SAN FRANCISCO – A new Obama administration policy loosening guidelines on federal prosecution of medical marijuana on Monday signaled to users that they had less to fear from federal agents but still left their suppliers to contend with a tangled mesh of state laws and regulations.

The Justice Department told federal prosecutors that targeting people who use or provide medical marijuana in strict compliance with state laws was not a good use of their time.

Marijuana advocates and patients called the memo an encouraging step forward from the strict anti-pot policies of the Bush administration. But many worried that the web of laws in the 14 states that allow medical marijuana use could still leave medical marijuana providers vulnerable to prosecution.

"Now we've got to figure out what these words actually mean," said Wayne Justmann, a longtime pro-pot activist in San Francisco who campaigned for the 1996 ballot measure that made California the first state to legalize medical marijuana.

The state stands out for the inconsistent enforcement of medical marijuana laws. There are as many as 800 storefront pot shops in Los Angeles just as some dispensary owners are starting decades-long sentences in federal prison. Some cities are trying to clamp down on medical marijuana, while others offer permits and collect taxes on dispensaries just like any other small business.

The confusion makes some medical marijuana backers skeptical that anyone can feel secure they are clearly in compliance with state law and safe from federal prosecution.

"There's just too much disagreement about what the law is," said Dale Gieringer, director of the California chapter of The National Organization for the Reform of Marijuana Laws. "The legality of almost anything is in doubt in California when it comes to dispensaries."

On Monday, for example, a state judge temporarily barred Los Angeles from enforcing a ban on medical marijuana clinics, ruling that the City Council failed to follow state law.

California also stands alone for the widespread presence of storefront dispensaries, but places to legally obtain pot are starting to sprout in other states. Colorado also has dispensaries, and Rhode Island and New Mexico are in the process of licensing providers.

Marijuana is effective in treating chronic pain and nausea, among other ailments, advocates say. In the past, federal agents have focused on busting dispensaries they said were using medical marijuana as a front for traditional drug-dealing and earning millions in the process. The Justice Department's latest memo suggests that approach will continue.

"We will not tolerate drug traffickers who hide behind claims of compliance with state law to mask activities that are clearly illegal," Attorney General Eric Holder said in a statement.

The Justice Department memo emphasizes that prosecutors have wide discretion in choosing which cases to pursue. In particular, the memo urges prosecutors to pursue marijuana cases which involve violence, the illegal use of firearms, selling pot to minors, money laundering or involvement in other crimes.

The states that allow some use of marijuana for medical purposes are Alaska, California, Colorado, Hawaii, Maine, Maryland, Michigan, Montana, Nevada, New Mexico, Oregon, Rhode Island, Vermont and Washington, by the government's count.

But who exactly determines what compliance at the state level means is still a contentious question. California, for example, does not have an agency similar to its department of Alcoholic Beverage Control that focuses on marijuana. As a result, it has been up to the courts, city governments and local law enforcement to determine who is following the state law and who is not.

On Oct. 9, attorneys for the city of Fresno, Calif., obtained a restraining order to force the closure of nine pot clubs for violating zoning laws that require them to comply with both state and federal laws, an essentially impossible requirement since the U.S. government classifies pot as an illegal narcotic.

Assistant City Attorney Doug Sloan said the Justice memo would not inhibit Fresno's ongoing effort to keep out medical marijuana dispensaries.

"The memo expressly says this doesn't legalize marijuana," Sloan said. "Until federal law changes, and right now marijuana is a Class 1 controlled substance, it will still be prohibited."

In Colorado, where voters allowed the use of small amounts of marijuana for medical reasons, there are no statewide rules regulating the increasing numbers of dispensaries and cities have taken to regulating them on their own. For the new federal policy to have any effect, lawmakers need to create the regulations, Colorado Attorney General John Suthers said.

Patrons at a dispensary in San Francisco said they hoped the new policy would lift the stigma surrounding pot.

But they refused to give their names, saying they would not trust the federal government until marijuana was made completely legal.

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Associated Press writers Greg Risling in Los Angeles, Tim Korte in Albuquerque and Devlin Barrett in Washington contributed to this report.