REVERE-Mayor Thomas Ambrosino hopes he can hold the line on city spending by leaving eight jobs in major city departments vacant instead of resorting to employee layoffs to cut costs.?Even with these reductions,” he warned City Councilors in a letter they will review at Monday night?s meeting, “I am not certain that layoffs can be avoided.”That guarded forecast about city spending over the next year reflects uncertainty regarding state aid to the city and rising municipal costs including health insurance.His letter suggests that leaving city jobs vacant following retirements could “save money and avoid layoffs.” But he warned that approach potentially means leaving three Fire Department jobs, three or four police jobs and one or two Publics Works department positions unfilled.Ambrosino has not seriously considered laying off city workers since the financial rough period of 2002 and 2003 when city spending dipped $1 million into the red.The resulting city layoffs were triggered by reductions in state assistance to the city. Gov. Deval Patrick and the Massachusetts House have proposed slightly increasing the state?s current allocation to Revere from $13 million to $13.1 million, not including school assistance money.But the governor and the Legislature are at odds over Patrick?s plan to include anticipated casino revenue into local aid calculations with state Rep. Robert DeLeo warning earlier this year, “We must look for efficiencies and savings before we ever look to new revenue sources.”The spending differences and their possible resolution will come into sharper focus when the Legislature later this month begins debating the state budget and Patrick?s casino plan.