The report, and a pledge by city officials to reform the police department, come in the last days of the Obama administration, which has aggressively pursued investigations of abuse by local law enforcement.

On Friday, Chicago leaders said they had promised to negotiate with the federal government an order, enforceable by a judge, that would reform how the police department handles training, accountability and the way officers use force. A similar agreement is in place for the city of Baltimore.

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But President-elect Donald Trump’s nominee for attorney general, Jeff Sessions, has criticized government lawsuits that force police reforms. And Trump himself has been a staunch defender of police officers, who he has called the “most mistreated people in this country,” and he has said that crime in this country is on the rise and requires a forceful response.

When asked whether the Chicago action would retain its strength under a Trump administration, Attorney General Loretta Lynch said Friday she expected the agreement with Chicago to live on beyond Obama’s term.

“Yes, the top people at the Department of Justice move on, but this agreement is not dependent on one, or two, or three people,” she said.

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The report details a grim succession of anecdotes.

Officers are described as running after people who they had no reason to believe committed serious crimes. Some of those chases ended in fatal gunfire. In one case, officers began chasing a man who was described as “fidgeting with his waistband.” Police fired a total of 45 rounds at him, hitting and killing him. No gun was found on the man, the report states, and a gun found almost a block away was both “fully-loaded and inoperable.”

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These anecdotes were not limited to fatal incidents. A 16-year-old girl is described as being struck with a baton and shocked with a Taser for not leaving school when she was found carrying a cellphone. A 12-year-old Latino boy was “forcibly handcuffed” without explanation while riding his bike near his father.

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Federal officials were also told about officers taking young people to the neighborhood of a rival gang to either leave them there “or display the youth,” putting their lives in danger by suggesting they had given information to police.

While the federal officials on Friday noted that city officials have made efforts recently to enact reforms, they said “complicated and entrenched” causes of the problems could only be fixed with outside help.

The report is the culmination of a 13-month investigation into the country’s second-biggest local law enforcement agency, which has a grim history that includes a former police commander who spent decades leading a torture ring until he was suspended and then fired in the early 1990s.

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During the news conference on Friday, Chicago Police Superintendent Eddie Johnson said “some of the findings in the report are difficult to read.” But he also said that many of the problems had already been identified and officials were working to correct them.

“Quite simply, as a department, we need to do better, and you have my promise, and commitment, that we will do better,” Johnson said.

Officers are described as lying, as part of a “code of silence” and also in cases where they had little reason to lie, the report states.

But investigators also described an utter absence of morale in the police force, as officers increasingly feel they are adrift and unsupported, and the report describes suicides and suicide threats among officers as “a significant problem.”

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Many “officers feel abandoned by the public and often by their own department,” the report states. “We found profoundly low morale nearly every place we went within CPD. Officers generally feel that they are insufficiently trained and supported to do their work effectively.”

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Dean C. Angelo Sr., president of the Chicago Fraternal Order of Police, did not respond to a message seeking comment Friday.

The Justice Department began its Chicago investigation in December 2015, just weeks after authorities in the city released video footage showing an officer fatally shooting Laquan McDonald, a black 17-year-old.

This dashboard-camera recording, withheld for more than a year by city officials, showed Officer Jason Van Dyke firing 16 shots into McDonald, some after the teenager had already crumpled to the ground, despite initial accounts that the teenager had lunged at the officer. The video unleashed a torrent of anger on the streets of Chicago, which became the latest in a series of cities that boiled over in recent years after a fatal encounter involving police.

The recording has continued to reverberate in the city. Not long after it was made public, the Justice Department announced that it would begin what is known as a “pattern or practice investigation” into the police department. Mayor Rahm Emanuel (D), facing intense criticism, ousted Garry F. McCarthy as police superintendent, while voters decisively dismissed Anita Alvarez, the prosecutor in the case, in an election that highlighted the McDonald shooting.

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Emanuel also created a task force to review how the Chicago police handled accountability, training and oversight, and the group released a highly critical report last year, describing the McDonald video as a tipping point giving “voice to long-simmering anger.”

In what some viewed as a prelude to the Justice Department’s findings, the task force’s report described repeatedly hearing from people who felt some police officers are racist and said the police force’s own data “gives validity to the widely held belief the police have no regard for the sanctity of life when it comes to people of color.”

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McCarthy, Johnson’s predecessor, had criticized the Justice Department before the report was released and said investigators never contacted him. Asked about that on Friday, Lynch said that investigators had tried but he was “unavailable,” although she did not elaborate.

Reached after the news conference, McCarthy declined to discuss the contents of the report — saying he still had to review it with his lawyer — but disputed that Justice Department investigators attempted to reach him.

“That is a lie,” McCarthy said. “With all the investigative resources of the federal government, they couldn’t find me here, in River North, which is a neighborhood in Chicago. That is absurd.”

The American Civil Liberties Union of Illinois said that the findings confirmed “what we have known for decades” about policing in Chicago.

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“The Chicago Urban League believes that the report must be viewed as a milestone,” Shari Runner, president and chief executive of the group, said in a statement. “It is verification of the worst of what we’ve been and continue to be, but offers a viable path to what we want to become.”

Distrust remains an issue between police officers and residents in Chicago. In a poll taken last year, one in three residents said the city’s police officers were doing an excellent or good job; far fewer black residents (12 percent) felt that way then white residents (47 percent) or Hispanic residents (37 percent). The new report also states that police use force almost 10 times as often against black people as white people. Complaints filed against officers by white people were substantially more likely to be substantiated than those filed by black people or Latinos.

Federal investigators said their inquiry found that Chicago police force did not provide officers with suitable guidance for using force, investigate improper uses of force or hold officers accountable for such incidents. Investigators also faulted the city’s methods of handling officer discipline, saying the process “lacks integrity,” while saying that in the rare case where misconduct complaints are sustained, discipline is “haphazard and unpredictable.”

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Training is repeatedly described as woefully inadequate, with the report describing officers in a class on deadly force being shown a video made more than three decades ago that depicted tactics “clearly out of date.”

Emanuel acknowledged Friday that there were questions were surrounding what the next administration would do, but vowed to continue working with the government.

“We will continue on the path of reform, because that is the path of progress,” he said. Emanuel later added, “We’re going to continue to work with that new Justice Department.”

Speaking on Capitol Hill during his confirmation hearing this week, Sessions suggested that entire departments filled with good officers could be tarred by the work of individuals and was critical of lawsuits that force reforms.

“These lawsuits undermine the respect for police officers and create an impression that the entire department is not doing their work consistent with fidelity to law and fairness, and we need to be careful before we do that,” Sessions said. He would not commit to leaving unchanged agreements that are in place when he takes over, though he said he would enforce them until changes are made.

The Justice Department can investigate and force systemic changes­ on local police departments and sue them if they do not comply. This authority was given to the federal agency in 1994, when Congress acted in the wake of the 1991 beating of Rodney King by Los Angeles police officers and subsequent unrest following the acquittal of the officers involved.

During the Obama administration, the Civil Rights Division has opened 25 investigations into law enforcement agencies, according to the Justice Department. Probes have found patterns of excessive force used in police departments including Portland, Ore., Cleveland, Albuquerque, New Orleans, Seattle and Puerto Rico, among others.

The Chicago probe was among the the largest pattern and practices investigations in the Justice Department’s history, involving a force that has 12,000 officers, trailing only the New York police force among local law enforcement agencies in the United States.

The announcement in Chicago came the same day that Justice Department officials also said that the Philadelphia Police Department was making “tremendous progress” in implementing findings from an assessment last year examining how officers use deadly force there.

A day before Lynch spoke in Chicago, she had traveled to Baltimore for officials to outline efforts to revamp policing there. Baltimore’s agreement on reforms came after the Justice Department released, last year, a blistering report accusing the city of discriminatory policies targeting black residents.

Angelo, the head of Chicago’s police union, has said he was concerned federal investigators were rushing to finish the probe before Trump’s inauguration. When asked Friday about the timing of the report’s release, Lynch noted the investigation had begun more than a year ago, though she acknowledged lawyers had worked “quickly” to bring it to fruition.

“This is not a political process, this is an investigative process,” Lynch said.

This story has been updated since it was first published at 9:06 a.m.