A former police officer turned lawmaker is launching the fourth effort this year to legalize recreational marijuana for Maine adults.

Rep. Mark Dion, D-Portland, has submitted a bill that would regulate recreational marijuana sales, tax them at 15 percent and allow use by adults 21 and older. The language of the legislation is being developed and details won’t be available until the process is completed.

Rep. Mark Dion says his plan would limit the number of retail pot stores so they aren’t “on every corner.”

Dion’s bill joins three other proposals – one from a fellow lawmaker and two from political action committees formed to advocate for legalization – that would legalize pot use by adults, create a regulatory structure for retail stores and cultivators, and tax sales.

“Although there are three other possible initiatives considering the legalization of marijuana, the proposal I’m bringing forward is more conservative,” said Dion, who was Cumberland County sheriff for 12 years and a Portland police officer for 21 years. “My goal is to treat this in the same way we provide oversight and control of alcohol.”

Dion said details, such as how much marijuana adults could possess, are being worked out, but his plan would create three tiers of licenses for cultivators. He also wants to limit the number of retail stores in Maine to 20 so the state doesn’t replicate other states where there are pot stores “anywhere and everywhere,” he said.

“I don’t think the parents I’ve talked to want to see a marijuana outlet on every corner or in every shopping mall,” Dion said.

Paul McCarrier, president of Legalize Maine, said he is looking forward to seeing the language of Dion’s proposal and that the bill will not derail Legalize Maine’s efforts to collect signatures to put the question to voters on the 2016 ballot.

“I think this shows there’s a lot of momentum to legalize marijuana,” he said.

Scott Gagnon, director of Smart Approaches to Marijuana Maine, which opposes marijuana legalization, said that despite the number of legalization proposals, he hears frequently from parents and educators who don’t want to see marijuana retail stores in their communities.

“Whether it’s 20 stores or 100 stores, at the end of the day we’re creating more places for kids to get access to marijuana,” he said.

Dion’s bill is backed by the Maine Association of Dispensary Owners. Becky DeKeuster, secretary of the association and co-founder of Wellness Connection, said the bill expands on the state’s successful medical marijuana program.

“We feel like what (Dion’s) bill does is take a piece of the existing medical framework that is very successful and well-regulated by the state and builds on that,” she said.

Dion said his proposal gives existing dispensaries preference when transitioning into the recreational market, although there also would be cultivation licenses available for others, including caregivers who currently provide medical cannabis to patients.

Rep. Diane Russell, D-Portland, also has submitted a marijuana legalization bill, though details of her plan will not be released until the bill’s language is completed in April, she said.

Last week, the Campaign to Regulate Marijuana Like Alcohol – backed by the Marijuana Policy Project, which advocated for legalization in Colorado – unveiled its proposal to allow adults to possess up to an ounce of marijuana, grow their own plants and set up a system for retail stores and commercial cultivation. That group also aims to get the legalization question on the 2016 ballot.

In February, Legalize Maine submitted to the Secretary of State’s Office an application for a citizens initiative that also seeks to legalize and regulate marijuana. Legalize Maine touts its proposal as a “homegrown” plan that focuses on supporting cannabis agriculture and small-scale growers.

To qualify for the ballot, each group must collect 61,123 valid signatures, or 10 percent of the total votes cast for governor last November, by Feb. 1, 2016.

Marijuana remains illegal under federal law, but Colorado and Washington state legalized the drug for recreational use in 2012. Last year, Oregon, Alaska and Washington, D.C., approved measures to legalize recreational pot.

Russell, who has presented legalization legislation for the past three years, said now is the time for Maine lawmakers to set the policy for legal marijuana use.

“I hope the Legislature does the right thing and realizes that the chaos that is happening (with multiple proposals) doesn’t need to be there,” she said. “If anything, I think the number of ways that legalization has come forward is indicative of just how ready Maine is to move forward on this.”

Dion, who previously served on the board of a dispensary, believes the time has come for lawmakers to approve a plan that properly regulates and taxes a substance people are already using. He said legalizing marijuana also would allow law enforcement to focus on “real problems” like heroin and methamphetamines.

David Boyer, manager of the Campaign to Regulate Marijuana Like Alcohol, said his group is “excited that there’s enthusiasm from all over to end marijuana prohibition and to stop punishing adults for using a substance that’s objectively safer than alcohol.”