California is asking the federal government to pay 75 percent of the hundreds of millions of dollars in repairs to the badly damaged spillways at the nation’s tallest dam, a state water agency spokeswoman said Monday. The question of whether taxpayers or the water contractors that get water via the Oroville Dam would foot the biggest share of the bill has been one of many contentious ones in the aftermath of this winter’s damage at the dam, which is an anchor of the state’s water supply system.