Nov 2 (Reuters) - The Biden administration on Tuesday unveiled a plan to slash emissions of the greenhouse gas methane from oil and gas operations as part of its broader strategy to crack down on climate change, drawing cautious support from both environmental groups and drillers.

The announcement coincided with the United Nations climate conference in Glasgow, Scotland, where the United States, the world's second-largest greenhouse gas emitter, is seeking to reclaim leadership on the world stage by demonstrating tangible steps to curb emissions at home.

President Joe Biden has set a target to slash greenhouse gas emissions by more than 50% by 2030 but is struggling to pass major climate legislation through a deeply divided Congress, making policies by federal agencies more crucial.

His administration and the European Union are also seeking to lead a new international pact to reduce methane by 30% by 2030, drawing participation from some 90 countries.

At the center of the U.S. plan to tackle methane domestically is an Environmental Protection Agency proposal that will for the first time require oil and gas operators to aggressively find and repair methane leaks. Oil and gas operations account for a third of methane emissions.

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"The timing of this is critical. As we speak, world leaders are gathering right now in Glasgow and they are looking to the United States for true leadership," U.S. EPA Administrator Michael Regan told Reuters in an interview. "This proposal is absolutely bold, aggressive and comprehensive."

Specifically, the proposal will require companies to monitor 300,000 of their biggest well sites every three months, would ban the venting of methane produced as a byproduct of crude oil into the atmosphere, and require upgrades to equipment such as storage tanks, compressors, and pneumatic pumps.

The EPA rules would most likely take effect in 2023 and would be aimed at slashing methane from oil and gas operations by 74% from 2005 levels by 2035, an amount equivalent to the emissions created by all U.S. passenger cars and planes in 2019, according to the summary.

The American Petroleum Institute, which represents the U.S. oil and gas industry, said it was reviewing the proposals.

“We support the direct regulation of methane from new and existing sources and are committed to building on the progress we have achieved in reducing methane emissions," it said in a statement.

Major producer BP Plc, which has been seeking to burnish its green credentials and is investing heavily in clean energy, said it applauded the EPA proposals.

Washington-based environmental group Earthworks also called the proposals a positive step, but added that it would "continue to advocate for the strongest possible standards" as the EPA seeks feedback on the plan.

A crew works on plugging Federal 3-32X, an abandoned oil well confiscated by the state of North Dakota. The well, first drilled in 1978, is southwest of the town of Watford City, in the Little Missouri National Grasslands. The state devoted $66 million in CARES Act money to plug abandoned wells and reclaim polluted land. (Erika Bolstad/Pew Charitable Trusts/TNS)
A crew works on plugging Federal 3-32X, an abandoned oil well confiscated by the state of North Dakota. The well, first drilled in 1978, is southwest of the town of Watford City, in the Little Missouri National Grasslands. The state devoted $66 million in CARES Act money to plug abandoned wells and reclaim polluted land. (Erika Bolstad/Pew Charitable Trusts/TNS)

QUARTERLY MONITORING

Methane is the second-biggest cause of climate change after carbon dioxide. Its high heat-trapping potential and relatively short lifespan in the atmosphere means cutting its emissions can have an outsized impact on the trajectory of the world's climate.

The EPA's well monitoring proposal applies to sites emitting an estimated three tons of methane per year or more, a threshold the agency said would capture sites responsible for 86% of leaks. Smaller sites will require less scrutiny.

Oil and gas industry groups had pressed the EPA to exclude smaller wells from the regulations, citing the sheer number of such wells and the costs of the monitoring and repairs.

Environmental advocates, meanwhile, had pushed for all well sites to be covered, and were also seeking limits on flaring: the practice of burning off methane that comes out of the ground as a byproduct during crude oil drilling.

The administration's methane strategy will also include a new proposal by the Pipeline and Hazardous Materials Safety Administration requiring companies to monitor and repair leaks on about 400,000 miles of previously unregulated natural gas gathering lines.

The administration's plan also proposes new voluntary measures from the Agriculture and Interior departments to tackle methane emissions from other major sources, including landfills, agriculture and abandoned wells and coal mines.

The EPA said it will release a supplemental proposal next year to flesh out the rules and possibly expand them to include additional methane sources, including abandoned oil and gas wells, flares and tank truck loading.

(Reporting by Valerie Volcovici and Nichola Groom; Editing by Gerry Doyle, Steve Orlofsky and Jonathan Oatis)