BOULDER CITY, Nev. — Interior Secretary Gale Norton signed a deal Thursday meant to end years of bickering among California and six other states that rely on Colorado River water. The deal ensures more water for fast-growing cities in Southern California while limiting supplies to farms.

More than 30 million acre-feet of water — enough to cover the state of Pennsylvania a foot deep — will move from farms to cities in Southern California over the 75-year life of the deal. Beyond serving burgeoning urban populations, the shift is designed to curb California's overreliance on the river.

"Today we celebrate an historic event on the Colorado River, the river that brings life to this arid region of our nation," Norton said. "With this agreement, conflict on the river is stilled."

Much of the water affected by the deal will go to San Diego. The Imperial Valley, California's biggest user of Colorado River water, will sell as much as 90 billion gallons each year to San Diego — roughly one-third of the city's future water needs.

Cities like San Diego and Los Angeles had been taking billions of extra gallons of Colorado River water over the years, something other Western states that rely on the water have bitterly contested.

President Bush said in a statement that the deal "improves the lives of citizens in the Western United States."

In an interview, Norton described the agreement as "monumental" and said it is a roadmap for future water trades in the West, which will face increasing demand for scarce resources in years to come.

"This puts in place the basic building block of future agreements to meet water needs," Norton said Wednesday.

The government's approval also restores California's privileges to draw additional water from the river for 15 years. The Interior Department revoked those privileges when California missed a Dec. 31 deadline to reach an agreement.

Nevada, which was linked to the California deal, also lost 10 percent of its supply. With the new accord approved, Nevada will be allowed to draw water for fast-growing Las Vegas.

Four Southern California water agencies, who have spent years squabbling over the deal, signed the deal last week with little fanfare. Norton's signature was the final authorization needed to implement the agreement.

Top officials from the four agencies attended the signing ceremony, along with Gov. Gray Davis, whose aides led a concerted effort to resolve a series of disagreements that nearly derailed the deal.

California made its vow to curtail its use of the Colorado River during the Great Depression, when the Hoover Dam was built. Over the years, however, the state has come to rely on excess water from the river as a major supply source for Southern California.

"We're following through with the promises that were made 70 years ago," Norton said. "Had we not resolved it now it could have been a serious obstacle to meeting the water needs throughout the Colorado River system for the long-term future."