The District’s lengthy struggle to spend locally raised tax dollars without congressional approval came to an end Jan. 1, when a widely supported voter referendum took legal effect.

Or did it?

The practical effect is still in question, as it remains to be seen how two key players — Congress and the District’s new chief financial officer — will respond to the April vote, whose legitimacy was doubted by even some high-ranking city officials, including Mayor Vincent C. Gray and Attorney General Irvin B. Nathan.

The budget autonomy measure — which, among other things, would exempt local government functions from future federal government shutdowns — is not likely to have an immediate effect on the city’s operations. The Capitol Hill deal that ended the October federal shutdown granted the city freedom to spend its budget through the end of its fiscal year, on Sept. 30, rendering the matter moot for the time being.

But the Government Accountability Office is undertaking a high-stakes review of the matter, which could guide how both a key congressional committee and new finance chief Jeffrey S. DeWitt approach the matter as city leaders begin developing the 2015 budget.

The review was ordered by the House appropriations subcommittee overseeing the District’s budget, and staff for the GAO, the investigative arm of Congress, have solicited opinions from local authorities, including Nathan and the D.C. Council, in recent months. A report is set to be issued later this month, GAO spokesman Chuck Young said Thursday.

At issue is whether the referendum process was a permissible method to amend the District’s charter as it deals with budgetary issues. Backers of the referendum argued that a public vote was in fact a valid tactic, while Nathan argued that only an act of Congress could make such changes.

The GAO’s determination could guide how key members of Congress approach the referendum — particularly House Republicans, who adopted a skeptical stance in a July committee report, calling the vote an “expression of the opinion of the residents, only, and without any authority to change or alter the existing relationship between Federal appropriations and the District.”

The referendum passed in an April 23 special election, with 83 percent of voters supporting it.

Jennifer Hing, a spokeswoman for the appropriations committee, declined in September to release the panel’s formal request for the GAO opinion. She did not respond to a request for further comment made Friday.

Absent congressional action, the most important player is DeWitt, who assumed the city’s top financial post Friday and has independent control of the city’s fiscal apparatus. He could determine that the referendum is not legally binding and refuse to implement it.

DeWitt’s predecessor, Natwar M. Gandhi, asked Nathan in an August letter to provide guidance on the referendum.

Neither man’s office would provide a copy of Nathan’s reply, but two people familiar with the response but not authorized to comment publicly on it said it contained objections largely the same as those Nathan lodged to the Board of Elections last year. Among Nathan’s objections has been that city officials could be exposed to prosecution should they expend public funds appropriated under a faulty referendum.

Ted Gest, a spokesman for Nathan, declined to comment, citing the confidentiality of the office’s legal advice.

David Umansky, a spokesman for DeWitt, said lawyers in the finance office continue to review the matter and are waiting for Nathan and the GAO to weigh in further.

The referendum’s backers, meanwhile, are undertaking efforts to make sure their efforts are not derailed — either on Capitol Hill or, more alarmingly in their view, in the John A. Wilson Building.

Kimberly Perry, executive director of D.C. Vote, an advocacy group for voting rights that played a leading role in the referendum push, said city officials are “obligated to implement the law.”

“We plan to work with them and make sure they’re accountable to D.C. voters,” she said. “It would be disappointing if somehow the new law were undermined by our own officials and elected leaders, but we don’t anticipate that happening. Nobody wants to undermine democracy.”

Even a GAO opinion questioning the referendum’s validity, backers said, would not change the law’s effect.

Walter Smith, the executive director of D.C. Appleseed, a policy group that helped develop the referendum strategy, said he believes Congress passed on chances to reject the measure — first, during a review period following the public vote, then during the fall’s budget negotiations.

“Once Congress has reviewed the referendum, the GAO ought not to be opining on it,” Smith said. “The only thing that now can stop this is a court order or a congressional enactment.”

But D.C. Council Chairman Phil Mendelson, who strongly backed the referendum and helped secure the council’s unanimous support, said it would be much better if the review finds the referendum was valid.

“If the GAO concludes that the charter could be amended, I believe everybody will fall into line,” he said. But if it concludes otherwise, “it is complicated. . . . It would still have to be resolved.”