NEW YORK -- Voters in three states will decide next month whether to legalize the sale and use of marijuana. If a ballot measure in one of those states succeeds, as supporters predict, it may create a rare truce in the war on drugs -- and trigger a showdown with the federal government.

State-level legalization would climax decades of struggle by reformers to convince voters that marijuana presents less of a threat to public safety than legal drugs, including alcohol. It would also show that pro-pot activists have learned from previous losses, like California's Proposition 19.

"There's no doubt in my mind that at least one of them will pass," said Dan Riffle, a legislative analyst for the Marijuana Policy Project.

His confidence appears justified. A September poll put support in Washington state at 57 percent. A Colorado poll out Monday from The Denver Post showed 48 percent in favor, versus 43 percent opposed. Support in Oregon was lagging.

Proponents have picked their battles. Legalization is only on the ballot in libertarian-leaning western states. Still-hostile state legislatures have been bypassed with ballot initiatives. And the presidential election will draw marijuana- friendly younger voters to polls.

Public support for marijuana legalization has been on a long-term upward curve, with a majority of Americans saying for the first time last year they favored it.

Translating that sentiment into success at the ballot box, however, has been difficult. Medical marijuana has the public relations advantage of using cancer victims as spokespersons. But legalizing marijuana for all adults has often been defined by opponents, who raised the specter of drug dealers and impaired drivers in California in 2010.

So in Washington state, where legalization is most likely to be approved, reformers carefully crafted the initiative to account for concerns from law enforcement officials. They have also made heavy use of former U.S. Attorney John McKay, who speaks credibly to public safety concerns.

"Essentially it was about building a relationship of trust," said Allison Holcomb, drug policy director for the state chapter of the American Civil Liberties Union, who leads the campaign to pass the legalization ballot measure, known as Initiative 502.

The ACLU carefully poll-tested provisions of the initiative. An intoxication standard for marijuana's intoxicant was created to defuse concerns about users driving under the influence. Instead of leaving regulation up to municipalities, as would have been done under California's failed proposition, a single, statewide standard would be put in place.

The "libertarian wet dream of legal pot with no regulations" does not play well with voters, said Riffle.

Rather, people want safeguards. They also want to see a different kind of green. All three measures emphasize taxing marijuana sales to produce revenue for cash-strapped states. In Washington alone, the state's Office of Financial Management estimated that legalization could bring as much as $2 billion over five years in taxes.

Nothing in the evolution of the pro-pot movement will deter legalization opponents from trying to stop the ballot measures.

In Colorado, support for legalization seems to have dipped since last month. That's not unusual for ballot measures as Election Day approaches. But Laura Chapin, the spokeswoman for No on 64, said it shows her side's arguments are winning.

"I think a lot of that is due to people understanding that amending the Colorado Constitution to fully legalize recreational marijuana and create a marijuana industry in this state brings with it a lot of problems," Chapin said.

Marijuana opponents in Colorado have pointed to the standard issues of health and safety, but Chapin said they have also highlighted the appropriateness of the amendment method. "This is a case where the how matters as much as the why."

Nationally, drug warriors warn of a "constitutional confrontation" if states legalize marijuana sales.

"Federal law, the U.S. Constitution and the Supreme Court decisions say that this cannot be done, because federal law preempts state law," said Peter Bensinger, who headed the Drug Enforcement Administration under Presidents Gerald Ford, Jimmy Carter and Ronald Reagan.

The Obama administration has rejected legalization in the past. but this election season, it has been silent on the topic. Pro-pot activists acknowledge that if President Barack Obama -- or Mitt Romney -- wanted to stop the collection of marijuana tax revenue, they likely could.

"There's a whole regulatory structure that this sets up, and if the federal government so chooses they can interfere with that," said Riffle. But he warned that if the feds did so, they would clash with the will of voters in the "laboratories of democracy" -- and against a very popular earmark in the Colorado measure.

"Essentially every action from the federal government there would mean hundreds of millions of dollars that wouldn't go to schools," Riffle said.

Voters, so far, seem unconcerned by the prospect of federal action. Travel author and television personality Rick Steves, a supporter of the Washington measure, said he has received support from across the political spectrum during his barnstorming tour of the state.

Steves pointed to Portugal, where problematic drug use has reportedly dropped by half since drugs were decriminalized in 2001, as an example of the positive change. And no, he added, Washington state will not start to look like another European destination if it legalizes marijuana.

"I don't foresee any Amsterdam kind of mecca here," Steves said. "I just see less people in jail and more social justice."

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