House ambitions of his own, has made clear that he intends to forge ahead on environmental regulation regardless of whether Mr. Trump returns to the presidency.

“California has long led the nation in pioneering climate policies and innovation,” said Mr. Newsom in a statement. “Those efforts will continue for years to come. That includes partnerships with private companies, such as automakers, and agreements with other countries — everywhere from China to Norway to Canada — to combat the climate crisis together.”

Other top Democrats in the state, including Attorney General Rob Bonta, are working with the state’s climate regulator, the California Air Resources Board, on the “Trump-proofing” strategy. Assembly Speaker Robert Rivas said the state legislature will be ready to meet in a special session after the November election if necessary.

When Mr. Trump became president in 2017, California officials were caught flat-footed, said Mary Nichols, who was the state’s top climate regulator from 2007 to 2020 and now informally advises state policymakers. “It came as a shock,” she said.

As the Trump administration dismantled Obama-era environmental rules and then took aim at California’s policies, the state fought back, Ms. Nichols said. California filed more than 70 climate and environmental lawsuits against the Trump administration, prevailing in more than half of them.

That kind of record is not assured in the future, in part because Mr. Trump reshaped the nation’s courts, appointing more than 200 federal judges. Those appointments include three Supreme Court justices, who helped form a conservative supermajority that delivered decisions to restrict the government’s authority to regulate climate, air and water pollution. As soon as January, the court could hear the case that is challenging California’s waiver under the Clean Air Act.

State officials and lawmakers are working to try to protect California’s policies even if it loses its waiver.

They plan to build upon their most successful legal gambit during Mr. Trump’s first term. In 2019, the Trump administration revoked California’s waiver — the first time the federal government had done so since the Clean Air Act was passed in 1970. The Biden administration would later restore it, but the lapse had limited impact because California had secretly struck legal agreements with four of the world’s largest automakers — Ford, Volkswagen, Honda and BMW — to reduce their tailpipe emissions according to limits set by the state.

The move blindsided and enraged Mr. Trump, and his administration in turn threatened to withhold federal highway funds from California, unsuccessfully sued the state for partnering with Quebec on its emissions reduction program, and opened an antitrust investigation into the automakers that signed on to the deal.

But the deal with automakers, which expires in 2026, endured and grew: Volvo and Stellantis have since signed on. California regulators are now talking to the companies about even stricter emissions limits, and expanding the agreement to include other automakers and possibly other states.

“We are going to fight back hard,” said Phil Weiser, the Democratic attorney general of Colorado. “We are going to coordinate.”

Ms. Nichols, the architect of the automaker deal, also said that “back channel” conversations are happening about ways to forge legal agreements to reduce emissions from other industries, including electric utilities, oil companies and global corporations that have business in California.

The state is betting that companies would prefer to enter into a legal agreement that requires them to cut emissions or pay for environmental remediation rather than gamble on a court decision that could result in much higher sums. Many companies would also like to avoid the uncertainty of federal rules that change with each administration.

“When you have a settlement with private industry, it doesn’t matter if there is a change in administration,” said Paul Nolette, a professor of political science at Marquette University who is familiar with California’s strategy.

Mr. Nolette and others said the $206 billion settlement reached in 1998 between 46 states and tobacco companies offered lessons for how a climate deal between several states and industries could be structured.

The California attorney general’s office hopes to create a foundation for such deals following its lawsuit last year accusing five of the world’s largest oil companies of knowingly contributing to climate damage, and its lawsuit last month alleging that Exxon Mobil misled consumers into believing that many plastic products were recyclable when they were not.

The discovery documents and financial disclosures emerging from those complaints could lead to settlements under which companies might agree to emissions reductions, said Ms. Nichols and Mr. Nolette.

Legal settlements would likely be just one part of the state’s “Trump-proofing.”

“California has lots of other tools, including the power of the purse — particularly when it comes to procurement,” said Craig Segall, the former assistant chief counsel at the California Air Resources Board, who is now senior vice president at Evergreen Action, an environmental advocacy group.

For example, during the Trump administration, California banned the purchase of state vehicles made by companies that backed Mr. Trump’s efforts to roll back the state’s fuel-efficiency rules, including General Motors and Fiat Chrysler, which later became Stellantis. Eventually, those companies reversed course and sided with California.

Other leverage is under consideration, said Mr. Segall and others familiar with the planning.

State regulators could impose penalties on the use or purchase of vehicles that burn gasoline while California lawmakers could require that the resulting revenue be used to subsidize the purchase of electric vehicles.

Regulators could also limit emissions stemming from vehicles that are linked to enormous facilities like warehouses that are a hub for diesel trucks. A similar rule recently took effect in Los Angeles.

“Any state can have that,” said Mr. Segall. “It doesn’t need the federal waiver. These kinds of things are not popular, but in a world where there is destruction of the other climate tools, states can take these defensive measures.”

More than a decade ago, California launched a “climate diplomacy” relationship with China that endures. Delegations of Chinese officials have met multiple times with California Air Resources Board officials to share information and research. The meetings have borne fruit: China essentially cut-and-pasted portions of the California clean car rules — a policy move that helped drive China to the cutting edge of electric vehicle development.

California’s outreach to other countries will continue, state officials said. In addition to China, the state has influenced the European Union, which is mandating EV-only auto sales after 2035 and truck sales after 2040.

The state has served as co-chair of the International Carbon Action Partnership, an organization of economies that have established “cap-and-trade” programs, in which industrial polluters buy and sell emissions credits. Among those economies is Quebec, which has linked its carbon dioxide cap-and-trade market with California’s.

The Canadian province has used revenues of the program to help pay for incentives and chargers for electric vehicles, which now make up nearly 30 percent of new car sales in the region, compared with 8 percent in the U.S.

“Without the carbon market and the linkage with California, we wouldn’t be able to achieve this in Quebec,” said Benoit Charette, Quebec’s environment minister. “No matter the result of the federal election, California is our partner.”