LAS VEGAS - Interior Secretary Dirk Kempthorne and officials from seven Western states including Wyoming signed a sweeping agreement Thursday to conserve and share scare Colorado River water, ending a divisive battle among the thirsty rivals.

"This is the most important agreement among the seven basin states since the original 1922 compact," Kempthorne said, referring to a water-use agreement that also covers California, Arizona, Nevada, Utah, Colorado and New Mexico.

The 20-year plan, which took effect with Kempthorne's signature, resolved several legal disputes among water agencies in the states and formalized rules to cooperate during the ongoing drought gripping the region.

The states also commit, Kempthorne said, "to address future controversies on the river through consultation and negotiation before … litigation."

In a brief telephone interview from Las Vegas Thursday afternoon, Wyoming State Engineer Patrick Tyrrell said the agreement is a good deal for Wyoming.

"It preserves all our rights under existing law," Tyrrell said.

For the first time the states have an agreement that focuses on the management of the Lake Powell and Lake Mead reservoirs to deal with shortages in the Colorado River. The reservoirs will be allowed carry water over for use in the next year. The reservoirs have been operating under a "use it or lose it" principle, Tyrrell said.

The states now will know how the lower-basin states will share in shortages of water. Tyrrell said the river has been at only 50 to 60 percent of average capacity for several years.

The drought is largely responsible for the agreement, along with growth in the Colorado River lower basin, he said.

Climate change, Tyrrell added, "provides an uncomfortable backdrop for the agreement."

"We all hope the drought will end soon," he said.

Kempthorne also noted climate change as a factor. Saying he was "determined not to get ensnared in the politics of the issue," he called it "a simple fact that the Earth is warming."

"We have to figure out how this is going to affect our water supply," he said.

Kempthorne recalled a recent trip to the parched Southeast and quoted a 2003 report by the Council of State Governments that cites the prevalence of water conflicts "within states, among states, between states and the federal government, and among environmentalists and state and federal agencies."

"Everybody is talking about drought," he said before waving the signed documents aloft amid applause and calling the agreement a model for others to follow.

"If the seven states of the Colorado River basin can get together and work out a deal, then surely anybody can," he said, to laughter from an audience familiar with decades of sometimes acrimonious water fights.

"Celebrate this day," he said. "This is huge."