After months of heated debate, the St. Paul Police Federation and the city of St. Paul have turned to arbitration in hopes of reaching an agreement on a new police contract.

Officials for the police union and the city met Tuesday with an arbitrator from the state Bureau of Mediation Services to start the process, federation President Dave Titus said. A decision isn’t expected for months, he said.

The city has offered the union a 5.5 percent increase over three years. But the union has pushed Mayor Chris Coleman for more, arguing that a greater increase would make the department competitive in salary with other metro agencies.

The union says the city’s police department ranks 22nd out of 27 metro departments in average annual salary based on 30-year career comparisons. The mayor’s office has argued that the department is in the top five metro jurisdictions when total compensation, including benefits, is taken into account, a position the union disputes.

Union employees continue to work under terms of a contract that expired in 2012.