Whatever happens in November, California's Proposition 8 will be an important landmark. Not only does California have 37 million residents, it also has a legendary trend-setting role. And California's increasing diversity raises the odds that a majority of its voters would support gay marriage in 2008.

Thus, Proposition 8 has exploded into the most expensive, extensive gay-marriage battle ever. The forces pushing it include all the Mormons who've made individual campaign donations totaling more than $9 million (more than 40 percent of the war chest, the Mormons for Proposition 8 group reported in mid-October). Conservative Catholics, including the Knights of Columbus, have kicked in more than $1 million. Other notable backers include Dobson's Focus on the Family (about $500,000), a wealthy board member of that group ($450,000), an Orthodox Jewish group based in New York City, evangelical groups from all over, miscellaneous Baptists and Muslims and Sikhs, the National Organization for Marriage (about $950,000), the American Family Association ($500,000), a couple of right-wing foundations ($1.5 million), and countless Republicans who don't necessarily belong to any of the other groups.

The forces against Proposition 8 include local governments, such as the Palm Springs City Council. Episcopal bishops oppose it, preaching tolerance, as does a lone Catholic priest in the Fresno area, who recently told his congregation that he's gay. Many businesses oppose Proposition 8, including the giant utility, Pacific Gas & Electric ($250,000 to the campaign against Proposition 8), AT&T ($25,000), and the Levi Strauss jeans company ($25,000 from the company and $100,000 from the company's chairman emeritus and his wife). The Valley Industry and Commerce Association in the Los Angeles area opposes 8. Google, based in California's Silicon Valley, normally stays out of politics, but Sergey Brin, the company's co-founder and president, offers this statement: "While we respect the strongly held beliefs that people have on both sides of this argument, we see this fundamentally as an issue of equality. We should not eliminate anyone's fundamental rights, whatever their sexuality, to marry the person they love."

Actor Brad Pitt ($100,000) and director Steven Spielberg ($100,000), many unions, Unitarians, miscellaneous rabbis and Presbyterians, psychiatrists' and psychologists' groups, the Gray Panthers and the American Civil Liberties Union ($1.5 million) oppose Proposition 8. So does the Human Rights Campaign ($2 million), the National Center for Lesbian Rights ($500,000), the Chinese Rainbow Association, the National Gay & Lesbian Task Force ($200,000-plus) and Tim Gill, the Denver-based founder of the Quark software company ($350,000). Democratic New York Gov. David Paterson has come out against it, as has Republican California Gov. Arnold Schwarzenegger. Democratic California Sen. Dianne Feinstein tells a gay magazine: "The views of Californians on this issue have changed over time ... I believe we should uphold the ability of our friends, neighbors, and co-workers who are gay and lesbian to enter into the contract of marriage." The Log Cabin Republicans, a gay group, runs Republicans Against 8, which pays for TV ads against the proposition.

Californians passed their initial gay-marriage ban by a wide margin (61 percent to 39 percent). The margin on Proposition 8 is closer and less certain. Polling up to late September indicated a slim majority had emerged in support of gay marriage. Then the first statewide TV ads from the other side aired -- claiming gay marriage is being forced on churches and public school curriculums -- and the polling suddenly tipped the other way. With a total of $27 million donated to the Proposition 8 campaign, and $19 million against it, it'll likely be a photo finish.

Many straight people -- regardless of their religion or lack of it -- have become more accepting of gay marriage. "They know a lot more about gay people. Maybe they know someone who is gay, which makes a huge difference. They know gay people are just people," says Bruce Bastian, who grew up Mormon in Idaho and then moved to Utah. Eventually, he came out as a gay and gave up the Mormon Church. He got rich by founding the WordPerfect software company, and he's donated more than $1 million to the campaign against Proposition 8.