HILO, Hawai'i — Police and law enforcement officials are still mulling how to respond to an initiative passed by Big Island voters that orders police to make arrests of adults for possession of small amounts of marijuana their lowest priority.

The measure, which was advanced by a group called Project Peaceful Sky, also prohibits the county from accepting state or federal grant money to pay for marijuana eradication operations.

Helicopter missions to yank up marijuana plants have long been a sore point in rural areas of the Big Island, with some residents complaining the helicopter raids are a noisy intrusion on their civil liberties.

Supporters of the initiative argue that making marijuana enforcement the lowest police priority will free up police resources to deal with more serious crimes.

The initiative was approved by a hefty margin, with 53 percent voting in favor, less than 39 percent voting against the ballot measure, and about 8 percent leaving their ballots blank.

Big Island police have not altered any of their operating procedures so far because of the new ordinance, according to a spokeswoman for the department.

"We're still discussing the issue with prosecutors and corporation counsel to determine what we need to do, and how we need to go about it," said Chris Loos, public relations specialist with the Big Island Police Department.

A spokesman for the federal Drug Enforcement Administration has said the initiative won't alter the DEA's enforcement efforts, and said federal agents will continue to enforce anti-drug laws and target growers and distributors.

The ordinance requires that "the cultivation, possession and use for adult personal use of cannabis shall be the lowest law enforcement priority for law enforcement agencies in the County of Hawai'i." It applies to adult personal users on private property, with "personal users" defined as people who have less than 24 plants or 24 ounces of marijuana.

County Corporation Counsel Lincoln Ashida has publicly questioned the legality of the initiative, arguing it might be unenforceable because it apparently violates the pre-emption doctrine arising from the U.S. and state constitutions.

That doctrine says legislative bodies such as the County Council cannot dictate to executive-branch agencies such as police and prosecutors how to run their day-to-day operations.

In an e-mailed response to questions, Ashida said police "could simply opt to ignore this initiative for the reason that it is in direct contravention to federal and state law."

On the other hand, Ashida wrote, "our office always encourages our client departments to work with the public to address their concerns as well as provide them as much information as possible. In this case, we must further recognize and respect the will of the voters, and attempt to reconcile the preemption (supremacy clause) issue."

If the legal questions can't be resolved, Ashida said, the ordinance created by the ballot initiative may remain on the books but never be enforced. That happened with other ordinances such as the county prohibition on transporting or storing radioactive material on the Big Island, which can't be enforced because it is pre-empted by federal law, he said.

Ashida said police and prosecutors could also seek an opinion from the state attorney general on whether the initiative is legal.

Not everyone agrees the ordinance is likely to be ruled illegal. Adam Wolf, staff attorney with the American Civil Liberties Union's national Drug Law Reform Project, said there has so far been only one legal challenge to similar "lowest priority" ordinances for marijuana enforcement in the 13 jurisdictions that adopted them.

That case was in Santa Barbara, Calif., and Wolf said a Santa Barbara Superior Court judge rejected the pre-emption argument Ashida raises.

Wolf said the Big Island is in the "mainstream" in passing the ballot measure, and "the people should demand that their government follow the law. The people should hold their government accountable to respect people's rights, and the government's obligations."