WASHINGTON (AP) — A police group's proposal that law enforcement officers be required to do more than what's minimally required by law in violent encounters has spurred anger and pushback from leading national groups representing chiefs and rank-and-file sworn officers.

The Police Executive Research Forum, a Washington-based think tank, last week unveiled its 30 new principles that re-envision how officers use force after national outrage over questionable shootings and violent arrests initially sparked by the fatal shooting of 18-year-old Michael Brown in Ferguson, Missouri, police in 2014. Since then, incidents from New York to Texas — often caught on bystander or police camera — have resulted in soul-searching among officers as a wary public recoils from the violence that's sometimes inherent in policing and frequently permitted by law.

The police research group's recommendations include an unprecedented acknowledgement by police professionals that officers should go beyond the Supreme Court-adopted basic legal standard that asks what a reasonable officer would do in such situations, and encourage officers to focus on preserving all lives, not just their own.

Two of the most influential police groups, the International Association of Chiefs of Police and Fraternal Order of Police, said they have problems with the proposals.

Setting different policies and standards would lead to confusion and hesitation by police, endangering officers and the public, the police chiefs' group said. It emailed its 19,000 members in the United States this week to say it was "extremely concerned" about the recommendations.

The group's president, Police Chief Terry Cunningham of Wellesley, Massachusetts, said such a proposal needs more research and involvement from police, plus a recognition that officers are under scrutiny and asked to deal with social issues on the streets, such as mental illness.

"Using force is an unfortunate part of the job," Cunningham said. He said police are confronting people responsible for murders. "Usually those are really dangerous people, clearly, and those are people usually the police have to deal with and bring them into custody."

The Police Executive Research Forum, or PERF, developed its proposals after about 18 months of research. Law enforcement officials even went to Scotland to observe Scottish officers, who are nearly all unarmed, back away from suspects with their hands up, for example, to defuse situations without violence.

"We don't believe that we should just move headlong based on PERF having taken a trip to Scotland, that we should just turn policing in a country, God knows how many times bigger than Scotland, totally on its head," said Jim Pasco, executive director of The Fraternal Order of Police, which represents 335,000 sworn officers.

He added: "We're not going to stand by and let police officers be sacrificed on the altar of political correctness."

PERF's executive director, Chuck Wexler, said the Supreme Court case was the "floor" and not the "ceiling" and that law enforcement officers need to do better.

"We aspire to have a higher standard in terms of preventing these unfortunate situations from happening at all. That's what this is about," Wexler said. "This is about the difference between legal versus moral."

The 1989 Supreme Court ruling, Graham v. Connor, by which officers are judged in court notes that an officer makes split-second decisions and relies only on what police know in the moment of decision about whether to use force.

For years it was rare for a chief to determine that an officer had violated department policy if the officer met that legal standard. In recent years, departments from Los Angeles to Milwaukee have more frequently disciplined officers for violating its force policy even if no charges were filed.

But such varying standards leave a police department open to civil liability and claims. Training — and adhering to it — becomes more critical, said retired Los Angeles Police Department Sgt. Lou Salseda, an expert and former police academy instructor.

"You can write any policy you want, but if you don't train your officers, what happens (is officers say:) 'That's what they wrote, but I never got training,' or 'the last time I got training was three years ago,'" Salseda said.

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Follow Tami Abdollah on Twitter at http://www.twitter.com/latams.

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Online:

PERF's recommendations: http://tinyurl.com/god86rn

Police Foundation infographic: http://tinyurl.com/j9mtody