WASHINGTON — Police across the United States are rethinking how they use force amid national outrage over questionable shootings and violent arrests.

The changes include efforts in Dallas to train officers to de-escalate situations by moving backward during target practice and arming some with sponge projectiles, perhaps as early as June. In Camden, New Jersey, officers are taught about the sanctity of life and encouraged to take time to defuse a situation, even if a suspect is wildly waving a knife at them.

San Antonio’s police chief, William McManus, said his department is overhauling the training of officers on de-escalation tactics to be broader and more in-depth.

“The takeaway from all this is that we need to re-engineer the use of force. We need to look at our practices, look at our training,” he said Monday. “We need to teach de-escalation. We need to teach time and space and communication in spaces like that.”

McManus was in Washington on Friday, one of nearly 200 law enforcement leaders from across the nation who gathered to discuss new guiding principles for the estimated 18,000 law enforcement agencies in the United States.

The 30 principles include an unprecedented acknowledgment from leading law enforcement professionals that officers should go beyond the Supreme Court-adopted basic legal standard that asks what a “reasonable officer” would do in such a situation and that officers should focus on preserving all human lives in any encounter.

“There’s an expression, ‘Lawful but awful,’” said Chuck Wexler, executive director of the Police Executive Research Forum, who led the effort to develop the principles. “I think (these principles) would impact on some level these really tragic shootings of the mentally ill, the homeless person, the unarmed person. It could have an enormous impact.”

The principles, to be released in an upcoming report, require officers to respond proportionally to a suspect, imagining the public’s perception of that response. They also require officers to communicate effectively instead of, for example, repeatedly telling a suspect to drop the weapon.

The principles also recommend departments stop training on “outdated concepts,” such as the “21-foot-rule,” which refers to the distance a suspect armed with a knife can close before an officer can draw a weapon. Instead, officers are encouraged to create distance and use cover to give themselves more time to respond.

McManus said SAPD would review each of the group’s recommendations and determine how to implement them.

When McManus recently returned to run SAPD for a second stint, he said one of his top priorities would be to push the department in further policing reform.

SAPD has made significant headway in policing and mental illness. The San Antonio department has a mental-health unit, which in September was featured on an ABC News segment about policing.

Los Angeles Police Protective League Director Jamie McBride, a detective who is one of nine representing LAPD’s 9,800 sworn officers, said the new principles weren’t new and were common sense. He also noted that officers patrol communities that are often heavily armed and violent.

“It’s always been about preservation of life. That goes to both sides — the police and the suspect,” McBride said. “We’ve always learned to try to communicate. We’ve always tried to de-escalate. We know all this stuff. Unfortunately, we don’t live in a perfect world.”

Express-News Staff Writer Josh Baugh contributed to this report.