Medical marijuana advocates, decrying a federal government crackdown on dispensaries and a failure of state lawmakers to act, said Tuesday that they are drafting a 2012 ballot initiative to impose statewide oversight of California's burgeoning medicinal cannabis trade.

The ballot push, announced at a San Francisco news conference, is being readied by groups that include the architects of 2010's unsuccessful Proposition 19, which would have legalized marijuana for recreational use.

Dale Sky Jones, chancellor of Oakland's Oaksterdam University, the cannabis trade school that became the nerve center for the Proposition 19 campaign, said recent federal enforcement actions underscored a need for an initiative dealing specifically with regulating medical marijuana.

A representative for the United Food and Commercial Workers Unions, which is organizing California cannabis workers, and Steve DeAngelo, director of California's largest medical marijuana dispensary, said they are also working on drafting language for the potential 2012 initiative.

While they noted the framework is still to be determined, advocates said they are considering asking voters to impose a Colorado-style regulatory system, with state inspections and licensing, on medical marijuana cultivators and providers.

Jones, chairman of the Coalition for Cannabis Reform Policy, said the group hopes to build on the nearly 47 percent of voters who supported Proposition 19 to pass an initiative that would impose "a robust system of statewide regulation" for medical marijuana.

But backers will have to find funding sources other than Richard Lee, the Oaksterdam founder who contributed $1.5 million to Proposition 19. He has said he can't afford to bankroll another ballot measure.

Assemblyman Tom Ammiano, D-San Francisco, said the Legislature's inaction may have stoked federal intervention by leaving local governments to scramble to decide how to regulate hundreds of medical marijuana stores that have opened in California since 2009.

"Right now, zip is happening," Ammiano said at the San Francisco news conference that was called to protest federal actions on medical marijuana as President Barack Obama appeared at a political fundraiser in the city.

The president faced demonstrations Tuesday by anti-war activists and Occupy San Francisco protestors as well as the medical marijuana supporters.

"It's a slap in the face for all the people who voted for Proposition 215," the 1996 state Compassionate Use Act initiative legalizing medical marijuana use, Ammiano said. "California should not be lagging behind. We should be fighting back. Right now the state is dithering."

Ammiano and other advocates charged that Obama's Justice Department is launching an unfair assault on California medical marijuana providers. On Oct. 7, California's four U.S. attorneys announced charges against dispensaries and growers, as well as financial speculators throughout the state's medicinal pot market.

Declaring the state's purportedly nonprofit medical marijuana trade to be "hijacked by profiteers," federal authorities also have been threatening landlords with loss of their buildings or properties – and potential prosecution – for leasing to dispensaries or for marijuana cultivation.

At the gathering in San Francisco, Lynette Shaw, director of California's longest operating dispensary, the Marin Alliance for Medical Marijuana, called for Obama to issue an executive order stopping the California enforcement actions.

A recent letter from San Francisco U.S. Attorney Melinda Haag threatened the landlord of the dispensary, opened in 1996 and licensed by the city of Fairfax in 1997, with property seizure. It also said dispensary operators could be subject to charges resulting in up to 40 years in prison under federal laws against narcotics dealing within 1,000 feet of a park.

Matt Cohen, owner of the Mendocino County Northstone Organics medical marijuana farm, also appeared. His premises was raided by U.S. drug agents this month, even though his plants are tagged and monitored by the local sheriff under a county-supervised medical marijuana compliance program.

In Sacramento, six people tied to the R & R Wellness Collective dispensary were indicted in a case that has included allegations of hoarding more than $250,000 in cash and distributing marijuana to Southern California.

DeAngelo, whose Harborside Health Center dispensary is fighting a $2.4 million tax penalty by the Internal Revenue Service, complained that federal authorities are aiming their assaults at legitimate operators following state law.

"They have gone after the Marin Alliance, Northstone Organics and Harborside. These organizations are 100 percent compliant," he said. "They (federal authorities) should either learn how to aim or learn how to tell the truth."

Last week, state Attorney General Kamala Harris said in a statement that "ambiguities" in state medical marijuana law "must be resolved by the Legislature or the courts." Meanwhile, she warned that an "overly broad federal enforcement campaign will make it more difficult for legitimate patients" to obtain medical marijuana.

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