A large and respected association of physicians is calling on the federal government to ease its strict ban on marijuana as medicine and hasten research into the drug’s therapeutic uses.

The American College of Physicians, the nation’s largest organization of doctors of internal medicine, with 124,000 members, contends that the long and rancorous debate over marijuana legalization has obscured good science that has demonstrated the benefits and medicinal promise of cannabis.

In a 13-page position paper approved by the college’s governing board of regents and posted Thursday on the group’s website, the group calls on the government to drop marijuana from Schedule I, a classification it shares with illegal drugs such as heroin and LSD that are considered to have no medicinal value and a high likelihood of abuse.

The declaration could put new pressure on Washington lawmakers and government regulators who for decades have rejected attempts to reclassify marijuana.

Bush administration officials have aggressively rebuffed all attempts in Congress, the courts and among law enforcement organizations to legitimize medical marijuana.

Clinical researchers say the federal government has resisted full study of the potential medical benefits of cannabis, instead pouring money into looking at its negative effects.

A dozen states including California have legalized medical marijuana, but the federal prohibition has led to an enforcement tug of war.

In California, federal agents continue to raid cannabis dispensaries, and the small cadre of physicians specializing in writing cannabis recommendations so that people can use medical marijuana has come under regulatory scrutiny.

Given the conflicts, most mainstream doctors have steered clear of medical marijuana.

The American College of Physicians’ position paper calls for protection of both doctors and patients from criminal and civil penalties in states that have adopted medical-marijuana laws.

“We felt the time had come to speak up about this,” said Dr. David Dale, the group’s president. “We’d like to clear up the uncertainty and anxiety of patients and physicians over this drug.”

Medical-marijuana advocates embraced the position paper as a watershed event that could help turn the battle in their favor.

Bruce Mirken, a San Francisco spokesman for the Marijuana Policy Project, said the ACP position is “an earthquake that’s going to rattle the whole medical-marijuana debate.”

The group, he said, “pulverized the government’s two favorite myths about medical marijuana -- that it’s not supported by the medical community and that science hasn’t shown marijuana to have medical value.”

But officials at the White House Office of National Drug Control Policy said calls for legalizing medical marijuana were misguided.

“What this would do is drag us back to 14th century medicine,” said Bertha Madras, the agency’s deputy director for demand reduction. “It’s so arcane.”

She said guidance on marijuana as medicine ought to come from the U.S. Food and Drug Administration, which she said is unlikely ever to approve leafy cannabis as a prescription drug.

Two oral derivatives of marijuana’s psychoactive ingredient, THC, have won FDA approval, and the agency is also in the early stages of considering a marijuana spray.

An FDA spokeswoman declined to comment on the group’s position and referred inquiries to a 2006 media advisory noting that the agency has never approved of smoked marijuana as a medical treatment

In the 12 years since California voters approved the nation’s first-ever medical marijuana law, several medical organizations -- including the American Nurses Assn. and the American Public Health Assn. -- have urged Congress to make cannabis a legal medicine.

But the ACP is second in size only to the American Medical Assn., which has about 240,000 members.

The AMA has urged research into medical marijuana but opposes dropping it from Schedule I. Backers of the ACP’s position expressed hope that it could help nudge the AMA to adopt a similar stance.

“This could be a sea change,” said Dr. Abraham L. Halpern, a professor emeritus at New York Medical College.

Halpern said he intends to petition the AMA to endorse rescheduling marijuana and to push for changes in federal regulations that would prevent federal anti-drug agencies -- the U.S. Drug Enforcement Administration and the National Institute on Drug Abuse -- from having virtual veto power over cannabis research.

The ACP position paper urges the use of non-smoked forms of cannabis as well as further research to identify the illnesses best treated with cannabis and the proper dosages for specific conditions.

It called for further research into cannabis as a pain reliever for conditions such as rheumatoid arthritis and as an aid in treatment of neurological and movement disorders such as spasticity, pain and tremor in patients with multiple sclerosis, spinal-cord injuries and other trauma.

But it cast doubt on marijuana’s efficacy for treating epilepsy and intraocular pressure caused by glaucoma, conditions that cannabis specialists in California routinely recommend be treated with pot.

The biggest effect of the report could be symbolic.

With a presidential campaign under way, the ACP’s stand could gain traction on the campaign trail or in a new administration.

“It’s going to depend on how the wind is blowing -- how we the people are thinking and reacting, where we stand on this,” said Dr. Jocelyn Elders, U.S. surgeon general during the Clinton administration and a professor emeritus at the University of Arkansas School of Medicine.

“I think we’ve come a long way in the last decade or so.”

eric.bailey@latimes.com