DENVER — For supporters of legalizing marijuana, it was a historic moment, one that drew comparisons to the end of Prohibition: On Tuesday, voters in Colorado and Washington State made it legal to smoke pot recreationally, without any prescription or medical excuse.

But as Gov. John Hickenlooper of Colorado cautioned voters on Tuesday night: “Don’t break out the Cheetos or the Goldfish too quickly.”

For one thing, it will be a month before the measures are officially on the books, and longer still before state officials write the rules, tax codes and other regulations creating new state-licensed retail marijuana shops. But the larger, looming problem is a clash with the federal government, which still views marijuana as a Schedule I prohibited substance and has cracked down on states, like California and Montana, that have voted to allow medical marijuana.

In a statement on Wednesday, a spokesman for the Drug Enforcement Agency said the Justice Department was reviewing the ballot measures and declined to comment directly on how officials would respond to them. But he said the agency’s enforcement of federal drug laws “remains unchanged.” The United States attorneys in Denver and Seattle responded with nearly identical statements, offering no clue on whether they would sue to block the measures from being put into effect.