Mr. Chaffetz, a spirited defender of states’ rights, said he saw the issue differently from those supporting the will of local government. “Washington, D.C., is not a state,” he said, adding, “I just don’t think that Washington, D.C., should be a haven for smoking pot.”

While Washington is often out front on progressive policy initiatives, it is not the leader on marijuana. Colorado, Washington State, Oregon and Alaska have passed laws legalizing its recreational use, and more than 20 states allow marijuana use for medical purposes. This city, like many states, has also decriminalized possession of low amounts of the drug, treating it as a civil infraction. The legalization measure imposed a two-ounce limit for personal use — similar to that in other states, but less than Oregon’s eight-ounce limit.

The District of Columbia law does not permit retail sales, but allows home cultivation.

“That’s important,” said Robert Mikos, a law professor at Vanderbilt University and an expert on drug laws. “That is consistent with conservative norms because it is about privacy and autonomy over your own house. But it is important to recognize that it is hard to control home cultivation.”

Further, while some Republicans have argued that the district measure runs afoul of federal drug laws, states are not required under the Constitution to enforce those laws, which is the basis of state decriminalization statutes.

Even if Washington goes forward with its new law, Congress has other means for peeling it back. Through policy riders, it has stopped a needle-exchange program intended to limit the spread of AIDS among heroin users and prevented the district from using its own money to help fund abortions for poor women, among other things.

“This is a rare victory, and it may be a temporary one,” Ms. Norton said of the discovery of the loophole.

Or, there is always a lawsuit to file.

“My guess is if the Council tries to move forward that some district resident who opposed marijuana legalization will sue and the federal courts will then decide,” said Garry Young, the director of the George Washington Institute of Public Policy.