Advocacy groups have ramped up pressure on the Obama administration in the past week as the Environmental Protection Agency prepares to finish a standard that would limit the amount of sulfur allowed in gasoline.

Environmental, public health groups, automakers and congressional Democrats have pushed the EPA to maintain the proposed limit of 10 parts per million of sulfur dioxide, down from 30 ppm, that would take effect in January 2017. It would clean up three-quarters of the remaining 1 percent of smog-forming emissions the current standard didn't eliminate.

"According to the National Association of Clean Air Agencies, the proposed standards would increase the cost of gasoline by about 1 cent per gallon and add $150 to the cost of a new car, meaning our air can be much cleaner without a high cost to consumers," a group of House Democrats wrote to EPA Administrator Gina McCarthy. "Those suffering most from air pollution cannot afford to wait any longer for relief."

The oil industry and Republican opponents of the standard, which is known as Tier 3 and could come as early as next week, are arguing for more time.

"That is far too short of a period of time," Patrick Kelly, senior policy adviser with the American Petroleum Institute, said of the deadline that is less than three years away. "In a rule of this magnitude, EPA has always allowed for up to four years of lead time."

The proposed standard is incremental compared with the previous iteration, Tier 2, that came in 1999. Those standards ratcheted down sulfur content from 300 ppm to their current level, which proponents say saved thousands of lives by reducing exposure to smog-forming pollutants linked to heart and respiratory ailments.

The EPA says the Tier 3 standard would prevent up to 2,400 premature deaths and provide between $8 billion and $23 billion in annual health benefits per year by 2030.

The new standard is coming at a time when President Obama is increasingly relying on executive action to curtail emissions that drive climate change and harm human health. Those efforts include new fuel-efficiency targets set Tuesday for heavy-duty trucks, as well as ones finalized in 2012 that would require light-duty vehicles to get 54.5 miles per gallon by 2025.

The oil and refining industries have conceded that blocking the sulfur standard is no longer an option. Instead, they are pushing the EPA in meetings this past week to draw out the deadline to 2020.

Some refineries would have to shut down operations outside of routine maintenance schedules to upgrade their facilities, choking gasoline supplies and raising prices in the process, said Brendan Williams, senior vice president of advocacy with the American Fuel and Petrochemical Manufacturers, which represents the nation's refineries.

Williams said maintenance shutdowns are scheduled on five-year timeframes, so the 2017 start date for the new standard would come too fast. He also said the EPA may be overestimating the effectiveness of the credit-trading scheme that the agency says will plug the gap for non-compliant refineries.

"We will have to make the adjustments during shutdowns and, given shutdown schedules, we won't be able to complete the work by 2017," said Williams, who met with the White House Office of Management and Budget on Wednesday.

But the standard's proponents argue sulfur's harm to human health justify shutdowns outside the routine maintenance cycle, no matter the cost. They also cite the benefits of avoided medical costs and increased productivity from fewer work and school absences.

"EPA has built in more than enough lead time and maximum flexibility for refineries to facilitate compliance. EPA must not delay the implementation, delay will cost human lives. These standards need to be finalized and implemented as soon as possible to protect public health," said Paul Billings, senior vice president of the American Lung Association.

Some groups that support the standard, including the Union of Concerned Scientists, the Sierra Club and the Environmental Defense Fund, met with the Office of Management and Budget last week to make that case.

Automakers are pushing the EPA to finalize the standard as well, as they're producing vehicles to run on gasoline with lower sulfur content.

Delaying implementation, they warn, would allow refineries to churn out gasoline that's incompatible with catalytic converters. In turn, that could damage or dismantle emissions control systems. They have rejected claims by the oil and refining industry that cars tooled to run on Tier 3 gasoline can handle current blends.

"Just like horses and carriages used to go together, today fuel and auto standards work in tandem. Clean cars need clean fuels," said Gloria Bergquist, a spokeswoman with the Alliance of Automobile Manufacturers, which represents a dozen major car companies.