WASHINGTON — Attorney General William P. Barr warned that communities and critics of policing must display more deference or risk losing protection, a stark admonition that underscored the Trump administration’s support for law enforcement amid an ongoing national conversation about police brutality against minorities.

“They have to start showing, more than they do, the respect and support that law enforcement deserves,” Mr. Barr said on Tuesday afternoon in comments at an awards ceremony for policing. “And if communities don’t give that support and respect, they may find themselves without the police protection they need.”

The speech immediately sparked criticisms that Mr. Barr was conflating protests of police misconduct with a disrespect for the police and that he was advocating lawlessness as a potential reprisal.

“The idea that the attorney general of the United States, the nation’s chief law enforcement officer, is recommending abandoning communities as retribution for pushing for police reform or criticizing policing practices, is profoundly dangerous and irresponsible,” said Vanita Gupta, the president and chief executive of the Leadership Conference on Civil and Human Rights and the former head of the Justice Department’s civil rights division.