Legal experts said it marked the first time in decades that a federal district court judge seriously considered marijuana's classification. Judges have generally accepted the classification and the federal ban on its use, growth and distribution.

Mueller's decision was expected, but her move to hold a hearing last year to consider the issue marked a significant step that reflects growing skepticism about federal marijuana law, said Sam Kamin, a marijuana regulation expert at the University of Denver Sturm College of Law.

"While this one came out the other way, what you see is a lot of momentum in changing federal marijuana law," he said.

Mueller said during a 15-minute court hearing that she was initially prepared to grant the defense motion, but then decided from the facts of this particular case that "this is not the court and this is not the time." She said she decided it was up to Congress to change the law if it wishes.

She said a written ruling would be issued by the end of the week.

"It has been 45 years since Congress passed the Controlled Substances Act," she said, noting that "the landscape has changed" since then.

However, while the courts are an independent branch of government, they are not designed to act as a maker of public policy, she said.

Defense attorney Bill Bonham, speaking for his fellow attorneys, said he was disappointed.

"I felt that the judge was leaning to grant the motion, from our previous hearings, so I guess it's disappointing," he said.

Mueller gave the defense attorneys three weeks to regroup before a May 6 court hearing to set a trial late this year or early next year in the case.

Attorneys for the nine defendants in the case had argued that marijuana was far less harmful than legal drugs, and its classification as a Schedule 1 drug was arbitrary in violation of the Constitution. They also said the government enforced marijuana laws unevenly, allowing its distribution in states that have legalized it while cracking down elsewhere.

Prosecutors said marijuana met all the criteria for a Schedule 1 drug, saying it has no accepted medical use and a high potential for abuse. They also argued that Mueller did not have jurisdiction to consider how marijuana was classified.

The criminal complaint filed in 2011 named 16 defendants and accused them of conspiring to grow at least 1,000 pot plants as part of an operation that included land in Shasta-Trinity National Forest in California.