Schools Chancellor Dennis Walcott’s refusal to testify under oath at a recent City Council hearing on the education budget came, sadly, as no surprise.

The Department of Education under Mayor Bloomberg has shown a tendency to play fast and loose with facts. To this administration, the truth changes at any given time to whatever spin the administration wants to put out to the public.

Take, for example, the mayor’s pronouncements about the city’s budget. Every year, the mayor paints the city as broke, without the money it needs to negotiate new and fair contracts with the UFT and other unions. And then, as the budget deadline approaches, billions of dollars miraculously appear.

Or consider Walcott’s testimony to the City Council in the middle of the school bus strike earlier this year. He said the DOE could not include job protections for experienced bus drivers and matrons in its bid for new contracts. “It would be illegal,” he testified.

But city lawyers in court papers filed later said something quite different. They conceded that the city could include seniority protections if it merely took the step of providing evidence of the public benefit of the protections.

That contradiction was on the minds of the Council’s Education Committee members on June 4 when they asked Walcott to take an oath before testifying.

After consulting city lawyers, Walcott declined to take an oath. He said later that he had been advised against it because of lawsuits to which the city is party.

It was an embarrassment for the city that one of our leading public officials could not vouch that he was telling the truth when testifying before the city’s elected legislative body.

But one good thing came out of it. Education Committee Chairman Robert Jackson announced that from now on everyone who testifies before the committee will be asked to take an oath.

Good. Our public leaders must tell the truth. As we have seen under the Bloomberg administration, you can’t build good public policy on lies.