DENVER – Colorado voters will decide this fall whether to legalize marijuana for recreational use when the state becomes the second in the nation to put such a proposal on ballots this year.

The Secretary of State’s Office said Monday that supporters of the legalization initiative collected enough signatures to get their measure before voters, meaning Colorado will join Washington state in putting a recreational pot question on November ballots.

Voters will be asked whether adults older than 21 should be allowed to use marijuana even without a doctor’s recommendation. The measure would allow adults to have up to 1 ounce of marijuana or six marijuana plants. The proposal also allows for commercial pot sales, although cities and counties would have permission to ban marijuana sales if they choose.

The plan would also direct state lawmakers to put an undetermined excise tax on pot, with the proceeds going to education.

Colorado considered and rejected recreational pot legislation in 2006. But activists say Colorado residents have since become accustomed to medical marijuana and are more willing to consider full legalization.

“The people of Colorado are ready to end marijuana prohibition and begin taxing it and regulating it like alcohol,” said Mason Tvert, head of Colorado’s Campaign To Regulate Marijuana Like Alcohol.

The campaign needed two tries to make the ballot. Last month, the initiative backers fell just short of the required 86,000 signatures when tens of thousands were deemed invalid. But officials said a second attempt allowed under Colorado law left the campaign with more than 90,000 valid signatures.

Compared to Washington state, Colorado officeholders have been slow to embrace recreational legalization.

Seattle Mayor Mike McGinn has backed recreational legalization in Washington state. But no current Colorado elected official was scheduled to join legalization activists at a news conference today.

Despite the chilly reception from public officials, marijuana activists say the time is right for legalization. “This could be a watershed year in the decades-long struggle to end marijuana prohibition in this country,” said Art Way, Colorado manager of the Drug Policy Alliance.

The measure would set up a direct federal showdown over drug laws, but Colorado and 16 other states already buck the federal government by allowing marijuana for medical use.