NEW YORK — President Barack Obama will impose even steeper cuts on greenhouse gas emissions from U.S. power plants than previously expected, senior administration officials said Sunday, in what the president called the most significant step the U.S. has ever taken to fight global warming.

A year after proposing unprecedented carbon dioxide limits, Obama was poised to finalize the rule at a White House event on Monday. In a video posted to Facebook, Obama said the limits were backed up by decades of data showing that without tough action, the world will face more extreme weather and escalating health problems like asthma.

“Climate change is not a problem for another generation,” Obama said. “Not anymore.”

Opponents vowed to sue immediately, and planned to ask the courts to put the rule on hold while legal challenges play out. Many states have threatened not to comply.

In his initial proposal, Obama had mandated a 30 percent nationwide cut in carbon dioxide emissions by 2030, compared to 2005 levels. The final version will require a 32 percent cut instead, said the officials, who weren’t authorized to comment by name and requested anonymity.

Environmental groups cheered the toughened rule, calling it a historic move that proves the global effort against climate change is beginning in earnest. Democratic presidential candidate Hillary Rodham Clinton vowed to defend Obama’s plan if she’s elected to replace him, and sought to use her support for the plan to draw a contrast with her GOP competitors.

“It will need defending. Because Republican doubters and defeatists – including every Republican candidate for president – won’t offer any credible solution,” Clinton said. “The truth is, they don’t want one.”

The final rule also gives states an additional two years – until 2022 – to comply, officials said, yielding to complaints that the original deadline was too soon. States will also have until 2018 instead of 2017 to submit their plans for how they’ll meet their targets.

But the administration will attempt to encourage states to take action earlier by offering credits those that boost renewable sources like wind and solar in 2020 and 2021, officials said.

The focus on renewables marks a significant shift from the earlier version that sought to accelerate the ongoing transition from coal-fired power to natural gas plants, which emit far less carbon dioxide. The revised rule aims to keep the share of natural gas in the nation’s power mix at current levels.

The stricter limits in the final plan were certain to incense energy industry advocates who had already balked at the more lenient limits in the proposed plan. But the Obama administration said its tweaks would cut energy costs and address concerns about power grid reliability.

The Obama administration previously predicted the emissions limits will cost up to $8.8 billion annually by 2030, although it said those costs would be far outweighed by health savings from fewer asthma attacks and other benefits. The actual price won’t be clear until states decide how they’ll reach their targets.

America’s largest source of greenhouse gases, power plants account for roughly one-third of all U.S. emissions of carbon dioxide and other heat-trapping gases blamed for global warming. Obama’s rule assigns customized targets to each state, then leaves it up to the state to determine how to meet them.

In the works for years, the power plant rule forms the cornerstone of Obama’s plan to curb U.S. emissions and keep global temperatures from climbing, and its success is pivotal to the legacy Obama hopes to leave on climate change. Never before has the U.S. sought to restrict carbon dioxide from existing power plants.

By clamping down on power plant emissions, Obama is also working to increase his leverage and credibility with other nations whose commitments he’s seeking for a global climate treaty to be finalized later this year in Paris. As its contribution to that treaty, the U.S. has pledged to cut overall emissions 26 percent to 28 percent by 2025, compared to 2005.

Even before the rule was finalized, more than a dozen states announced plans to fight it, setting up a near-certain confrontation with the Environmental Protection Agency, which by law can force its own plan on states that refuse to comply. Yet even in many of those states, power companies and local utility authorities have started planning to meet the targets in anticipation of being eventually forced to comply. Lawmakers in Congress were also expected to redouble efforts to use legislation to stop Obama’s regulation.

Yet the more serious threat to Obama’s rule will likely come in the courts. The Electric Reliability Coordinating Council, which represents energy companies, said 20 to 30 states were poised to join with industry in suing over the rule. The Obama administration has a mixed track record in fending off legal challenges to its climate rules.