D.C. Attorney General Irvin B. Nathan testified against the referendum before the council and then the D.C. Board of Elections. It passed with 83 percent of the vote in an April 2013 special election. (Sarah L. Voisin/The Washington Post)

The team of activists who devised an unusual new strategy for gaining the District government more fiscal freedom from Congress say they always knew they were in for a fight. What surprised them, they say, is who their main adversary turned out to be.

The battle for D.C. budget autonomy — in short, the freedom of the city government to spend its locally raised taxes and fees without a congressional appropriation — now lies in the hands of a federal judge. To get there, the D.C. Council didn’t sue Congress or the president or any other arm of a federal government typically viewed as the District’s oppressor.

Rather, the council is suing agents of its own government, Mayor Vincent C. Gray and Chief Financial Officer Jeffrey S. De­Witt, who have both said they will refuse to abide by a recent amendment to the city charter calling for the government to direct its own spending. The amendment was approved by voters in a referendum last year.

Gray and DeWitt are following the advice of Irvin B. Nathan, the District’s attorney general. That it is the city’s top lawyer putting up the most significant roadblocks to progress, and not Congress or federal officials, deeply rankles the circle of lawyers and advocates who have seen the charter amendment as a way to put the city’s fight for greater freedom in its own residents’ hands.

“This new budget autonomy law is the biggest advance in D.C. democracy we’ve seen since 1973,” said Kimberly Perry, executive director of D.C. Vote, a prominent voting rights group. “There hasn’t been a win like this in 40 years we can celebrate. . . . Congress did not act to overturn this new law. Why would our own attorney general?”

On several occasions, Nathan has said he regrets being the “skunk at the garden party” objecting to the amendment. But his office has opined that the amendment is too clever by half, amending the 1973 home rule charter in a way that its drafters never intended.

“It has to be done in a lawful way,” he said in an interview. “If it is done in an unlawful way, it will have terrible consequences down the road.”

Among them, he has said, are the possibilities that city contracts could be challenged, city officials could be prosecuted for violating federal spending laws, and the implementation of the charter amendment could trigger a return of the federal financial control board that oversaw city government affairs from 1995 to 2000.

Those admonitions are a particular source of frustration to advocates.

“From where I sit, but for Irv Nathan’s opposition to this, this would all be behind us,” said Walter Smith, executive director of D.C. Appleseed, the think tank that helped develop the legal basis for the new strategy. “We would have budget autonomy in the city. Instead, we’re in the midst of a lawsuit.”

The idea for the referendum was first floated to Gray in the early days of his mayoralty, shortly after he was arrested alongside dozens of others who protested a Capitol Hill budget deal that newly imposed restrictions on the city’s funding of abortions for poor residents. At the time, there seemed to be little chance of getting Congress to loosen its reins on the District.

A novel legal strategy offered a solution: Use the charter’s own amendment process, in which the D.C. Council votes to put an amendment on a citywide ballot and voters ratify it, to allow the city to spend local funds without overt congressional approval.

Gray was “wildly enthusiastic,” said Smith, who suggested the strategy to Gray in 2011. But with a top House Republican, Rep. Darrell Issa (Calif.), expressing support for legislation, there seemed to be a chance for progress through normal channels, and the strategy was shelved.

By the time the D.C. Council moved forward with the charter amendment in 2012, Nathan and his deputies had determined that the strategy was so patently illegal that it could not be defended against potential lawsuits.

Nathan testified against the referendum before the council and later to the D.C. Board of Elections, which had to vote to put the matter on the ballot. It did so over Nathan’s objections, and in an April 2013 special election, voters approved it with 83 percent of the vote. Congress did not move to overturn the amendment during a subsequent review period, and the new charter language took effect Jan. 1.

Since then, the Government Accountability Office has rendered a non­binding legal opinion on the charter amendment, calling it “without legal force and effect,” echoing language in opinions issued by Nathan’s office.

The council has marshaled legal experts, including partners from two prominent firms working pro bono, to defend the charter amendment in court.

David A. Super, a Georgetown University law professor who has studied the budget autonomy proposal, said he finds Nathan’s warnings “completely implausible.” The charter amendment, he said, is eminently defensible in the courts.

“The D.C. Council’s on very solid footing here,” he said. “They’ve clearly got the better argument.”

Nathan, a former general counsel to the U.S. House, said his job is not to be a cheerleader for a political strategy, even one with admirable ends.

“I don’t accept the whole premise that it’s worth trying unlawful acts,” he said. “It’s fine for individuals like Martin Luther King or Gandhi to engage in civil disobedience when they take the consequences of their actions. . . . It’s quite another when they are exposing thousands of other individuals to sanctions and penalties and adverse consequences. In my opinion, there is no tolerance for a person who is sworn to uphold the law to violate the law.”

His posture has become a rallying point for advocates. D.C. Vote sent out a fundraising appeal last month calling Nathan’s position “an affront to DC voters and our goal of self-determination.” The appeal accused his office of having “aligned its legal analysis . . . with that of House Republicans.”

The case is now before U.S. District Judge Emmet G. Sullivan, who will hear arguments May 14 and issue a ruling shortly thereafter. The question in the minds of advocates is, what will Nathan do then?

If Sullivan rules in the council’s favor and Nathan takes the case to a federal appeals court, “I would wonder at that point whose interests we’re serving,” said D.C. Council Chairman Phil Mendelson (D).

Nathan said it was “premature” to say what he might do in those circumstances. But he noted that Sullivan made comments this week anticipating an appeal.

“I think it would be helpful to have a resolution by the Court of Appeals here,” he said. “That’s a higher court . . . and whatever that court decides will be accepted by all parties.”