The Administration for Children’s Services will hire 100 new investigators with law enforcement backgrounds to help transform what a scathing study released yesterday by city investigators described as the agency’s culture of complacency, neglect, and dishonesty.

The 141-page report by the Department of Investigation commissioned by the mayor exhaustively details the bungled cases of 11 children who died and one who nearly drowned while their families were being monitored by the agency. Among the deaths were the high-profile murders of 7-year-old Nixzmary Brown and 4-year-old Quachaun Browne.

The report found a pattern of incompetence and negligence up the line from caseworkers to the agency’s management, including cases closed “where unstable, potentially deadly situations remained unresolved in the homes” and caseworkers who lied to cover up their own inaction when children died.

“These 10 cases revealed a road map of problems with ACS investigations — the same problems that this city has seen over and over again in the past,” the commissioner of the City of New York Department of Investigation, Rose Gill Hearn, who led the 18-month study, said. “Facts were not ascertained and children were left at risk because ACS did not have all of the information.”

The report detailed instances of caseworkers routinely accepting the denials of parents accused of abusing their children, without bothering to check with other witnesses.

“DOI’s investigation has revealed grave problems in the quality and integrity of the investigations conducted by ACS staff,” the report said. “ACS staff often conducted careless, incomplete investigations of serious abuse allegations.”

Caseworkers also frequently neglected to check up on families where abuse had been found, didn’t bother to obtain critical medical records or criminal background checks, and dragged their feet in seeking legal action when they were barred access to hostile homes.

In one instance, the case of Quachaun Browne, who died after he was beaten repeatedly over the course of a weekend by his mother’s boyfriend, was closed even after an ACS worker found that the home was filthy and empty of food after responding to reports that the children were eating garbage and begging from neighbors.

In another, a caseworker didn’t investigate discrepancies in the accounts of Nixzmary Brown’s siblings about injuries she had that appeared to be the result of abuse. Instead, the caseworker accepted Nixzmary’s stepfather’s account that Nixzmary had fallen on a piece of wood. Her emaciated body was found a month later after her stepfather was accused of banging her head against a faucet and sexually abusing her.

Meanwhile, caseworkers were often working without cars, cell phones, or even notebooks to record interviews, and were provided only limited training in the techniques of investigation and interrogation.

Ms. Gill Hearn suggested that to fix its many failings, the agency’s priority should be to “get the facts.” She recommended the hiring of 100 “investigative consultants” with law enforcement experience that will cost the city about $3 million.

Twenty investigators were hired this year as a part of reforms the agency has been implementing since the uproar over the death of Nixzmary Brown, which have included the firing or discipline of 14 workers. With the additions, Ms. Gill Hearn said there would be one investigator to every 15 caseworkers.

Ms. Gill Hearn proposed 25 other recommendations, including encouraging caseworkers to travel in pairs instead of alone, and teaching them to take notes.

She also said the agency should learn from past reform efforts that led to only nominal, superficial changes.

The ACS commissioner, John Mattingly, called the study a “very tough report.”

“In child protection, there is no quick fix, no silver bullet,” he said. “This is not going to be a snap your fingers and put out a new policy and everything will be better.”

But he also said he was appreciative of the report and planned to implement the recommendations.

He added that ACS is making progress despite challenges, including a dramatic increase in reports of child abuse since Nixzmary’s case in 2006, to an estimated 61,000 this year from 48,000 in 2005.

This year, he said in 40% of cases, workers had documented evidence of abuse, up from 33% in 2005. By increasing the number of caseworkers to about 1,300 from 900, Mr. Mattingly said the average caseload has fallen to 11 this year from 20 in 2005, although some caseworkers still have up to 20 cases at a time.

“We have a ways to go,” he said. “But we have seen improvements.”