The de Blasio administration covered up its failure to screen child-welfare workers for criminal convictions — endangering “the health and safety” of kids in its care, state officials charged.

The head of the state Office of Children and Family Services said she’s “deeply troubled” over the assault of a 6-year-old boy allegedly by a convicted murderer who was working for the agency — which exposed the city Administration for Children’s Services’ failure to conduct mandatory criminal background checks, according to an Aug. 17 letter obtained by The Post.

“By failing to comply with the requirements to process criminal background checks . . . ACS has compromised the health and safety of the vulnerable children [under its care],” Acting OCFS Commissioner Sheila Poole wrote in a scathing letter to ACS Commissioner David Hansell.

The state launched an investigation after the Aug. 3 incident, but Poole accused ACS of dragging its feet in providing records.

She said the documents that had been provided make it clear “ACS abdicated its responsibility” of screening job applicants through the state’s Justice Center for the Protection of People with Special Needs as required by law.

She also said files examined by her office show many ACS workers weren’t checked against an “exclusion list” of people with histories of abuse or neglect, and that checks conducted by the city’s Department of Citywide Administrative Services excluded the FBI’s database.

DCAS spokeswoman Jacqueline Gold said her agency always checks the FBI database.

“We forward fingerprints of proposed job candidates to the NYS Division of Criminal Justice Services, which checks with both the State of New York and the FBI. DCAS receives results from both entities,” she said.

ACS came under renewed scrutiny when counselor Jacques Edwards allegedly slammed a 6-year-old boy into a filing cabinet at a Manhattan youth shelter, and it was later learned that Edwards served time for murder.

A law enacted in June 2013 requires ACS to check the criminal history of any job applicant who will have contact with children through the Justice Center.

But soon after the law took effect, ACS began ignoring it.

Poole said that while ACS started conducting proper checks in August 2017, it never went back to “address the issue retrospectively” and weed out potentially dangerous staffers as it promised.

That left “hundreds of staff caring for children, and allowed others to have contact with such children, without conducting the required background checks to determine whether they posed a risk to the children in care,” she wrote.

She further found that ACS hasn’t been conducting another background check through the Statewide Central Register of Child Abuse and Maltreatment as required by a 1980 law.

The situation was so worrisome that Poole ordered ACS to “rectify this situation immediately.”

ACS insists that it opened all its files to the state, changed its policies and that Edwards, the convicted killer, would never get hired today.

“We take this very seriously, as the safety of the children in our care is always our top priority. We launched a review two weeks ago, as soon as we learned about this, and that review is well underway. We put in place stronger background check processes last year, which reflect our higher standard when working with children; this person would not pass our vetting process today,” said ACS spokeswoman Marisa Kaufman.

OCFS said it stands by Poole’s letter and its findings.