WASHINGTON » Despite 75 years of federal marijuana prohibition, the Justice Department said today that states can let people use the drug, license people to grow it and even allow adults to stroll into stores and buy it — as long as the weed is kept away from kids, the black market and federal property.

In a sweeping new policy statement prompted by pot legalization votes in Washington and Colorado last fall, the department gave the green light to states to adopt tight regulatory schemes to oversee the medical and recreational marijuana industries burgeoning across the country.

The action, welcomed by supporters of legalization, could set the stage for more states to legalize marijuana. Alaska is scheduled to vote on the question next year, and a few other states plan similar votes in 2016.

The policy change embraces what Justice Department officials called a "trust but verify" approach between the federal government and states that enact recreational drug use.

In a memo to all 94 U.S. attorneys’ offices around the country, Deputy Attorney General James Cole said the federal government expects that states and local governments authorizing "marijuana-related conduct" will implement strong and effective regulatory and enforcement systems that address the threat those state laws could pose to public health and safety.

"If state enforcement efforts are not sufficiently robust … the federal government may seek to challenge the regulatory structure itself," the memo stated.

The U.S. attorney in Colorado, John Walsh, said he will continue to focus on whether Colorado’s system has the resources and tools necessary to protect key federal public safety interests.

Colorado Gov. John Hickenlooper said the state is working to improve education and prevention efforts directed at young people and on enforcement tools to prevent access to marijuana by those under age 21. Colorado also is determined to keep marijuana businesses from being fronts for criminal enterprises or other illegal activity, he said, and the state is committed to preventing the export of marijuana while also enhancing efforts to keep state roads safe from impaired drivers.

Under the policy, the federal government’s top investigative priorities range from preventing the distribution of marijuana to minors to preventing sales revenue from going to criminal enterprises, gangs and cartels and preventing the diversion of marijuana outside of states where it is legal under state law.

Other top-priority enforcement areas include stopping state-authorized marijuana activity from being used as a cover for trafficking other illegal drugs and preventing violence and the use of firearms in the cultivation and distribution of marijuana. The top areas also include preventing drugged driving, preventing growing marijuana on public land and preventing marijuana possession on federal property.

The Justice Department memo says it will take a broad view of the federal priorities. For example, in preventing the distribution of marijuana to minors, enforcement could take place whenmarijuana trafficking takes place near an area associated with minors, or when marijuana is marketed in a manner appealing to minors or diverted to minors.

Following the votes in Colorado and Washington last year, Attorney General Eric Holder launched a review of marijuana enforcement policy that included an examination of the two states. The issue was whether they should be blocked from operating marijuana markets on the grounds that actively regulating an illegal substance conflicts with federal drug law that bans it.

Last December, President Barack Obama said it doesn’t make sense for the federal government to go after recreational drug users in a state that has legalized it. Last week, the White House said that prosecution of drug traffickers remains an important priority.

A Pew Research Center poll in March found that 60 percent of Americans think the federal government shouldn’t enforce federal anti-marijuana laws in states where its use has been approved. Younger people, who tend to vote more Democratic, are especially prone to that view. But opponents are worried these moves will lead to more use by young people. Colorado and Washington were states that helped re-elect Obama.

"Today’s announcement demonstrates the sort of political vision and foresight from the White House we’ve been seeking for a long time," said Ethan Nadelmann, executive director of the Drug Policy Alliance, a New York-based group. "The White House is basically saying to Washington and Colorado: Proceed with caution."

Dan Riffle of the Marijuana Policy Project, the nation’s largest marijuana policy organization, called the policy change "a major and historic step toward ending marijuana prohibition" and "a clear signal that states are free to determine their own policies."

Kevin Sabet, the director of Project Smart Approaches to Marijuana, an anti-legalization group, predicted the new Justice Department policy will accelerate a national discussion about legalization because people will see its harms — including more drugged driving and higher high school dropout rates.

Johnson reported from Seattle. Associated Press writer Kristen Wyatt in Denver contributed to this report.