Some of the nation’s most divisive social issues — gay marriage, abortion and affirmative action — went before voters Tuesday as 36 states passed judgment on ballot measures as well as candidates.

Of the 153 measures at stake, the most momentous was a proposed constitutional amendment in California that would limit marriage to heterosexual couples.

Similar measures have prevailed previously in 27 states, but none were in California’s situation — with thousands of gay couples already married in the aftermath of a state Supreme Court ruling in May.

The opposing sides together raised about $70 million, much of it from out of state, to wage their campaigns. The outcome, either way, will have a huge impact on prospects for spreading same-sex marriage to the 47 states that do not allow it.

Though Democrat Barack Obama was heavily favored to win the presidential race in California, the vote on the marriage amendment was expected to be close. A crucial question was how churchgoing black and Hispanic voters — presumably a pro-Obama constituency — would vote on the ballot measure.

Both Obama and his Republican rival, John McCain, say they oppose same-sex marriage. But Obama, unlike McCain, also opposes the California amendment and endorses the concept of broader rights for same-sex couples.

Ban-gay-marriage amendments also were on the ballot in Florida and Arizona, while Arkansas had a measure that would prohibit unmarried couples from adopting or being foster parents. Conservatives supporting the measure say it’s aimed at same-sex couples, who are able to adopt and be foster parents in most states.

South Dakota’s ballot included an initiative that would ban abortion except in cases of rape, incest and serious health threat to the mother. A tougher law without the rape and incest exceptions was defeated in 2006; a recent poll on the new version suggested the outcome was too close to call.

If it passed, it would likely trigger a legal challenge which could lead to the U.S. Supreme Court and a reconsideration of the 1973 Roe v. Wade ruling that established the right to abortion.

Colorado has an amendment that would define human life as beginning at conception. It doesn’t explicitly mention abortion, but activists on both sides in the campaign view it as a direct challenge to abortion rights.

Two other measures also have drawn the interest of the rival sides in the abortion debate — a California proposition that would require parental notification for a minor’s abortion and a Michigan initiative that would loosen restrictions on stem cell research.

Initiatives in Colorado and Nebraska would ban race- and gender-based affirmative action, similar to measures previously approved in California, Michigan and Washington. The movement’s leader, California activist-businessman Ward Connerly, says the candidacies of Barack Obama, Hillary Clinton and Sarah Palin prove blacks and women no longer need affirmative action.

In Washington state, voters were deciding whether to join Oregon as the only states offering terminally ill people the option of physician-assisted suicide.

State income taxes were targets in two states — a North Dakota initiative would cut income taxes by 50 percent for individuals and 15 percent for corporations, and a measure in Massachusetts would repeal the tax altogether.

Massachusetts also had measures that would ban dog racing and decriminalize possession of an ounce or less of marijuana. Use of marijuana for medical purposes would become legal under a measure in Michigan.

Among the other ballot items:

—Measures inspired by unease over immigration would designate English as the official language of government proceedings in Missouri and limit teaching of students in languages other than English to no more than two years in Oregon.

—A Missouri measure would require the state to generate 15 percent of its electricity from clean energy by 2021. A California measure would require all utilities to generate 20 percent of their power from renewable energy by 2010, and 50 percent by 2025.

—Another California measure would authorize the sale of $9.95 billion in bonds to fund a high-speed rail line between Los Angeles and San Francisco. It would be the most ambitious state rail project ever.