WASHINGTON — The Environmental Protection Agency plans to unveil new regulations Monday to reduce smog from automobiles, including cutting by two-thirds the level of sulfur in gasoline, people familiar with the agency’s deliberations said.

The EPA is expected to stick to the broad targets included in a proposed rule published last year that would lower sulfur in gasoline to 10 parts per million from the current 30 parts, the three people said. New limits will also be imposed on tailpipe emissions.

“This is the most significant move to protect public health that the EPA will make this year,” said Frank O’Donnell, president of Clean Air Watch, who said he hasn’t seen the final rules though he supported the proposal. “There is literally no more effective tool to fight smog. Every American will breathe easier because of these standards.”

Supporters of the rules say they could be one of President Obama’s most significant environmental initiatives. Smog has been linked to asthma, lung cancer and heart disease.

The new regulations were the subject of years of conflict between automakers, which support cleaner fuels that lower their costs, and the oil industry, which will bear billions of dollars in extra costs.

EPA spokeswoman Alisha Johnson declined to comment on the final rule. “We’re continuing to work to finalize the rule and will announce it once it’s ready,” she said.

Automakers have supported the so-called Tier 3 motor vehicle and fuel standards because the new U.S. rules would generally match California’s. That means the industry could produce one set of cars for the U.S., rather than two, lowering costs.

Sulfur occurs naturally in crude oil and can build up on a vehicle’s catalytic converter, making a device that is designed to reduce smog-forming pollutants less effective over time, said Clean Air Watch’s O’Donnell.

“If the catalytic converters aren’t working right, breathers suffer,” he said.

With higher sulfur levels in gasoline, automotive engineers must calibrate vehicles to burn off the pollutant, said Wade Newton, a spokesman for the Alliance of Automobile Manufacturers, which represents 12 companies including General Motors and Volkswagen. That process consumes extra energy and worsens fuel economy, he said.

“Our clean autos need clean fuels to run on,” Newton said. “They really need to go hand in hand. A lower sulfur level is also important because without it, it becomes more expensive for drivers.”

The oil industry will have to pay an estimated $10 billion in capital costs and $2.4 billion in annual compliance costs, American Petroleum Institute President and Chief Executive Officer Jack Gerard wrote on Wednesday in a letter to supporters about the pending announcement. The Washington-based trade group has projected the regulations could increase gasoline prices by up to 9 cents a gallon.

Regulators haven’t provided enough evidence that the lower sulfur levels will “appreciably improve air quality,” Gerard wrote. The EPA is moving “too far, too fast,” he said, “to impose restrictions that are both costly and unnecessary.”

Companies such as Exxon Mobil and BP opposed the rules, saying in written comments to EPA that the deadline for compliance was too short and the agency hadn’t shown significant health benefits from lower sulfur limits.