CALIFORNIA reapportionment appears headed for state Supreme Court.By nearly every account, no viable alternative exists after Monday's veto by Republican Gov. Pete Wilson of three Democratic-backed plans to redivide state Senate, Assembly, and US congressional districts. The Legislature immediately tried to override the veto, but didn't have the votes. It needed a two-thirds vote of both houses, or 54 Assembly and 27 state Senate votes. The override attempt failed in the Assembly 41 to 32 and in the Senate 22 to 10. The plans had been approved last week by the state Legislature on strictly partisan votes. Mr. Wilson and GOP backers wanted plans that would create districts where they had a chance to win, based on the rise in Republican registrants. Democrats say their plans reflected such rise but also have to comply with the federal Voting Rights Act guaranteeing minority representation. But Governor Wilson says the plan violates the Voting Rights Act, by dividing up compact minority districts so that minorities would have less of a chance at getting elected. The Legislature could come up with new plans it hopes the governor will not veto, or that have a better chance of overriding. Most likely, the state Supreme Court will step in, hire a so-called "court master," who then hires a technical staff which considers current and new submissions. A previously appointed gubernatorial task force, the NAACP and the Mexican-American Legal Defense and Educational Fund (MALDEF) are among those poised with alternative plans to submit. "What is clear is the issue is in no way settled," says Sherry Jeffe, a political scientist at Claremont College. In 1971 and 1981, the court imposed temporary congressional districts to comply with federal law. According to Dan Schnur, spokesman for Governor Wilson, the new plan must be approved by the federal Justice Department by Jan. 1, in time for 1992 elections. Until then, there is no way to gauge whether California's net gain of seven seats will favor Republicans or Democrats. A new, Latino district in Los Angeles - written into each of the three vetoed plans - is up in the air as well. With suits pending against the US Census Bureau - alleging an undercount of minorities and cities - the seven sites could be expanded to eight. "The only thing that is sure is that this process affects 12 percent of the US Congress - it's such a large delegation it really impacts the direction of national policy," says Jeffe. Democrats now control 26 of California's 45 seats in Congress, 47 of the state's 80 Assembly seats, and 26 of the 40 state Senate seats. Though Republicans want to draw even with the Democrats in all three bodies, severe divisions between moderates and conservatives have complicated rather than assuaged the current mess. "In the past, Republicans have stuck together," says Tony Quinn, a political analyst. "Now the fight threatens how many [Republicans] there'll be and what kind [moderate, conservative]." Meanwhile, the process continues to dominate the state agenda. "It's been impossible to do anything else," says Jeffe. "No health-care insurance reform, workmen's comp, auto insurance reform.... Governor and legislative staffs have excluded everything else."