“THE DISTRICT has learned the hard way that expenditures must be based on available resources and not based on hopes for future windfalls.”

That stern warning came as the D.C. Council began discussing next year’s proposed budget, but it wasn’t delivered by the office that traditionally has ridden herd on the free-spending impulse of elected officials. In fact, the city’s new chief financial officer was among those on the receiving end of D.C. Council Chairman Phil Mendelson’s (D) apt lecture on responsible budgeting. That represents a surprising and troubling turnabout.

Jeffrey S. DeWitt, who in January replaced Natwar M. Gandhi as the District’s independent chief financial officer, signed off on a fiscal 2015 spending plan proposed by Mayor Vincent C. Gray (D). As several council members pointed out at an April 7 hearing, that plan rests on some questionable assumptions — including that, as The Post’s Aaron C. Davis reported, more money would be spent next year than the city expects to take in.

Mr. Gray proposed initiatives in education, workplace development and other areas. To help pay for the programs, the lame-duck mayor proposed carrying over windfall funds from fiscal 2014 to fiscal 2015. And what about 2016, when Mr. Gray will be out of office but the programs will continue to cost money? The ostensible solution is to find money by improving efficiency and eliminating waste elsewhere in the government.

Administration officials estimate savings of 8 percent in non-personnel services through cost-cutting initiatives. We are all for streamlined government, but it’s premature, foolish even, to depend on savings that have yet to be realized. That’s especially true when much of the windfall is supposed to come from procurement reform, maximizing Medicaid reimbursements, reducing homelessness and other reforms that are not exactly new ideas but have been stubbornly difficult to implement.

If the assumptions prove faulty, the spending could prove to be a “time bomb,” Mr. Mendelson warned. Mr. DeWitt told the council that the city would have plenty of time to make adjustments to balance the budget if more revenue or other savings did not materialize. He assured us that he would keep a close eye on spending to ensure a balanced budget and that he is confident, based on reforms he helped bring about in his previous job in Phoenix, that savings can be realized. He said he sees his job as offering choices to the mayor and council.

We hope that Mr. DeWitt also realizes that part of his job is saying no. One reason the District’s finances are in such enviable shape is that his predecessors, notably Mr. Gandhi and Anthony A. Williams, blew the whistle when politicians wanted to spend money they didn’t yet have.