A "giant mess" is how Los Angeles City Councilman José Huizar sees the conundrum over the expansion of medical marijuana, which is seen across the city in the growing number of patients with prescriptions, dispensaries popping up faster than Starbucks shops, and neighborhood complaints about rising crime and traffic.

The root of the "mess"? The challenge of carrying out the will of Californians, who in 1996 voted to decriminalize marijuana sales and possession for medicinal use, even as the federal government still deems marijuana, "medical" or not, to be an illegal drug, he says.

Such is the case in 15 other states that allow medical marijuana, leaving their local governments to sort out for themselves whether to encourage an above-board marijuana industry, as Oakland, Calif., has done, to fight it tooth and nail on grounds it's illegal under federal law, or to otherwise regulate it. Whatever they decide, it carries the risk of being in trouble with either state officials or federal authorities.

It's been a wild ride for L.A. Two years ago, the city council voted to allow dispensaries and then watched them proliferate to more than 800. As neighborhood residents complained about perceived jumps in crime, the council last year moved to restrict the outlets. Now it's not clear if the city even has that authority: A federal judge ruled in November (in a case from neighboring Long Beach) that marijuana is a drug subject to federal, not local, regulation.

California's law, says Mr. Huizar, "doesn't allow for local governments to regulate the ill effects of having marijuana so easily available. We've been trying to establish a balance between those who need it legally for medical reasons, and yet not be too easy for others who just want it to get high."

In the 15 years since California became the first state to adopt a medical marijuana law, the nation's general drift has been toward greater tolerance of marijuana use. Under President Obama, the Justice Department steered US prosecutors away from charging "individuals whose actions are in clear and unambiguous compliance with existing state laws providing for the medical use of marijuana" – though many say that no longer is the case.

Some say that Obama policy contributed to the current confusion, with the Feds missing in action as a patchwork of state laws and local rules sprang up around medical marijuana – much as has happened with illegal immigration. Lately, the Justice Department has moved to clamp down on marijuana dispensaries and growers, especially in California, citing large-scale criminal activity. Since October, for instance, federal agents have closed almost two-thirds of the 222 medical marijuana outlets in San Diego.

Mr. Obama "made it sound like he was going to take a different tack than his predecessor – that they are not going to go after patients but only large collectives," says Robert Mikos, a law professor at Vanderbilt University in Nashville, Tenn. "The simplified media sound bites made it look like they weren't going to enforce the ban, and when they did, marijuana advocates overdramatized it."

Most recently, the governors of three medical marijuana states – Washington, Rhode Island, and Vermont – petitioned the US government to reclassify marijuana as a drug with accepted medical uses, claiming the reclassification is needed so their states can regulate its safe distribution without risking federal prosecution.

Attorney General Eric Holder sought to clarify the US position during Dec. 8 testimony on Capitol Hill. But his carefully measured words may not have drawn the bright line that either backers or opponents of medical marijuana had hoped for. "Given the limited resources that we have, and if there are states that have medical marijuana provisions ... if in fact people are not using the policy decision that we have made to use marijuana in a way that's not consistent with the state statute, we will not use our limited resources in that way," Mr. Holder said.

Competing federal and state interests lie behind the emerging pot wars. Washington is concerned about international trafficking and relations with drug-producing countries, and states are responsive to constituencies who see benefits in medical marijuana, analysts say.

"Given that there is no clear, definitive set of policies at state, local, and national levels, politicians are picking and choosing whatever suits their local political and economic situations," says Matthew Hale, a political scientist at Seton Hall University in South Orange, N.J.

To Marta Irvington, the Feds' apparently reinvigorated stance against medical marijuana is disconcerting.

"This is 'Reefer Madness' all over again, edition 2011," says the single mom, referring to the 1936 hysteria film (and unintended cult hit of the subsequent hippie generation) that asserted cannabis use would lead children to lives of violence and disorientation resulting in rape, insanity, and suicide. "I'm legal, I've got a doctor's prescription, and yet I feel I have to slink around in the shadows because some federal narc is going to nab me ... or shut this place down," says Ms. Irvington, standing outside a dispensary in Sherman Oaks, Calif., after buying an ounce of marijuana to relieve back pain.

At least 70 percent of Americans support legalizing medical marijuana, polls show. The 16 states that now allow it account for roughly one-third of the US populace, and it is now available in more than 1,000 dispensaries.

Still, use or cultivation of the plant is strictly illegal under federal law – and courts have ruled that US law supersedes state law on this issue.

The crackdown has been multipronged, aimed at dispensaries and landlords who rent them retail space. In a New York Times op-ed on Nov. 6, Ethan Nadelmann of the Drug Policy Alliance complained, moreover, that the Treasury Department has forced banks to close accounts of medical marijuana businesses operating legally under state law. He urged Obama to "reassert" his original hands-off policy for those in compliance with state laws.

Some see politics as a motive for the crackdown, noting Obama will not want to run for reelection in 2012 as a full-fledged marijuana industry explodes on his watch. Others suggest that the pot industry may have overreached: Federal agents became concerned about industrial-scale cultivation and distribution operations that would attract criminal gangs and, possibly, terrorist networks, they say.

Still others say the horse is out of the barn – and probably can't be put back.

"Federal raids and prosecutions might convince some dispensary operators to close," says Alex Kreit at the Thomas Jefferson School of Law in San Diego. "But many more [dispensaries] are willing to continue operating and take the legal risk, particularly those that are run by true believers."