WASHINGTON – Medical marijuana users will get a long-awaited day in the nation’s second-highest federal court next week, when California-based activists argue for looser regulations.

While voters in Washington and two other Western states are preparing to vote on legalizing recreational pot use, the California activists hope to redefine how the federal government classifies the drug. The case, years in the making, could turn federal law enforcement on its head.

“It’s symbolic, and it’s extremely important,” Kris Hermes, spokesman for Americans for Safe Access, said Friday, “and it will force the federal government to rethink how it addresses this issue.”

The drug regulation dispute will be taken up Tuesday by a three-judge panel of the U.S. Court of Appeals for the District of Columbia Circuit, which is influential because it oversees many federal agency decisions. The half-hour oral argument, pitting Americans for Safe Access against the Obama administration’s Justice Department, is the latest step in a drug regulation case begun a decade ago.

Based in Oakland, Calif., home for the nation’s medical marijuana movement, Americans for Safe Access is challenging the Drug Enforcement Administration’s continued classification of marijuana as a Schedule I drug. Schedule I drugs, which also include the likes of heroin, are officially deemed to have a high potential for abuse and no currently accepted medical use.

The DEA last year upheld the agency’s strict marijuana classification following extended review, and the Justice Department argues the appellate court need not second-guess this decision.

“There was no available evidence of adequate, well-controlled studies demonstrating marijuana’s safety and effectiveness as a medicine and no consensus among experts as to these issues,” Justice Department attorneys Lena Watkins and Anita J. Gay advised the appellate court in a legal brief. “The enactment of state laws allowing the use of marijuana for medical purposes did not constitute the required science-based evidence.”

Watkins and Gay further cited the “extensive illicit domestic and international trafficking of marijuana as evidence of the widespread use and abuse” of the drug.

An estimated 16.7 million U.S. residents currently use marijuana, according to the most recent federal surveys. Among 12th-graders, an estimated one in five had used pot within the past month, according to a 2010 survey.

The first crucial test is whether the medical marijuana advocates have the standing, or legal right, to file the lawsuit in the first place. The Justice Department argues the advocates can’t show they suffered the kind of harm needed to bring a case.

If the judges agree, they can dismiss the challenge and avoid the trickier question of whether the DEA acted “arbitrarily and capriciously” in rejecting the original 2002 petition seeking reclassification of marijuana. It took five years for the Department of Health and Human Services to complete its evaluation and recommendations, and another four years for the DEA to issue its decision.

Advocates say regulators ignored several hundred peer-reviewed studies on the efficacy of medical marijuana, as well as the medical marijuana laws passed by Alaska, California, Washington and 13 other states.

“They just blew it on the science,” Americans for Safe Access attorney Joseph D. Elford said Friday.

The appellate court will probably not rule on removing marijuana from the restrictive Schedule I status. It could, however, order the DEA to take a more in-depth look at the available evidence.