WASHINGTON - Philadelphia Police Commissioner Charles H. Ramsey on Tuesday launched the first of a series of wide-ranging hearings on police policy and community trust in his role as the head of a presidential task force aimed at addressing national concerns on policing.

The 11-member task force was cochaired by former University of Pennsylvania professor Laurie Robinson, and boasted a diverse slate of researchers, activists, and law enforcement officials.

"We have a great opportunity for change, significant change," Ramsey told attendees. "None of us would be here today if we did not believe it was possible."

For hours on Tuesday, the task force heard from criminal-justice experts, police union representatives, and community advocates who spoke about building trust between police departments and minority groups following the high-profile, police-involved killings last year that touched off nationwide protests.

Suggestions were at once wide-ranging and specific, with attendees proposing solutions as broad as a national commission to study the country's entire justice system and as simple as an initiative to encourage police officers to use more respectful language.

At times, the participants themselves highlighted the very gaps the task force hopes to bridge.

Police union representatives lamented what one called a "smear campaign" against officers in the aftermath of police-involved shootings.

Another panelist spoke of how the killing of Sean Bell - shot to death by New York police officers while celebrating his bachelor party in 2006 - had discouraged him from a dream of becoming a police officer.

That panelist, Jim St. Germain, who now runs a nonprofit that mentors at-risk youth, said: "Our communities want public safety, but we also appreciate civil liberties, and we do not believe that the two are mutually exclusive."

Still, attendees - from police officers to political activists - agreed that rebuilding communities' confidence in their police forces is paramount.

"It is the most important and critical issue in our lifetime," said panelist Charles Ogletree, a Harvard law professor and the director of the Charles Hamilton Institute for Race and Justice.

Ramsey was appointed to head the task force weeks after widespread protests following a grand jury's decision not to indict the Ferguson, Mo., police officer who in August shot and killed 18-year-old Michael Brown.

Days after his appointment, another wave of protests was touched off when a grand jury declined to indict a New York City police officer in the death of Eric Garner, who was killed in July after he was apparently placed in a choke hold.

In both cases the officers were white, and the men who died were unarmed African Americans.

Philadelphia's own policing policies were highlighted during Tuesday's testimony, as Mayor Nutter joined mayors from Sacramento, Calif., and Baltimore for a round of questions. He cited dramatic drops in crime during his time in office, and credited improved community relations - but acknowledged that with 248 homicides and more than 1,000 shootings in 2014, there was still work to be done.

"Safe is a relative term," Nutter said.

Nearly 3,000 people were killed on 9/11, Nutter said, and the federal government created the Department of Homeland Security because Americans wanted to feel safe.

Every year, 10,000 to 14,000 people are killed nationwide as the result of violence, he continued. Nevertheless, "we have not had a comparable national response to the issue of violence in the United States of America," Nutter concluded.

Tuesday's conversations touched on a variety of issues, from school policing to implicit biases to diversifying police forces.

Panelist Jennifer Eberhardt, a Stanford University psychology professor, praised the increasing use of body cameras at departments around the country - whose footage can be used as evidence in investigations of use-of-force incidents.

Several called before the task force highlighted the importance of training in helping officers recognize and fight against biases.

Richard Beary, the president of the International Association of Chiefs of Police, praised a particular program in Florida - and then told panelists that the state allocates just $67 per officer per year for such training. "What kind of training can you do for $67 per employee?" he asked.

Responding to a question from panelist Brittany Packnett, the director of Teach for America in St. Louis, about whether police bear greater responsibility in bridging the gap with community members, Fraternal Order of Police president Chuck Canterbury said officers "shouldn't be held to any kind of a higher standard."

"But we should take the lead," he said.

A rise in assault and ambush attacks on police have forced officers to become very wary, Canterbury said, adding that the assassination of two New York police officers last month has made officers more distrustful.

Packnett, who lives near Ferguson and has participated in protests since Brown's killing, said she was struck by "heartfelt" testimony from community members.

"Today's another step - Day 158," she said, referring to the time passed since Brown's death. "It's another reminder that the work is necessary."