WASHINGTON (AP) — Despite 75 years of federal marijuana prohibition, the Justice Department said Thursday 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.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.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.