Montgomery County will appeal last month’s Circuit Court ruling that it violated Maryland election law by using public money to campaign for a 2012 ballot proposition that eliminated certain collective bargaining rights for police, officials said Thursday.

Circuit Court Judge Ronald B. Rubin ruled March 19 that County Executive Isiah Leggett (D) and public information director Patrick Lacefield improperly led an overtly political effort to win support for Proposition B. The measure eliminated a provision of county law that allowed the police union to negotiate a range of management decisions that went beyond salary, benefits and working conditions.

Voters passed the proposal to limit the union’s negotiating power by nearly 60 percent to 40 percent in November 2012.

Leggett and Lacefield spent about $200,000 in county tax revenue on advertising to build support for Proposition B. The judge ruled that the officials were effectively acting as a campaign committee that should have filed contribution and spending reports as required by state law.

In explaining the decision to appeal, County Attorney Marc Hansen said the county had the right to vigorously communicate with voters on a key public policy issue. “I think this is an important legal principle, and we should get a final word on this,” he said. He estimated that the Court of Special Appeals, the state’s second-highest court, would render a decision in 18 to 24 months.

Rubin declined to hold Leggett and Lacefield liable for damages sought by the Fraternal Order of Police, which filed the lawsuit against the county. He said they had acted in good faith on advice from attorneys. But the judge also said the pro-Proposition B campaign went beyond informing the public about a policy issue and lapsed into electioneering.

“There is a world of difference between communications that inform, and communications that proselytize and try to influence the outcome of an election contest,” Rubin said.

Leggett, who initially said it was doubtful the county would appeal, did not return a call Thursday.

Marc Zifcak, immediate past president of FOP Lodge 35, said Leggett “wants to clear his name using taxpayer money.” The union is appealing Rubin’s decision not to hold Leggett and Lacefield financially liable in the case.

Doug Duncan, who is challenging Leggett’s bid for a third term as county executive in the June 24 Democratic primary, expressed surprise Thursday when told the county would appeal. “The judge could not have been clearer,” he said. “They violated state law and county law.”