The limits could nearly eliminate emissions from fossil-fuel burning plants after the most stringent standards go fully into effect, the people said. Another source familiar with the proposal said that there will be significant cuts to emissions from these plants, but potentially not as dramatic or extreme as others have suggested.

Although its greenhouse-gas emissions have been declining, the electric-power sector remains the country’s second-largest contributor to climate change, being responsible for a quarter of such emissions nationwide in 2021, according to EPA data. That has long made power plants a top target for climate regulations, and President Biden has previously promised to eliminate their emissions by 2035.

The Supreme Court has loomed over the effort. It ruled last year that the EPA during the Obama administration had exceeded its authority by building the first attempt at such regulations around a new system to push power companies to switch fuels across their fleets, and replace coal with cleaner options. The updated rules that Biden has promised have been held up for months in part because the agency has been trying to craft them in accordance with that decision so they might survive a conservative-majority court….

“EPA cannot comment because the proposals are currently under interagency review,” agency spokeswoman Maria Michalos said in an emailed statement. “But we have been clear from the start that we will use all of our legally-upheld tools, grounded in decades-old bipartisan laws, to address dangerous air pollution and protect the air our children breathe today and for generations to come.”

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The agency has been issuing a raft of new rule proposals just in recent weeks as it attempts to fulfill Biden’s big climate promises before he faces reelection. The administration spent most of its first year pushing its climate agenda through legislation, and now that Congress approved nearly $370 billion in new climate spending, Biden officials are trying to finish accompanying regulations before Republicans have a chance to take power and undo them.

Researchers who model emissions say that this collection of regulations is essential for meeting Biden’s commitment to cut total U.S. emissions in half from 2005 levels by 2030. Last year’s climate spending bill, called the Inflation Reduction Act, would get the country on course to reduce emissions by up to 42 percent by that target date. The executive actions on power plants, vehicles and methane would take it most of the rest of the way, another 6 percentage points of reduction, according to analysis released last month by the Rhodium Group.

“This is a step in the right direction, but it needs to be much more stringent,” Mejia said. “This proposal should be in line with the scale of ambitions that were promised to us.”

To help them reduce their emissions, Congress has provided subsidies to develop carbon-capture technology and make it more profitable. A federal tax credit provides as much as $180 per metric ton for businesses that use it. The Inflation Reduction Act also boosts by 70 percent the tax credit for the troubled legacy carbon capture technologies oil and gas companies have traditionally used to get more oil out of the ground, increasing it to $60 per ton.

Changes like those factor into EPA rulemaking. If the technology needed to comply is cheaper and more efficient, the agency can use that in its rulemaking to raise standards on the basis that it should be easier for businesses to meet them.

The agency is also factoring in flexibilities for plants, according to two people familiar with the details. Targets will vary at each plant based on size and use, and some coal-fired plants scheduled to retire in the coming years may not have to meet the new standards at all, the people said.