Gov. Arnold Schwarzenegger and many other moderates in California say a ballot proposition passed Tuesday that puts in place an unusual 'top two' primary election process could lead to a renaissance for centrist lawmakers. But it's almost certain to face a legal challenge _ and its impact remains an open question. Proposition 14, modeled on a similar law in Washington state, was approved by 8 percentage points. The measure will create a single, open primary in which the top two finishers, regardless of party, advance to the general election runoff, paving the way for Republican-vs.-Democrat, Democrat-vs.-Democrat or Republican- vs.-Republican contests. With nearly one in every eight U.S. House members coming from California, the proposition brings into increased national focus an experiment underway in Washington state since 2008. The campaign was spearheaded by Schwarzenegger and his moderate new lieutenant governor, Abel Maldonado, both Republicans. Maldonado, a former state senator, secured the ballot measure as part of an agreement to vote for the stalemated Democratic budget last year. Although two Republicans led the fight, their party isn't on board. 'Where this puts us is, we're going to disenfranchise 5.3 million Republican voters who should have a voice in who their nominee is,' state GOP spokesman Mark Standriff said. The Democratic Party is also opposed, with its resistance led by U.S. House Speaker Nancy Pelosi, D-Calif. She argued that the measure would distort the political process. California Secretary of State Debra Bowen, a Democrat who hasn't taken sides, has said lawyers are girding for a challenge. The system in Washington state, which was approved in 2004 and put in place before the 2008 election, is still being challenged in federal court. And California's experiment with a nonpartisan 'blanket' primary in the 1990s was struck down by the U.S. Supreme Court. (A 'blanket' primary is similar to 'top two,' except that the top vote-getters from each party advance.) Rick Hasen, a professor at Loyola Law School in Los Angeles and advocate of a 2004 'top two' proposition, said he expects this law to hold up, although it could be challenged on two counts _ because it hurts minor parties and independents and because it could lead to voter confusion. If it does survive a legal fight, some experts are asking whether the proposition will have its intended effect by adding moderate lawmakers. 'I would expect a small increase,' said Eric McGhee, a research fellow at the nonpartisan Public Policy Institute of California. 'There's just not much evidence that it adjusts the ideology of elected officials that much.' Bruce Cain, a political science professor at the University of California at Berkeley, said opponents of the 'top two' proposition were left with little choice but to let it pass given the anti-establishment political environment. 'They didn't think it was good time to try and defend the status quo,' Cain said. 'They think, through coordination this won't hurt them that much.' Independent Washington state pollster Stuart Elway said that his state has a relatively moderate government but that he wasn't sure whether it was the cause or a symptom of the state's historically unusual primary process. It had a 'blanket' primary for decades before adopting the 'top two.' 'We tend to think that because we had (a) blanket primary for 70 years and you could vote for either party in the primary that had a moderating influence,' Elway said, adding that 'top two' hasn't had much time to affect the state's politics. -0-< Staff writer Sandhya Somashekhar contributed to this report. 