An unprecedented marijuana-legalization measure in California trailed in early returns Tuesday after a spirited campaign that pitted the political and law enforcement establishment against well-funded activists seeking to end the prohibition of pot.

With 10 percent of the votes counted, the "No" side had 56 percent of the vote.

It was by far the highest-profile of the 160 ballot measures being decided in 37 states. Other measures dealt with abortion, tax cuts and health care reform.

On a night of conservative advances in much of the country, Massachusetts voters spurned a chance to cut their taxes _ rejecting a proposal to lower the state sales tax from 6.25 percent to 3 percent. Critics, including all four candidates for governor, said the cut would have forced the state to slash $2.5 billion in services, including local aid to cities and towns.

In Oklahoma, voters overwhelmingly passed three measures that had dismayed some progressive and immigrants-rights groups. One makes English the state's "common and unifying language," another requires a government-issued photo ID in order to vote, and the third prohibits state courts from considering international law or Islamic law when deciding cases.

California's marijuana proposal _ titled the Regulate, Control and Tax Cannabis Act _ would allow adults 21 and over to possess up to an ounce of pot, consume it in nonpublic places as long as no children were present and grow it in small private plots.

The initiative, Proposition 19 on the state ballot, also would authorize local governments to permit commercial pot cultivation, as well as the sale and use of marijuana at licensed establishments.

Proponents have pitched it as a sensible, though unprecedented, experiment that would provide much-needed revenue for the cash-strapped state, dent the drug-related violence in Mexico by causing pot prices to plummet and reduce marijuana arrests that they say disproportionately target minority youth.

The state branches of the NAACP and the League of United Latin American Citizens have endorsed it, as have several retired police chiefs. Several California cities have companion measures on their local ballots that would tax retail marijuana sales if the measure passes.

Although marijuana already is available at storefront medical marijuana dispensaries in California, Prop 19 trailed in recent opinion polls. Every major newspaper, both political parties, the two candidates for governor and all but a handful of leading politicians have come out against it.

Federal officials said they would continue enforcing laws against marijuana possession and sales, and have not ruled out suing to overturn the California initiative if it passes.

Prop 19 supporters were buoyed by a new Gallup poll showing that national support for legalizing marijuana has reached an all-time high of 46 percent. Gallup said majority support could come within a few years if recent trends continue.

"No matter what happens (with Prop 19), it's now undeniable that national public sentiment is increasingly turning against the idea that responsible adults should be criminalized for using a substance less harmful than alcohol," said Rob Kampia of the Marijuana Policy Project. "We are already looking forward to achieving major victories in 2012."

In South Dakota, voters rejected a measure to legalize medical marijuana _ a step already taken by California and 13 other states. A medical marijuana measure also was on Arizona's ballot, and Oregon voters were deciding whether to expand the state's current medical marijuana law by authorizing state-licensed dispensaries.

Among other notable ballot issues on Tuesday:

_In the littlest state, voters chose to keep the longest formal name _ opting to stay as Rhode Island and Providence Plantations, instead of just Rhode Island.

_In Illinois, where the two most recent former governors have been convicted on federal charges, voters approved an amendment that enable future governors to be recalled by popular vote.

_Oklahoma voters approved a proposed amendment aimed at nullifying the segment of the new federal health care law requiring people to have health insurance. Similar measures were on the ballots in Arizona and Colorado.

_In Colorado, political leaders of both major parties opposed three measures to ban borrowing for public works, cut the income tax and slash school district property taxes. Opponents said the proposals would cost the state $2.1 billion in revenue and eliminate tens of thousands of jobs.

_For the first time since the 1990s, there were no measures to ban same-sex marriage. But in Iowa, voters were deciding whether to oust three state Supreme Court justices who joined a unanimous 2009 ruling that legalized gay marriage there.

_Washington state's voters had a chance to repeal taxes on candy, soda and bottled water adopted by lawmakers last year, which would eliminate a projected $352 million in revenue over five years. Another proposal would impose a state income tax on any income above $200,000, or $400,000 for couples.

_Colorado voters were deciding on an anti-abortion "personhood" amendment _ similar to one rejected in 2008 _ that would give unborn fetuses human rights in the state constitution.

_California's Proposition 23 would suspend the state's landmark greenhouse gas emissions law until the jobless rate falls to 5.5 percent for a year. It is backed by out-of-state oil companies; foes include Gov. Arnold Schwarzenegger and alternative-energy entrepreneurs.

_An Arizona measure would ban affirmative action programs by state and local governments based on race, ethnicity or sex.

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David Crary reported from New York.