BILLINGS, Mont. - The federal government has approved strict new water quality standards sought by Montana over fears that coal-bed methane drilling in neighboring Wyoming could pollute interstate rivers.

Montana officials said Monday that the new rules would protect farmers from poor-quality water produced during exploration for coal-bed methane. Over the last decade, that industry has boomed just over the state line in Wyoming.

"It's a good thing to protect the water for our state," Montana Department of Environmental Quality Director Richard Opper said of the new rules. They were approved by the Environmental Protection Agency in a letter dated Friday.

But with a federal lawsuit over the issue still pending before District Judge Clarence Brimmer in Cheyenne, it was not immediately clear how far Montana could go in enforcing the standards.

The energy industry and state of Wyoming joined forces to oppose the rules in court after they were adopted by Montana's Board of Environmental Quality in 2006. They argued Montana's actions threaten to dampen energy development in the Powder River Basin, which straddles the border of the two states.

A spokeswoman for Wyoming Gov. David Freudenthal declined to comment Monday, citing the pending litigation.

The EPA said in its approval letter that the rules were "consistent with the requirements of the Clean Water Act."

More than 20,000 coal-bed methane wells have been drilled in northern Wyoming over the past decade.

Billions of gallons of water from underground aquifers are discharged during methane production. The discharged water is typically high in sodium and other salts, which can ruin crops and soils and harm fisheries.

If high salt levels are detected in rivers flowing into Montana, the state hopes to use its water quality rules to block additional methane development in Wyoming. That would require cooperation from Wyoming agencies that regulate the energy industry.

Opper said he hoped Wyoming could be persuaded to cooperate.

Negotiations between the two states over the issue collapsed in January before an agreement could be reached.

Montana Gov. Brian Schweitzer rejected a tentative deal that would have included the Tongue River in the new rules but largely excluded the Powder River and two of the Tongue's tributaries. Those water bodies are included in the new rules, according to the EPA letter.

Bruce Hinchey, president of the Petroleum Association of Wyoming, said the federal lawsuit objecting to the rules would probably continue. He said he did not know to what extent the EPA approval would take precedence.

Hinchey said the threshold for water pollution under Montana's standards was "ridiculously low."

"When they're setting levels that low, the impacts to the industry could be substantial," he said.

The EPA's action was welcomed by the Northern Plains Resource Council, a conservation group that prompted Montana to pursue the new rules two years ago, when state officials were reluctant.

Mark Fix, a Tongue River rancher and member of the group, said it was a "victory for farmers, ranchers and Montana citizens who depend on Montana's good-quality water."