U.S. Attorney General Eric Holder said Thursday that the Cleveland police department systematically engages in excessive use of force against civilians, and that a court-appointed monitor will now oversee implementation of reforms. (Reuters)

The Obama administration on Thursday issued a report accusing the Cleveland police department of using excessive and deadly force against citizens in violation of their constitutional rights, the latest development in a growing national debate over the fairness of local police tactics, especially in minority communities.

According to the Justice Department report, Cleveland police engaged in a “pattern or practice” of unnecessary force — including shooting residents, striking them in the head and spraying them with chemicals. The Justice Department and the city agreed to establish an independent monitor to oversee changes in the police department, including better training and supervision of officers. And the Justice Department urged Cleveland civic leaders to hold police accountable for their improper actions when necessary.

Attorney General Eric H. Holder Jr. traveled to Cleveland to announce the measures in person. He set them against the backdrop of the recent deaths of three African Americans at the hands of police, including last month’s fatal shooting of 12-year-old Tamir Rice in Cleveland. Holder’s announcement came a day after a New York grand jury declined to bring charges in the death of Eric Garner, a 43-year-old African American man who died in July after police placed him in an apparent chokehold during an arrest.

“In recent days, millions of people throughout the nation have come together — bound by grief and anguish — in response to the tragic deaths of Michael Brown in Ferguson, Missouri, and Eric Garner in New York City,” Holder said at a news conference. “The tragic losses of these and far too many other Americans . . . have raised urgent national questions. And they have sparked an important conversation about the sense of trust that must exist between law enforcement and the communities they serve and protect.’’

Holder spoke amid growing public anger over the decision that no criminal charges will be filed against the officer in the Garner case — on the heels of another grand jury’s decision not to charge white Ferguson police officer Darren Wilson in Brown’s death. Both decisions triggered nationwide protests.

From the halls of Congress to the streets of New York City, demonstrators, Democratic politicians and some prominent conservatives called for a rethinking of police and prosecutorial tactics and firmer guidelines in determining when officers can use deadly force against citizens.

“The way we go about policing has to change,” New York City Mayor Bill de Blasio said as he announced a wholesale retraining of more than 20,000 officers, including a three-day course in how to handle confrontations on the street. “People need to know that black lives and brown lives matter as much as white lives,” added de Blasio, who campaigned in part on reforming police tactics that he said had unfairly targeted minorities.

Protests over the criminal-justice response to the deaths of Garner, Brown and others continued in downtown Washington on Thursday, with several hundred demonstrators gathered in front of the Justice Department. There were also protests in Boston, Chicago and New York.

The department said this week it will investigate Garner’s death, and it is probing Brown’s killing.

The escalating developments reflect a decades-old history of tension between police and the communities they serve, especially those in minority areas, experts in policing said. Nearly a half-century after the Kerner Commission investigating the devastating urban riots of the 1960s warned that the nation “is moving toward two societies, one black, one white — separate and unequal,” mistrust of law enforcement remains widespread in some communities, they said.

Law enforcement strategies that affect police-community relations can vary widely by state and locality, from the community policing model popularized in the 1980s and ’90s — in which officers walked the beat in neighborhoods and worked with local leaders — to the tougher, more intelligence-based approach that gained favor after the Sept. 11, 2001, attacks.

Tensions have exploded at times, such as during the 1992 Los Angeles riots that followed the acquittal of white police officers on trial over the videotaped beating of Rodney King, a black man. Five years later, New York City police beat and sodomized Haitian immigrant named Abner Louima with a broken-off broom handle, a case in which Loretta E. Lynch, now nominated to succeed Holder as attorney general, was the senior prosecutor.

Today, even though police-community relations “are a lot better than they were 20 years ago,” the recent police-involved killings revealed new fault lines, said David H. Harris, a law professor at the University of Pittsburgh and an expert on police practices. “If anyone thought we were out of that era in which some groups feel the law and policing are not applied equally to them, clearly we are not,’’ he said.

Much of the recent tension has been in New York City, where Rudolph W. Giuliani (R), as mayor in the 1990s, famously implemented what is known as the “broken windows” philosophy of policing. That approach involved zeroing in on small crimes, such as breaking windows or jumping subway turnstiles, to deter larger ones.

His successor, Michael R. Bloomberg (I), became known for “stop-and-frisk,” in which police stopped virtually anyone deemed suspicious, and crime rates fell for years in the city, as they have nationwide. A federal judge ruled last year that the policy discriminated against blacks and Hispanics, and de Blasio has embraced changes, touting statistics showing that stop-and-frisks are substantially down this year.

But Garner died after a confrontation with police over the unlawful sale of individual cigarettes, the kind of minor offense that has been the focus of the department’s approach for years. “We’re dealing with a kind of continuing legacy of the Giuliani and Bloomberg years,’’ said Harris, who added that the eight-year officer who put Garner in an apparent chokehold, Daniel Pantaleo, probably based his actions on “the standards and training he learned” when he joined the force.

The Justice Department report released in Cleveland on Thursday cited a series of examples of what the department called “unreasonable and unnecessary” use of police force. In one incident, the report said, 13 Cleveland police officers fired 137 shots at a car, killing both of its occupants.

In another, it said, an officer used a stun gun on “a suicidal, deaf man who committed no crime, posed minimal risk to officers and may not have understood officers’ commands.”

Officers were also accused of repeatedly punching a handcuffed 13-year-old boy in the face. He was already under arrest for shoplifting.

“Accountability and legitimacy are essential for communities to trust their police departments and for there to be genuine collaboration between police and the citizens they serve,” said Holder, who voiced optimism that “meaningful change is possible” in Cleveland.

He said the department’s Civil Rights Division has opened in the past five years more than 20 similar investigations into police departments nationwide, more than twice as many as were begun in the half-decade before that.

Alice Crites contributed to this report.