WASHINGTON — When President Richard Nixon signed the Controlled Substances Act in 1970, the federal government put marijuana in the category of the nation’s most dangerous drugs, along with LSD, heroin and mescaline.

In legal parlance, pot is a Schedule 1 drug, with a high potential for abuse and no medical purpose.

Forty-six years later, the law might soon change, as the Obama administration prepares to make what could be its biggest decision yet on marijuana.

Suspense is mounting after the U.S. Drug Enforcement Administration missed its self-imposed June 30 deadline to decide whether to reschedule the drug and recognize its potential therapeutic value. Twenty-six states already have legalized its medical use.

For Christine Gregoire, the former Democratic governor of Washington, a decision has been a long time coming.

In 2011, she and Republican Lincoln Chafee, who was then the governor of Rhode Island, filed a 106-page petition with the DEA, arguing that the categorization of marijuana was “fundamentally wrong and should be changed.”

In an interview, Gregoire said she “naively had such high expectations” that the DEA would act long before now, but she predicted the agency will approve the rescheduling.

“To be honest with you, I’d be shocked if they didn’t,” Gregoire said. “Frankly, in five years the entire world has changed in Washington state. Today we have recreational marijuana, and the Justice Department’s nowhere to be found.”

Voters in Washington and Colorado became the first in the nation to legalize recreational marijuana in 2012, a year after the governors filed their petition.

With the Obama administration adopting a policy to “just look the other way” in states with recreational marijuana, Gregoire said it would be hard for the DEA to justify keeping marijuana on the Schedule 1 list.

Opinions differ on what exactly might happen when the DEA responds to the petition, but a move to reschedule marijuana would be a major milestone in the decades-long push to legalize pot.

Among other things, it could pave the way for pharmacies to fill marijuana prescriptions and allow universities and others to conduct more medical research.

Many pot entrepreneurs hope that Congress would respond by helping marijuana businesses, allowing them to deduct their expenses from their federal taxes and giving them access to banks so they can phase out their all-cash operations.

Some predict that rescheduling could even make it easier for marijuana users to challenge policies that allow employers to fire them for positive drug tests.

Allen St. Pierre, executive director of the National Organization for the Reform of Marijuana Laws, said the DEA’s decision would be “remarkably consequential,” adding: “It will really cast the direction one way or the other.”

To be sure, there are plenty of skeptics who doubt the DEA will change anything at all.

“I’ll believe it when I see it,” said Gregory Carter, medical director of St. Luke’s Rehabilitation Institute in Spokane, Washington, who helped write the petition.

The DEA has given no indication of how it might rule, and President Barack Obama has said that any decision to reschedule marijuana should be left to Congress.

Kevin Sabet, president of the anti-legalization group Smart Approaches to Marijuana, said the chances of the DEA rescheduling the drug were “close to zero,” adding that there’s no scientific basis for doing so.

“The effects would be almost purely symbolic, and legalizers would use the move to further obfuscate the facts,” Sabet said.

Even if marijuana gets demoted to Schedule 2, it would still be a highly controlled drug, in the same category as cocaine. And with marijuana still illegal under federal law, a decision to reschedule would leave pot businesses running in the same gray area they do now.

That would mean continued risk for anyone growing, selling or buying the drug in the four states — Washington, Colorado, Alaska and Oregon — that have legalized the drug and those that have approved its use for medical purposes.

The Obama administration decided to let the states sell marijuana as long as they do a good job of policing themselves, a policy that both major presidential candidates, Democrat Hillary Clinton and Republican Donald Trump, have said they’d follow.

Under pressure from members of Congress to reschedule marijuana, the DEA promised in April that a decision would come “in the first half of 2016.” DEA acting Administrator Chuck Rosenberg and two other top administration officials, Health and Human Services Secretary Sylvia Burwell and drug czar Michael Botticelli, made the promise in a letter to Democratic Sen. Elizabeth Warren of Massachusetts and other senators who have been pressing the issue. In the letter, administration officials said they had already consulted with the Food and Drug Administration, which would oversee any pharmaceutical sales of marijuana.

Many who use the drug as medicine and have come to rely on their local dispensaries fear that a move to reschedule the drug might allow big pharmaceutical companies to take over the industry.

“It’s kind of scary to think that you’re going to have to go to a pharmacy and purchase a pre-prepared compound that you don’t know if it’s going to work,” said Kari Boiter, 36, who uses medical marijuana to treat her Ehlers-Danlos syndrome, a genetic disorder that affects skin, joints and blood-vessel walls.

Boiter, the former Washington state coordinator for the pro-legalization group Americans for Safe Access and now a Montana resident, said she worried that pharmaceutical companies might not offer a wide variety of marijuana products, including the pot-infused lotions, salves and bath salts that she used.

“It’s not a one-size-fits-all approach. What works for my migraines doesn’t work for my nausea, doesn’t work for my joint pain,” she said.

In the long run, many say, the best solution is not to reschedule marijuana but to “deschedule” the drug, putting it in the same category as tobacco and alcohol.

In May, Rep. Denny Heck, D-Wash., joined 13 other House members in urging Obama to consider descheduling the drug in the last few months of his presidency, telling Obama he has “a rare opportunity to move the country forward.”

Last month, Heck complained when the House rejected his plan to ban federal regulators from penalizing banks that work with state-approved marijuana dispensaries, saying they’ve become inviting targets for thieves. He said his “worst fears were realized” in June, when a security guard was killed during an armed robbery at a marijuana dispensary in Aurora, Colo.

As the DEA prepares to act, the man in the hot seat is Rosenberg, who infuriated pot advocates last year by dismissing the idea that smoking marijuana has any medical value.

“We can have an intellectually honest debate about whether we should legalize something that is bad and dangerous, but don’t call it medicine. That is a joke,” he told reporters at a briefing.

But as more states vote to legalize medical or recreational marijuana, the issue is winning more support on Capitol Hill. Senators will debate the potential medical benefits and risks of marijuana Wednesday, when the Judiciary Subcommittee on Crime and Terrorism takes up the issue.

When Rosenberg appeared before the full Senate Judiciary Committee last month, North Carolina Republican Sen. Thom Tillis urged him to back his bill that would make it easier to research the medical effectiveness and safety of marijuana. Tillis said he was particularly interested in more study of cannabidiol, or CBD, a form of cannabis oil that has been shown to reduce seizures.

“I’ve said over and over if it turns out that we find something in that plant that helps kids with epilepsy, I promise you, I will be at the front of the parade, leading the band,” Rosenberg replied.

Whenever Rosenberg announces the decision on rescheduling, pot activists plan to gather in front of the White House for a “smoke-in,” either to celebrate or protest. They’ll assemble at 4:20 p.m., in honor of 420, the popular code for marijuana.

It might be a big day for Gregoire, who laughed at the notion of playing a role in getting marijuana off the list of Schedule 1 drugs and helping to change a Nixon-era law. “You know I grew up in those times. I remember those times, the ’60s,” she said.

She said she first saw the value of medical marijuana in the late 1970s, when her legal secretary was diagnosed with cancer and found help by using marijuana.

Gregoire said rescheduling the drug would allow safe access to medical marijuana for more patients in states where it had not been approved, while clearing the way for more much-needed research.

“That was my whole intent,” Gregoire said. “Let’s not knee-jerk react to some yesterday’s ’60s proclivity against marijuana.”