A fully budded marijuana plant ready for trimming is seen at a marijuana store in Colorado. A marijuana decriminalization law passed by the D.C. Council in the spring takes effect this week. (RICK WILKING/REUTERS)

On Wednesday, a D.C. police officer who caught someone carrying a small amount of marijuana was required to launch his suspect on an onerous journey through the criminal justice system — possibly involving handcuffs, fingerprinting and forensic analysis.

On Thursday, that same officer faces the simpler task of pulling out a ticket book and checking a box: littering, or possession of marijuana?

A lengthy civic debate over how to handle the most minor of drug offenses culminated at midnight Wednesday when a marijuana decriminalization law passed by the D.C. Council this spring completed a 60-day congressional review period and took effect.

(Quiz: How much do you know about D.C.'s marijuana law?)

The advent of the new law, spurred by reports of stark racial disparities in marijuana arrests, prompts a sea change in how police handle one of the most common violations they encounter. Under new orders set to take effect Thursday, police can no longer take action upon simply smelling the odor of marijuana. Nor can they demand that a person found in possession of up to 1 ounce produce identification.

Those found with larger amounts or caught using marijuana in public places can still be arrested and charged with a crime. Otherwise, officers who catch someone carrying weed will be required simply to confiscate any visible contraband and write a ticket carrying a $25 fine.

Street officers will probably be uneasy with the changes, said Delroy Burton, chairman of the D.C. police union, even though the department has circulated a lengthy special order and created a PowerPoint presentation on how to make arrests.

Burton criticized the new law as too vague and confusing to officers on the street, and he said those who must enforce it had little input into its creation.

“This is not a simple issue,” he said. “It’s about enforcement and decriminalization and where you draw the line of what officers can do and cannot do. Our officers are going to have to go out there and enforce a convoluted mess.”

D.C. Police Chief Cathy L. Lanier has said previously that she does not believe the new law will affect officers clearing street corners or confronting suspicious people.

In a statement, police spokeswoman Gwendolyn Crump sought to combat a misconception among District residents that possession and use of marijuana have been legalized. “This is absolutely not true,” the statement said.

The department has prepared wallet-size cards laying out key facts about the law, and information will also be posted starting Thursday at www.mpdc.dc.gov/marijuana.

D.C.'s new marijuana law took effect July 17. How much do you know about the District's new law? Take the quiz.

Among the vagaries of decriminalization is that federal law enforcement agencies — such as the U.S. Park Police, Secret Service and Capitol Police — may still arrest anyone carrying any amount of marijuana under federal drug statutes. Those offenses would be presented to the U.S. Attorney’s Office in the District for prosecution.

D.C. police, who have historically made the vast majority of marijuana arrests, will abide by the new law. Civil violations will be adjudicated by the city’s Office of Administrative Hearings, while misdemeanor crimes such as smoking marijuana in public will be prosecuted by the D.C. attorney general. More serious felony drug crimes will remain in the hands of federal prosecutors.

Burton said the most confusing part of the new rules relates to when an officer may search or arrest someone on a marijuana charge.

The new order says that the odor of marijuana does not constitute a “reasonable articulable suspicion” that the law has been violated. An officer must have evidence that a person has more than 1 ounce of the drug. And an officer cannot assume a person has a larger amount just because he or she is holding “multiple containers” of the drug.

But the order says that none of those restrictions apply to car stops when police are “investigating whether a person is operating or in physical control of a vehicle” while intoxicated or impaired by drugs.

Burton said these rules create an almost impossible burden on how an officer approaches and investigates a suspected drug violation. He said the law seems to prohibit an officer from investigating an odor during a car stop for speeding or running a red light. To be safe, he said, officers “are probably going to ignore” possible drug infractions.

Under the law, the odor of marijuana coming from a vehicle can prompt an officer to investigate whether the driver is operating while impaired, but not whether the driver or others in the vehicle are in possession of marijuana.

“We understand changes in the law can be confusing, which is why we have an online training that includes potential scenarios and examples for members.,” said Crump, the department’s chief spokeswoman. “It is an ongoing process, and we will continue to put forward additional training and scenarios as new questions arise. Officers know that in every situation, they need to consider the totality of the circumstances.”

D.C. police said the department has shared its officer-training materials with prosecutors and the D.C. Housing Authority. That training, the department said, is required for any officer making a marijuana arrest starting Thursday.

Civil violation notices that police already hand out for littering have been amended to include possession of marijuana and note the $25 fine. Possession of 1 ounce of the drug will cost a miscreant less than the fine for throwing a cigarette butt on the ground — $75 for littering.

Under the new order, an officer is allowed to issue only a warning if he or she “feels it to be in best interest of justice.”

The long-term prospects for the city’s marijuana laws remain unsettled. Congressional Republicans have sought to intervene, adding language meant to overturn the law to a spending bill that is expected to pass the House on Wednesday. But Democrats are unlikely to go along in budget negotiations, which in any case could be months down the road.

Meanwhile, advocates for the legalization of marijuana are seeking to have D.C. residents vote on the question in November — and, according to recent polling, their initiative is likely to be successful should it qualify for the ballot.