A proposed initiative to legalize limited possession of marijuana in Colorado needs more signatures to qualify for the ballot.

The Colorado Secretary of State’s office announced today that the campaign collected only 83,696 valid signatures. It needs 86,105 to qualify.

The campaign will now have 15 days to collect the remaining 2,409 valid signatures. Mason Tvert, one of the initiative’s proponents, said in a statement today that the announcement was unexpected but “just a very small bump in the road.”

“We are confident we will complete this process successfully and qualify the initiative for the ballot,” Tvert said.

Last month, the campaign turned in more than 160,000 signatures in boxes of petitions. But, after reviewing a sample of those signatures, the Secretary of State’s office could not conclusively project whether there were enough valid signatures on the petitions for the initiative to qualify.

That meant the Secretary of State’s office needed to go line-by-line through the petitions, verifying each signature. Today was the deadline to complete that task.

The initiative, a proposed constitutional amendment, would legalize possession of up to one ounce of marijuana for people 21 and older. It would also allow people to grow a small number of marijuana plants in their homes.

The measure would also allow for people to open marijuana retail shops, but it would give communities the ability to ban those businesses. Lastly, it would legalize the growing of industrial hemp.

All such activities would remain illegal under federal law.

The initiative — for now known as Proposed Initiative No. 30 and dubbed by the campaign The Regulate Marijuana Like Alcohol Act of 2012 — is one of three separate proposed measures for the 2012 ballot that would legalize marijuana in Colorado.

Another, from Cannabis University of Colorado head Michelle LaMay, would prohibit judges from imposing penalties on anyone for marijuana possession of any amount. Supporters call the initiative The Relief for the Possession of Cannabis Act. The campaign behind it has announced it will begin collecting signatures this month.

Meanwhile, a third initiative was filed Thursday. That measure, which supporters call Legalize 2012, would create in Colorado’s constitution a fundamental right to use and possess any amount of marijuana for people over 18. It would allow for retail sales of marijuana “without restrictions that are onerous or burdensome.” It would require the state attorney general to file lawsuits to prevent the federal government from enforcing federal marijuana laws in Colorado. And it would create a state-funded commission that could help Colorado citizens facing federal marijuana prosecution with their defense.

That initiative has not yet had its first administrative hearing.

John Ingold: 303-954-1068 or jingold@denverpost.com

