The detective’s union is the latest city union to hash out an early tentative contract with the city, Mayor Bloomberg announced yesterday.

The proposed deal — reached six months ahead of deadline— would guarantee regular raises for detectives until 2012 that would total 20%. It would also raise the base pay of first-grade detectives to six figures and allow first-grade detectives with 20 years on the job to make more than $118,000.

The early deal with the Detectives Endowment Association is part of a Bloomberg administration effort to avoid red-eye negotiating over contracts and long arbitration battles.

Mr. Bloomberg said the early deals made it easier for the city to plan its finances, and he brushed aside a question about whether escalating salaries could force the city to raise taxes to cover the costs. “I hope we do not have to raise taxes,” he said.

The detectives union president, Michael Palladino, said the deal would give his members financial security after decades of late contracts.

“The money was there. It was on the table,” he said. “There was no reason not to go after it.”

The detectives’ deal stirred up bad blood between the largest police union, the Patrolman’s Benevolent Association, and the city, which are locked in state arbitration proceedings over that union’s overdue contract.

The mayor said he was ready to restart negotiations any time the PBA decided to come back to the table, to which the union president, Patrick Lynch, said he would be happy to do so if the city offered more money.