BILLINGS, Mont. - Wyoming's attorney general asked the U.S. Supreme Court on Friday to dismiss a lawsuit alleging the state's agriculture and energy industries are using too much water in violation of an interstate agreement.

Montana sued its southern neighbor last year. It claimed farmers and other water users along the Powder and Tongue rivers were being harmed by Wyoming's excessive water use.

The dispute between the states stretches beyond this one issue. Scarce water resources coupled with extended drought have turned the states' shared waterways into a recurrent political battleground.

The Tongue and Powder rivers flow through arid regions of northern Wyoming and southern Montana before draining into the Yellowstone River. The Supreme Court case centers on the Yellowstone River Compact, a 1950 agreement that allocated each state a share of water from the Yellowstone and its tributaries.

In court documents filed Friday, Wyoming Attorney General Bruce Salzburg argued the lawsuit should be thrown out because it was "fundamentally flawed." The lawsuit addressed the use of water across the river basins - not just from the rivers themselves, which is what Wyoming claims the compact covers.

"We are not violating the compact," Salzburg said in a telephone interview Friday.

The states are also engaged in a separate federal lawsuit over new Montana water quality standards affecting the Tongue and Powder rivers, which Wyoming officials contend could dampen energy industry development.

To the west, the states have each been seeking a greater share of water from the Big Horn River, another Yellowstone tributary popular among anglers.

In the case of the Yellowstone compact, Montana asserts Wyoming is storing water in reservoirs that should be delivered downstream and also allowing excessive pumping of underground water reserves that feed into the two rivers.

Those groundwater reserves are tapped by some Wyoming farmers to irrigate their fields. In addition, energy companies remove billions of gallons of groundwater during production of coal-bed methane, a type of natural gas prevalent in the border region.

Salzburg said his state's construction of reservoirs had been encouraged by the compact, and he suggested Montana do the same if it wants to guard against dry periods.

He also said the depletion of groundwater by energy and agricultural interests was largely outside the scope of the 1950 agreement.

"Pumping water from deep aquifers isn't within the contemplation of the compact," he said. "It simply doesn't address those things."

A spokeswoman for Montana Attorney General Mike McGrath declined immediate comment Friday, saying the office had just received Wyoming's 168-page court brief.

"We're still reviewing it," spokeswoman Lynn Solomon said.

In 2004 and again in 2006, Montana had called on Wyoming to increase flows in the Tongue and Powder rivers to satisfy Montana irrigators. Both requests were denied by Wyoming.

When Montana sued in January 2007, McGrath said Wyoming was giving preference to its own residents and businesses at the expense of downstream farmers in Montana.

North Dakota, also a member of the Yellowstone compact, was named as a second defendant in the lawsuit. But Montana officials have said its inclusion was a formality and that they have no disagreement with their eastern neighbor.

Montana has 30 days to file its response to Wyoming's move to dismiss the case.