The city, in a novel lawsuit seeking to block U.S. Officials from forcing the dispensary to close, says the federal government's own scientists have found medical benefits for pot and have secured a U.S. patent for use of the drug, even as prosecutors have targeted medical cannabis dispensaries.

"In the (federal) government's world, there is no science," Cedric Chao, who represents Oakland in the case pro bono, told the judge on Thursday.

The legal fight before U.S. Magistrate Judge Maria-Elena James centers on Harborside Health Center, an Oakland outfit that bills itself as the world's largest medical marijuana dispensary and was featured in the Discovery Channel television series "Weed Wars."

The legal tussle comes amid a growing federal-state battle over marijuana that intensified when states in the U.S. West and Northeast liberalized medical pot laws in recent years, setting the stage for voters in Colorado and Washington in November to approve legalizing recreational use of the drug as well.

The federal government, which holds that medical marijuana is illegal and that the drug is liable to be abused, in July initiated civil forfeiture actions against landlords of Harborside for the center's two properties, in an effort to force the operation to close.

Oakland's lawsuit, filed in October, seeks an injunction to halt federal prosecutors' efforts to shutter Harborside, which will generate an estimated $1.4 million in sales tax revenues for the city this year. It has been rare for any municipality to challenge the federal government over crackdowns on medical pot.

FEDS VS FEDS?

Chao criticized the federal government's classification of marijuana as an illegal drug without medicinal value.

In court papers filed earlier this month, he cited a 2003 cannabis-related patent obtained by the federal government. He argued the government's own scientists "continuously discover new benefits" for medical pot and that it has "sought exclusive ownership rights to cannabis compounds."

That calls into question the government's efforts to bar groups such as Harborside from selling the drug, he said.

But Special Assistant U.S. Attorney Arvon Perteet argued that federal law takes precedence over the state's 1996 voter-approved measure allowing medical marijuana, and that the federal government is within its authority to target Harborside.

"They can sell popcorn there, candy," Perteet told the judge. "They cannot use the property for any illegal purposes."

Judge James promised to decide as "quickly as possible" whether to allow Harborside to continue to operate while she considers Oakland's challenge to the federal crackdown. The operation says it has 100,000 patients.

Eighteen states, including California and the District of Columbia allow medical marijuana.

In response to Colorado and Washington state's moves to legalize recreational use of the drug, President Barack Obama last week told ABC News that federal authorities have more important priorities than targeting recreational marijuana users in those two states, given limited federal resources.

(Editing By Alex Dobuzinskis; editing by Todd Eastham)

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