Cliff DesPeaux / Reuters

The drive to legalize marijuana has long been a fringe cause, associated with hard-core libertarians and college-age stoners. But it could go mainstream in a big way in this November’s election, when Washington could become the first state to legalize recreational pot use. If it does — or if voters in any of several other states do — this year could be a turning point in the nation’s treatment of marijuana.

The idea that a majority of voters could support legalizing marijuana may seem far out — but the polls say otherwise. In many states, the prolegalization and antilegalization camps are roughly equal in size. In a poll of Washington state voters released last month, supporters of the legalization referendum outnumbered opponents: 48% vs. 45%. And Washington probably won’t be the only state voting on marijuana this year. In Colorado, supporters last week fell about 3,000 signatures short of getting a legalization measure on the ballot — but the law gave them 15 days to collect the rest, and it seems likely they will. Activists are also collecting signatures in other states, including California, Michigan and Montana.

For years, the debate over marijuana has been focused on a narrower question: medical marijuana. The argument that cancer patients and others with chronic pain should be able to alleviate it by using marijuana has been prevailing in state after state. Today, 16 states — including Washington and Colorado — and the District of Columbia have legalized marijuana for medical purposes.

(MORE: Study: Legal Medical Marijuana Doesn’t Encourage Kids to Smoke More Pot)

Recently, the action has shifted to recreational marijuana use. Washington’s referendum would treat pot much like alcohol, so the sale of marijuana would be restricted to people over 21. The new law would give the Liquor Control Board the authority to license marijuana farms, and marijuana tax revenues would be directed to health and drug-abuse prevention programs.

But other states’ proposed laws are more laissez-faire. Colorado would legalize marijuana so that, as its supporters put it, cannabis would be regulated like “grapes, tomatoes or other harmless botanical plants.” Montana’s amendment focuses on decriminalizing marijuana but leaves it to the legislature to work out the details.

Supporters argue that legalization is long overdue. They argue that it is no more harmful than alcohol or tobacco — and that in a free country people should be able to decide on their own whether to use it. They also argue that, as a practical matter, laws against marijuana have been no more successful than Prohibition was against alcohol — and that, similarly, it has given criminals a monopoly on distributing and selling it. Legalization, they say, would reduce the number of people in prison, and it would shift revenue from drug syndicates to government in the form of tax receipts.

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Not surprisingly, the legalization drives have drawn heated opposition. Critics argue that marijuana is harmful and addictive — and that it is often a gateway drug, leading to cocaine or heroin. They say stoned drivers would be a menace on the roads. And they warn that if it were legalized and readily available, marijuana use could soar. (The University of Michigan’s “Monitoring the Future” survey reported that daily marijuana use is already at a 30-year high among high school seniors, even as alcohol use has been declining.) The anticamp also argues that marijuana is stronger than it was decades ago — from two to 10 times stronger, some experts say. (Other experts dispute the figures.)

If Washington or some other state legalizes marijuana, that would not settle the matter. It would still be a controlled substance under federal law. And the U.S. Constitution’s Supremacy Clause says that when federal and state laws clash, federal law trumps. As a practical matter, though, the federal government does not have the resources to police everyday use of marijuana. If states begin to legalize it, the federal government might be hard-pressed to justify diverting limited Drug Enforcement Agency resources away from heroin cartels toward small-time pot smokers.

It is hard to handicap this year’s voting, but one possibility is this: marijuana legalization could lose in Washington and Colorado in November, but recreational use could nonetheless be headed toward legalization in many states in the not-too-distant future. Support for legalization has been rising steadily, from just 12% in 1970 to 31% in 2001 to 50% today, with young people (ages 18-29) the most in favor (62%) and older people (ages 50-64) the least (49%).

In strictly political terms, this is a powerful combination: fast-growing support and solid majorities among the young, who represent where the electorate is headed. (Support for gay marriage polls similarly — which is why it is becoming law in more states.) In a few years, the national discussion may well turn from whether to legalize marijuana to how to do it in the most prudent way.

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