Voters in Colorado and South Dakota rejected ballot measures Tuesday that could have led to sweeping bans of abortion, and Washington became only the second state - after Oregon - to offer terminally ill people the option of physician-assisted suicide.

In California, exit polls and partial returns suggested a close race on a high-profile measure that would ban gay marriage - the first time such a vote has taken place in state where such unions are legal. Three other states enacted measures to curtail the rights of same-sex couples.

For the abortion rights movement, it was a day of relief and celebration.

A first-of-its-kind measure in Colorado, which was defeated soundly, would have defined life as beginning at conception. Its opponents said the proposal could lead to the outlawing of some types of birth control as well as abortion.

The South Dakota measure would have banned abortions except in cases of rape, incest and serious health threat to the mother. A tougher version, without the rape and incest exceptions, lost in 2006. Anti-abortion activists thought the modifications would win approval, but the margin of defeat was similar, about 55 percent to 45 percent of the vote.

"The lesson here is that Americans, in states across the country, clearly support women's ability to access abortion care without government interference," said Vicki Saporta, president of the National Abortion Federation.

In Washington, voters gave solid approval to an initiative modeled after Oregon's "Death with Dignity" law, which allows a terminally ill person to be prescribed lethal medication they can administer to themselves. Since Oregon's law took effect in 1997, more than 340 people - mostly ailing with cancer - have used it to end their lives.

Elsewhere, the marijuana reform movement won two prized victories, with Massachusetts voters decriminalizing possession of small amounts of the drug and Michigan joining 12 other states in allowing use of pot for medical purposes.

Henceforth, people caught in Massachusetts with an ounce or less of pot will no longer face criminal penalties. Instead, they'll forfeit the marijuana and pay a $100 civil fine.

The Michigan measure will allow severely ill patients to register with the state and legally buy, grow and use small amounts of marijuana to relieve pain, nausea, appetite loss and other symptoms.

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

Similar measures had prevailed in 27 states before Tuesday's elections, but none were in California's situation - with thousands of gay couples already married following 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 won the presidential race in California on his way to wrapping up the White House, the vote on same-sex marriage leaned toward instituting the ban in early returns. A crucial question was how churchgoing black and Hispanic voters - presumably a pro-Obama constituency - would vote on the ballot measure.

According to exit polls, blacks were far more likely than whites or Hispanics to support the ban. Age also was a key factor - the exit polls showed voters under 30 opposing the ban by a 2-to-1 ratio, while most voters 60 and older supported the ban.

Obama opposed the California amendment and endorses the concept of broader rights for same-sex couples.

Amendments to ban gay marriage were approved in Arizona and Florida, and gay rights forces also suffered a loss in Arkansas, where voters approved a measure banning unmarried couples from serving as adoptive or foster parents. Supporters made clear that gays and lesbians were their main target.

Nebraska voters, meanwhile, approved a ban on race- and gender-based affirmative action, similar to measures previously approved in California, Michigan and Washington. Returns in Colorado on a similar measure were too close to call.

Ward Connerly, the California activist-businessman who has led the crusade against affirmative action, said Obama's victory proved his point. "We have overcome the scourge of race," Connerly said.

Energy measures met a mixed fate. In Missouri, voters approved a measure requiring the state's three investor-owned electric utilities to get 15 percent of their electricity from renewable sources by 2021. But California voters defeated an even more ambitious measure that would have required the state's utilities to generate half their electricity from windmills, solar systems, geothermal reserves and other renewable sources by 2025.

Two animal-welfare measures passed - a ban on dog racing in Massachusetts, and a proposition in California that outlaws cramped cages for egg-laying chickens.

Amid deep economic uncertainty, proposals to cut state income taxes were defeated decisively in North Dakota and Massachusetts.

In San Francisco, an eye-catching local measure - to bar arrests for prostitution - was soundly rejected. Police and political leaders said it would hamper the fight against sex trafficking.