A state appeals court upheld California's 12-year-old medical marijuana law Thursday, rejecting two counties' arguments that allowing patients to use the drug with their doctor's approval condones violations of federal narcotics laws.

The Fourth District Court of Appeal in San Diego dismissed challenges by San Diego and San Bernardino counties, which objected both to the 1996 marijuana initiative and to recent legislation requiring counties to issue identification cards to users of medical pot.

The cards protect their holders from arrest by state or local police for possessing small amounts of marijuana.

The U.S. Supreme Court has ruled that the federal government can enforce its drug laws, which ban marijuana use and cultivation, against patients and their suppliers in California and the 11 other states that have legalized medical marijuana under their own laws.

But in Thursday's ruling, the appeals court said states remain free to decide whether to punish drug users under their own laws.

"The (federal) law does not compel the states to impose criminal penalties for marijuana possession," said Justice Alex McDonald in the 3-0 ruling, which upheld a Superior Court judge's decision.

"The purpose of the (federal law) is to combat recreational drug use, not to regulate a state's medical practices."

Besides, McDonald said, the counties' only obligation under the California law is to process and hand out the ID cards, a requirement that poses no conflict with federal law.

State and local officers can't arrest marijuana users for violating the federal law, he said, and applications for the medical marijuana cards contain a warning that they provide no shield against federal authorities.

Although the state's decision to allow medical marijuana use "arguably undermines the goals" of the federal law, McDonald said, county governments are unaffected by any such conflicts and therefore have no right to sue to overturn the entire state law.

San Diego County's lawyer, Senior Deputy County Counsel Thomas Bunton, said county supervisors may decide by next week whether to appeal to the state Supreme Court. He said a future appeal to the U.S. Supreme Court is also possible.

"We think the court should have found that California's medical marijuana laws are pre-empted by the federal law," Bunton said. "We think (the ID card law) requires us to issue cards in support of conduct that violates federal law."

Advocacy groups that joined the state in defense of its law said the ruling shows that states are free to chart their own course on medical marijuana.

The decision "provides yet further confirmation that states need not march in lockstep with federal policy," said Adam Wolf, an American Civil Liberties Union lawyer representing the National Association for the Reform of Marijuana Laws.

He said the court issued "a stinging rebuke to the misguided attempt of a few rogue counties to undermine the will of California's voters and the well-being of thousands of sick and dying patients."

In a separate case Thursday, the Third District Court of Appeal in Sacramento became the second to declare unconstitutional a 2003 state law that limited the amount of marijuana a patient could possess for medical use and remain exempt from prosecution.

The ruling would leave those decisions up to local governments, or to local prosecutors and juries in counties that lacked an official standard. The law, part of the same legislation that established the state-approved identification cards, allowed patients to possess up to 8 ounces of dried marijuana, or up to six mature marijuana plants or 12 immature plants, unless a doctor had recommended greater amounts to meet the patient's needs.

The Third District Court ruled that the law conflicted with the 1996 medical marijuana initiative, Proposition 215, which set no numerical limits on the amount of marijuana a patient could possess.

An appeals court in Los Angeles reached the same conclusion in May, a ruling that Attorney General Jerry Brown's office has appealed to the state Supreme Court.