WASHINGTON — In a single week last April, 3 people were killed with guns in Philadelphia, 14 more were shot and wounded, 68 robberies were carried out at gunpoint and a total of 144 crimes involving firearms were reported.


During that same week in San Diego, a city of roughly the same size with far fewer police officers, there were no gun-related homicides, 2 people wounded by gunshots, 4 robberies committed at gunpoint and a total of only 20 gun-related crimes.


What made the difference? About 250 police chiefs from around the country debated this question and gun violence more generally at a meeting here this week, taking as their focus a survey of crimes occurring in six cities — Philadelphia, San Diego, Milwaukee, Minneapolis, Austin, Tex., and Toronto — over a seven-day period in April 2011. The survey was carried out by the Police Executive Research Forum, a nonprofit police research group that sponsored the session as part of its two-day annual meeting.


Coming two months after the shooting death of Trayvon Martin in Florida, the wide-ranging discussion encompassed the proliferation of laws that make it easier to own, carry and use a gun; the role of gangs and narcotics; the characteristics of perpetrators and victims; and the need for more aggressive prosecution and greater investment in technology to trace and identify firearms.


If there was a central message to be drawn from the survey, it was that gun violence is tightly concentrated in the poorest urban neighborhoods, its victims mostly minorities, who receive little attention from politicians and the news media.


“Nobody in this room, unless you’re from Sanford, Fla., would even know the name of Trayvon Martin if it was a black kid that had shot Trayvon Martin,” said Police Commissioner Charles H. Ramsey of Philadelphia, who is African-American.


“It happens every single day in Philadelphia. It happens every single day in cities across the country, but if it’s a black killing a black,” no one cares, Commissioner Ramsey continued, noting that the week studied by the forum was less violent than many other weeks in Philadelphia. “Our streets are bleeding, and they’re bleeding profusely.”


The survey found that, using conservative estimates, the cost to taxpayers of the crimes committed with firearms during the week of April 4 to April 10 was more than $38 million in medical care, social services, criminal justice costs and other expenses.


In many cases, the victims of the crimes resembled the perpetrators. During the week in Philadelphia, for example, a 20-year-old woman known as Peanut who had five prior criminal convictions and arrests stretching back to the age of 13, was responsible for two shootings on two different days. Her second victim, shot 16 times, was a drug dealer who is now in a wheelchair but refused to cooperate with the police.


In Milwaukee, which had 2 homicides, 40 robberies with firearms and 12 people shot and wounded, 40 percent of the victims that week had criminal records, said Police Chief Edward A. Flynn of Milwaukee.


Police Superintendent Garry F. McCarthy of Chicago, where homicides rose sharply in the first three months of this year, said the fact that in Illinois, as in some other states, people are not required to report the transfer, loss or theft of a gun adds to the problem. A revolver recovered in the recent shooting of a police officer, he said, was bought in 1972 by a 52-year-old woman, but what happened after that is unrecorded.


“The question is, where has that gun been all this time?” he asked.


Several police chiefs complained that even when suspects are convicted in gun crimes, they sometimes do not go to prison. One reason for the reduced number of crimes in San Diego, some participants suggested, might be California’s tougher laws, which mandate 10 years in prison for a crime involving a gun, 20 years if the gun is fired, and 25 years to life for killing or seriously injuring someone with a gun. The spread of concealed carry laws and statutes like Florida’s that expand the legal use of deadly force in self-defense also came in for criticism.


Chief Flynn recounted pleading with a state senator to include a provision in Wisconsin’s concealed weapons law that would ban habitual criminal offenders from obtaining permits. The senator, he said, told him, “Here’s the phone number of the National Rifle Association lobbyist in Washington, D.C. If it’s O.K. with him, it will be O.K. with us.” The provision was not included, Chief Flynn said.


Straw purchasing, in which a proxy buys guns for convicted felons, is another problem, participants said. Chief Art Acevedo of Austin said his officers regularly observed women buying as many as 30 guns, including semiautomatic weapons, at gun shows and then passing them on to men. Austin had 39 gun crimes during the survey week, including 20 robberies at gunpoint and 11 aggravated assaults.


Identifying the causes of gun violence, however, is easier than finding solutions, the police chiefs present conceded, and better policing will not be enough to solve it.


“This is a crisis, it’s a terrible problem,” Commissioner Ramsey of Philadelphia said. “We do own a good part of it, but others have to step up to the plate.”