CHICAGO — Mayor Rahm Emanuel’s first reading material each morning, at 5:30, is not a budget update, a legislative proposal or a packet of headlines. It is an e-mail from the Chicago Police Department listing the crimes that were committed during the night that just ended. By 7 a.m., he is calling Garry F. McCarthy, the police superintendent. That is unlikely to be their final conversation of the day, or even of the morning.


Mr. Emanuel listed safer streets among his top three priorities when he became mayor a year ago, but Chicago, the nation’s third-largest city, is now testing that promise. Homicides are up by 38 percent from a year ago, and shootings have increased as well, even as killings have held steady or dropped in New York, Los Angeles and some other cities. As of June 17, 240 people had been killed here this year, mostly in shootings, 66 more deaths than occurred in the same period in 2011.


“That’s somebody’s husband, somebody’s son, and they’re dying right on our block,” said Maya Hodari, who lives on a South Side street where two shootings have already taken place this year, one of them fatal and another as a toddler looked on. “It hurts.”


The violence has left its largest scars in some of Chicago’s most impoverished, struggling neighborhoods on the South and West Sides, places with views of the city’s gleaming downtown skyline that feel worlds apart. Wealthier, whiter parts of the city have not been entirely immune — shootings were reported in the last few days along the city’s Magnificent Mile shopping district and near the Lincoln Park Zoo — but a majority of the killings have been tied to Chicago’s increasingly complicated gang warfare, police statistics suggest, and to the gritty neighborhoods where gangs have long thrived.


There is no evidence of a broader crime wave; in fact, measures of crime apart from homicides, including rapes, robberies, burglaries and auto thefts, have actually improved by about 10 percent since a year ago.


“We’ve got a gang issue, specific to parts of the city, and we have a responsibility to bring a quality of life to those residents, and we are going to do it,” Mayor Emanuel, visibly vexed, said in an interview on Friday.


“My bigger issue is not only the homicides and shootings,” he added. “It’s what it does to all the legitimate citizens in that community and the kids.”


Gangs in this city have changed over the decades, splintering from a small set of well-established bands into hundreds of tinier groups with alliances so disparate and shifting that even a former Gangster Disciple member from the West Side, who refused to be named but revealed bullet scars during an interview as proof of his rougher days, said he could not begin to keep them all straight. In just the last two years, the police say, 500 monitored gang factions have fractured into more than 600, many of them with stunningly ready access to guns.


In one neighborhood last week, plainclothes officers searched parking lots and old addresses for 30 suspects as part of Superintendent McCarthy’s larger race to dismantle drug and gang operations. At one point, they said, they found themselves staring at a gun aimed at them by a man who was not even on the list of suspects they were searching for. Moments later, the gun lay shining on the ground, an officer’s shot left a bullet hole in a nearby car, and the man, 21, was added to the list of those arrested in the sweep — all before 11 a.m.


As in most of the nation’s big cities, killings have dropped precipitously in Chicago since the 1990s, as the police tried new approaches and crack cocaine faded. In the early 1990s, more than 900 people were killed annually here, a number that has long since shrunk and hovered around the 400s.


Homicides are down so far this year in New York and in Los Angeles, a fact that Mayor Michael R. Bloomberg’s administration in New York has pointed to in defense of that city’s controversial stop-and-frisk program. But Chicago is not alone among major cities dealing with more killings. In Philadelphia, for instance, 173 homicides were reported as of June 20, compared with 143 in the same period last year.