WASHINGTON — Congressional Republicans are lining up against the possibility of the Environmental Protection Agency blocking what would be North America’s largest open pit mine in a region of Alaska that supports some of the richest wild salmon runs in the world.

The top investigator for the science committee in the House of Representatives, Georgia Republican Rep. Paul Broun, wrote the EPA this week and said its study of the proposed Pebble mine in the Bristol Bay region fell short and shouldn’t be used to block development. That follows the claims of California Republican Rep. Darrell Issa, the House oversight chairman, and Ohio Republican Rep. Jim Jordan that the EPA doesn’t have the authority to pre-emptively veto permits for the mine.

Supporters of Pebble and politicians in Alaska and Washington, D.C., say they’re worried that the EPA will use its study to shut down the possibility of the massive copper and gold mine even before mine officials submit plans for approval and permit applications. Opponents of the mine are urging the EPA to act. The hotly debated study, which the agency calls a draft assessment, found that even if such a mine operated smoothly up to 87 miles of rivers or streams would be lost or blocked, as could thousands of acres of wetlands that are vital fish habitat.

The EPA, while saying it has the authority to block the plans even before the developers apply for permits, says it’s made no decision to try to stop the mine.

Associate EPA Administrator Arvin Ganesan said congressional Republicans were fretting about a “hypothetical,” and the federal study isn’t a finished product.

He recently wrote members of Congress that the agency did the Bristol Bay study to understand the effects of large-scale mining on water quality and fishery resources. “We are conducting the assessment to inform future decision making,” Ganesan wrote.

A group of independent scientists who are reviewing the quality of the EPA’s study held meetings in Anchorage this week. At least some have suggested that the study needs more work; their recommendations are due in the fall.

The proposed Pebble mine is one of the most controversial development prospects in the history of Alaska. The Bristol Bay region produces about half the wild sockeye salmon worldwide, with an annual commercial harvest of 27.5 million over the past decade.

The Pebble prospect appears to be a unique case for the EPA. The agency, when asked repeatedly this week, provided no other examples in which it’s conducted a similar assessment of a mining prospect before the plans for the mine have been submitted.

The EPA did the study after being petitioned by tribal groups and Bristol Bay Native Corp., which says the risk is too great and wants the agency to stop the mine.

More than 200,000 people submitted written comments on the assessment and roughly 90 percent supported the agency’s findings, according to the EPA.

Pebble advocates argue that mining and fishing can coexist in the Bristol Bay area and that the project would bring badly needed jobs. The Pebble Partnership, the group behind the Pebble mine project, has called the deposit one of the largest of its kind in the world, with the potential of producing 80.6 billion pounds of copper, 107.4 million ounces of gold and 5.6 billion pounds of molybdenum – which is used to make stainless steel – over the next three decades.

Pebble and its supporters told the EPA that the study was rushed and flawed. The Pebble Partnership, which hasn’t yet submitted its development plan, said the EPA assessment was based on a hypothetical mine that won’t happen instead of its actual plans.

The EPA made it clear in a letter to Congress that it has the authority to veto Pebble mine discharges if it chooses to do so. EPA Administrator Lisa Jackson has the power under the Clean Water Act to veto discharges that she finds would have an “unacceptable adverse effect” on fisheries, including spawning areas, according to the agency. It said that could happen before a mine applied for the necessary dredging and filling permits from the Army Corps of Engineers.

Those are fighting words for Republicans in Congress, who’ve made the EPA a target on a range of issues.

Issa called the EPA’s argument an “unprecedented and legally questionable interpretation of the Clean Water Act.” Broun followed that up with his letter to the EPA.

“These are serious concerns. If EPA ultimately uses this watershed assessment as justification to pre-emptively veto mining permits in Bristol Bay – not withstanding EPA’s legal authority to do so – the scientific credibility of the assessment will need to be beyond reproach,” Broun wrote. “This is obviously not the case.”

Alaska’s congressional delegation – including its lone Democrat, Sen. Mark Begich – also is against the EPA moving quickly to stop the mine.

“I remain opposed to any pre-emptive decision on the Pebble mine. While the project needs to meet a high hurdle – protecting the world’s largest and most valuable salmon run – developers should be allowed to present their project and it should succeed or fail on its merits,” Begich said in a statement.