(Reuters) - Supporters of legalizing marijuana for recreational use have submitted enough signatures to put the matter to voters in Washington state in a bold move that, if successful, could put Olympia on a collision course with the federal government.

The group New Approach Washington submitted nearly 278,000 valid signatures for the measure, more than required to put it on the November ballot, David Ammons, a spokesman for the Washington Secretary of State's office, said in a statement.

The move comes as federal prosecutors have sought to crank up pressure on several mostly western states, including Washington, that have legalized medical marijuana even as cannibis remains classified as an illegal narcotic under federal law.

The proposal, if approved by voters, would allow marijuana sales to people 21 and older, permit state taxes to be collected on the drug, ban pot advertising and prohibit driving under the influence of cannabis.

Supporters of legalizing marijuana, who include acting Seattle city attorney Peter Holmes, say the federal prohibition on the drug has not curbed use and that it enriches drug cartels.

"This is the grown-up approach to regulating a relatively harmless drug," Holmes said.

Opponents of legalization say it would lead to more abuse of the drug, including by young people, and that underground sales would continue.

"There will always be a black market. That's been proven with cigarettes with the tobacco industry," said Calvina Fay, head of the Florida-based Drug Free America Foundation. "Even though tobacco is legal and it's regulated, there's still a huge global black market."

Washington is one of 16 states that, along with the nation's capital, have decriminalized medical marijuana. But federal agents have raided medical marijuana dispensaries in several states, including Washington, in recent months.

Under state law, the recreational legalization initiative next heads to the Washington State Legislature, which has the option of avoiding a popular vote by itself enacting the proposal to legalize marijuana, Ammons said.

The legislature could also allow the measure to go to the ballot alongside an alternative from lawmakers, Ammons said.

Alison Holcomb, campaign director of New Approach Washington, has said she did not expect the legislature would enact the proposal on its own, but would leave the issue for voters to decide.

In 2010, a measure to legalize marijuana in California lost at the ballot box when less than 47 percent of voters approved it.

No modern, affluent nation has ever legalized commercial production and distribution of marijuana, according to research organization RAND Corp.

In the Netherlands, famous for its Amsterdam cafes where guests buy and smoke marijuana, authorities allow adults to buy the drug but the country officially has a policy that commercial production of it is illegal, said Beau Kilmer, co-director of the RAND Drug Policy Research Center.

(Reporting By Alex Dobuzinskis; Editing by Cynthia Johnston)

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