PATERSON, NJ – The city promoted 13 firefighters on a “provisional” basis over the weekend, a move officials said would fill openings in the command structure created by retirements.

The fire department promotions come about six months after the city demoted 34 police lieutenants and sergeants to save money.

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Glenn Brown, the director who oversees Paterson’s fire and police departments, said the firefighter promotions actually were designed to save money as well.

After several dozen high-ranking firefighters retired earlier in the year, the fire department has been forced to pay overtime to other ranking officers to fill vacancies in the command structure, Brown said. Promoting the 13 officers will prove to be cheaper than paying the overtime, he said.

City Council President Anthony Davis and the city council’s finance chairman, Kenneth Morris, were unaware of the promotions.

“That better not be true,’’ said Davis. “”No one let us know about it.’’

The city has not released a list of the 13 promoted firefighters and their new salaries. Brown said making the promotions “provisional” will reduce the short-term costs. Under the fire department’s contract, Brown said, firefighters receiving “provisional” promotions are entitled smaller raises than those given new positions on an “acting” basis.

Privates were promoted to captain, captains to battalion chief and battalion chiefs to deputy chief, officials said. Eventually, the plan is to make the promotions permanent, Brown said.

Last fiscal year, when the city terminated 125 police officers, it did not make any cuts among its firefighters. Officials said that was mainly because a federal program that provided funding to hire firefighters would have imposed severe penalties that would have offset the savings from layoffs.