Adam Eidinger, center, chairman of the DC Cannabis Campaign, and other protesters march through Washington, demanding that Congress remove an appropriations rider that would overturn a popular ballot initiative legalizingmarijuana. (Sarah L. Voisin/The Washington Post)

D.C. officials and activists for marijuana legalization launched a long-shot bid Wednesday to halt a federal budget deal that appeared poised to upend the city’s successful ballot measure last month to legalize the drug.

The day after Congress came to a tentative budget deal that included language intended to block the city’s measure, proponents chanted and marched to Capitol Hill, held a sit-in at the office of Senate Majority Leader Harry M. Reid (D-Nev.) and promised to keep urging congressional leaders to let the District govern itself.

(Related: Five reasons why D.C. may still declare pot legal)

“The best thing that could happen here — the only good thing — is that people around the country may finally realize that the will of people in D.C.” is not respected, said D.C. Council member David Grosso (I-At Large), a leading advocate for legalization.

“Members of Congress of both parties are willing to sell us down the river to get some of their priorities through,” Grosso said. “Hopefully, people will stand up this time and say, ‘Enough is enough.’ ”

View Graphic The status of marijuana laws across the nation.

In recent weeks, for a rare moment, D.C. voters found themselves on the leading edge of a liberal social-policy experiment. A voter-backed measure to legalize marijuana passed overwhelmingly last month, bringing a debate about drug policy that had simmered in faraway Western states to the nation’s capital.

Then Congress stepped in. With the simplest of policy orders — a few sentences tucked into a 1,600-page spending bill — negotiators all but invalidated the will of D.C. voters.

Although the spending bill remained in flux late Wednesday, the language affecting the city’s marijuana initiative was not expected to change. Congress could vote on the budget as soon as this week.

It was not the first time federal lawmakers had meddled, but blocking Initiative 71 became the latest and perhaps most visible example of the city’s lack of autonomy.

On Nov. 4, voters in Alaska, the District and Oregon chose to legalize marijuana, but only the District’s vote was subject to interference by Congress, which not only determines the city’s federal spending allotments but is also empowered to restrict even how local tax dollars are used to enact and enforce laws.

The provision added to the $1 trillion spending bill prohibits the District from using any of its own funds or federal funds to enact or implement drug laws that are weaker than federal ones, which still classify marijuana in the most dangerous class.

Just how powerless D.C. lawmakers and activists remain to turn back the affront to local autonomy was repeatedly evident Wednesday.

From left, Adam Eidinger, Dr. Malik Burnett and Michael Brown leave the office of Senate Majority Leader Harry Reid, after staging a sit-down protest over the overturning of the city’s recently passed law legalizing marijuana. (Bill O'Leary/The Washington Post)

Reid never bothered to return to his office to meet with protesters assembled there. The group left after two hours. Outside, the legalization advocates were vastly outnumbered by crowds protesting perceived mistreatment by police in Ferguson, Mo., and New York.

House Minority Leader Nancy Pelosi (D-Calif.) issued a statement demanding that the two “worst” Republican-crafted provisions be struck from the spending bill, a measure that would keep the government open until next fall, but neither had to do with the District or its marijuana measure.

Even the District’s nonvoting member of the House of Representatives, Del. Eleanor Holmes Norton (D), was left waiting to plead with colleagues about the measure Wednesday night when a committee instead recessed for a floor vote.

In interviews, Norton, D.C. Mayor Vincent C. Gray (D) and several members of the D.C. Council acknowledged that although the spending measure remained in turmoil, the city had zero leverage to remove the passage blocking the city’s marijuana initiative.

With Republicans set to take control of the chamber in January, the defeat suggested that the will of D.C. voters may be suspended indefinitely.

“We don’t know that there’s anything else for us to do,” Gray said.

Norton and a cadre of allies, however, pinned hopes on a misreading of the bill, saying that by one interpretation, the congressional provision couldn’t stop an initiative already passed by voters.

D.C. election officials formally certified the referendum result Dec. 3, and the D.C. Council has yet to send the measure to Congress for the legislative review period. Norton said she did not believe that “ministerial” act would be prohibited by the so-called congressional spending rider.

And she said she did not believe that the District needs to pass additional laws or write regulations to implement the initiative should it pass the review period.

“The bill already passed does not require any regulations,” she said. “It has everything in it.”

Republicans maintained forcefully that the intent of the budget language was clear and that District’s marijuana measure would be rendered ineffective once the bill is voted on.

“It has to go through all the final steps, which have not yet been taken,” said Rep. Andy Harris (R-Md.), who first proposed the language to halt the measure.

“The takeaway is that if Congress passes this amendment, it will have taken the position that it is way too early to proceed with legalization in the District of Columbia, and I think that most people think we should wait for more scientific evidence from states that have attempted legalization,” Harris said.

The final determination for the city will be made by the D.C. attorney general. A spokesman for the office said attorneys were still reviewing the matter and were not prepared to comment. The D.C. Council’s chief attorney also said he was still reviewing the measure.

On Wednesday, however, city attorneys said they were increasingly confident that the budget deal would not be able to roll back a law passed by the D.C. Council and signed by Gray in the spring to join 18 states that have eliminated criminal penalties for marijuana possession.

The District now issues a $25 citation for marijuana possession.

Last month, Mayor-elect Muriel E. Bowser (D) said she would not implement the legalization initiative without a companion plan to tax and regulate pot sales because it could lead to open-air drug markets. But she backed off that stance Wednesday. She suggested that she may be willing to try to implement Initiative 71, as Norton believes is possible, without a system for legal sales, which the congressional measure would clearly prohibit.

“My job is to uphold the will of the voters, and the voters overwhelmingly support legalizing marijuana in the District,” Bowser said, adding that a half-measure would still be problematic. “I continue to think that public safety is best served by having clear and enforceable laws.”

Gray on Wednesday renewed his calls for the city to be granted more freedom from congressional control — a yoke that was loosened in recent years under a Democratic Senate but now appears to be tightening.

“We are pretty good about being able to endure tracks over the top of us from the buses running over us,” Gray said. “This is just another example of walking on the District of Columbia’s rights. We’ve got citizens who have spoken on this issue. We’ve got other states that have spoken on this issue, and the District of Columbia is the only entity that is being subjected to this.”

Mariam Baksh contributed to this report.