NEW ORLEANS — A federal judge has approved a sweeping agreement between the Justice Department and the city of New Orleans designed to clean up the city’s long-troubled Police Department, but Mayor Mitch Landrieu, who once strongly backed it, said the city wants to put the brakes on it because of costs.

Landrieu said he asked US District Judge Susie Morgan to delay final approval, largely because the Justice Department has also entered into a potentially expensive separate agreement with the New Orleans sheriff for overhauling the city-funded jail.