Proponents of marijuana have argued for years that the drug is safer than alcohol, both to individuals and society. But a ballot proposal to legalize possession of marijuana in small amounts in Colorado, likely to be on the November ballot, is putting the two intoxicants back into the same sentence, urging voters to “regulate marijuana like alcohol,” as the ballot proposition’s title puts it.

Given alcohol’s long and checkered history - the tens of thousands of deaths each year, the social ravages of alcoholism - backers of the pro-marijuana measure concede there is a risk of looking as if they have cozied up too much, or are comparable, to old demon rum.

“Why add another vice, right?” said Mason Tvert, a co-director of the Campaign to Regulate Marijuana Like Alcohol, which has led the ballot drive. “But we’re not adding a vice; we’re providing an alternative.”

The goal of legalization, Mr. Tvert added, is not to make access to marijuana easier, but rather, “to make our communities safer by regulating this substance, taking it out of the underground market, controlling it and better keeping it away from young people.”

The debate here and in Washington State - where members of a pro-legalization group have also submitted what they say are more than enough signatures to secure a spot on the ballot - is premised on the idea that marijuana has become, if not quite mainstream, then at least no longer alien to the average voter. Medical marijuana is already legal in both states.

But greater familiarity with marijuana could be a double-edged sword, opponents say.

Medical marijuana dispensaries, especially in Colorado, have exploded in number in the last few years - some with medical-sounding names, others garishly suggestive in their names and imagery of the intoxicants on sale within. More than 88,000 Colorado residents have medical marijuana cards, according to the most recent state figures, with young men in their 20s and 30s - many of them suffering debilitating pain, according to their doctor-signed certificates - disproportionately represented.

And many Colorado communities have been actively debating medical marijuana - and saying no to it. Eighty-five Colorado communities have banned or halted openings of dispensaries, through popular vote or through their city councils or commissions, and where a municipality posed the question to voters, marijuana has lost 88.1 percent of the time, according to the Colorado Municipal League, an association of city governments.

The federal government, meanwhile, in states from California to Montana, has also been cracking down on medical marijuana growers and sellers who prosecutors say have gone beyond what their states allow.

Some critics of legalization say that medical marijuana’s growth, and the abuse of medicines that leak out to become recreational, foreshadows the dangers if accessibility is increased. Washington’s measure would be a statutory legal change, while Colorado’s would amend the State Constitution.

“It’s largely state-sanctioned fraud,” said Colorado’s attorney general, John W. Suthers, a harsh critic of the medical marijuana system who is speaking out against the ballot measure. “We have thousands and thousands of people lying to doctors, saying they have a debilitating medical condition.”

And some doctors are going along with the ruse, Mr. Suthers said, “practicing substandard medicine by actually closing their eyes.”

Supporters of legalization agree that medical marijuana - now legal in 16 states and the District of Columbia - has led to abuses, and that many voters are angry and disgusted with how things have unfolded. And that, they say, is the very problem that legalization would fix. Banning or improperly regulating a substance that large numbers of people will use anyway failed in the 1920s with alcohol - with the spread of speakeasies and corruption during Prohibition - and is failing now with marijuana, they say.

“People don’t like the hypocrisy and the disrespect for law,” said Alison Holcomb, the campaign manager for New Approach Washington, a group backing the ballot measure, called I-502.

But Ms. Holcomb said that hypocrisy was precisely where the comparisons with alcohol and Prohibition became apt. Millions of Americans disregarded the law in the days of Al Capone, and millions are doing so now with marijuana. “That’s what prohibition fosters,” she said. “We counter that not by going backwards, but by going forward.”

The specter of California’s vote in 2010, when voters rejected legalization, and 2006, when a similar measure failed in Colorado, hangs over this year’s debate. And there is also division among those for legalizing marijuana. One such group, Sensible Washington, is arguing to voters that passing I-502 would create a false sense of security for marijuana users, since possession still remains a federal crime.

The group also objects to a driving-under-the-influence standard in the proposal that it says would not fairly measure impairment, and that almost any medical marijuana patient would fail, hours and perhaps even days after consuming cannabis.

“We are greatly concerned that innocent people risk conviction, and are left without a defense,” Troy Barber, a steering committee member at Sensible Washington, said in an e-mail. “In fact, this issue has created a huge rift in the antiprohibition on cannabis movement in our state.”

But things in Colorado have also significantly changed in the six years since the last referendum here. Medical marijuana providers now have money to back campaigns with advertising - in stark contrast to the effort in 2006, which had almost no financial backing - and are mostly supporting the ballot drive, said Jason Lauve, a spokesman for the Association of Cannabis Trades for Colorado, a trade group for medical providers. State tax revenues from medical marijuana sales have risen sharply as well, up to $5 million for the year ending June 30, 2011, from $2.2 million for the year ending June 30, 2010.

The politics of the states’ rights movement, meanwhile, which holds that state authority should, in general, trump federal jurisdiction - argued by many libertarians and Tea Party groups - is adding its own quirky element to the mix.

Representative Ron Paul of Texas, the Republican presidential candidate, has made the argument for state authority on drug laws, among other issues, a repeated refrain of his campaign.

“I think the federal war on drugs is a total failure,” Mr. Paul said in a Republican presidential candidates’ debate in November.

“Why don’t we handle the drugs like we handle alcohol?” Mr. Paul asked. “Alcohol is a deadly drug.”

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By KIRK JOHNSON
DENVER