CHICAGO, SEPT. 10 -- Police recorded 75 shooting incidents, resulting in 13 deaths, in a rampage of violence here last weekend marked by gang warfare and drive-by shootings.

The weekend's violence -- the worst of the summer -- brought the number of homicides for the year here to almost 100 more than during the same period last year.

Gad Bensinger, chairman of the Criminal Justice Department at Loyola University, blamed the outbreak on drugs, accessibility of weapons and gang-related violence. Chicago police agreed and also cited a hot, humid weekend that capped several days of sticky weather.

"It has rained so many weekends this summer and, with this being the first nice weekend, the gangs seemed to be out in full force," said Sgt. Robert Trusz of a police violent crimes unit.

Bensinger said increased violence here is characteristic of a national wave of homicides, adding: "It's amazing that people always meet violence and criminal justice with surprise. You don't have to be an expert to understand what's going on."

The rampage came as the city awaited the scheduled execution at 12:01 a.m. Wednesday of Charles Walker, convicted of the 1983 murder of a couple in Mascoutah, Ill., during a $40 robbery. Walker, 50, would be the first person executed in Illinois since 1962. Although various groups have tried to appeal the sentence on Walker's behalf, he has asked repeatedly that the execution not be delayed. Today, Gov. James R. Thompson (R) refused to commute the sentence.

"This {execution} is definitely a big event and is being discussed as such, but it will not, as some people think, reduce the rate of violence in the city," Bensinger said.

During the hours between 9 p.m. last Friday and 3 p.m. Sunday, police reported several drive-by shootings around the city, most of them directed at young people. A boy, 15, died after being shot from a passing car Sunday as he stood with friends on a South Side street corner at 3:15 a.m. At about the same time, a boy, 16, sitting on a car hood, was shot to death, and two of his companions were wounded in a drive-by. An 18-year-old man was killed Saturday in a South Side drive-by shooting.

Four people were shot and wounded Saturday when a gunman fired into a crowd of people leaving a South Side dance hall, and no suspects have been found, police said.

Many of the shootings followed arguments, and police said only three arrests had been made.

A police officer from suburban Park Ridge remained in critical condition today from a gunshot wound in the head. Edward Gallagher, 32, was shot on the West Side while off duty Saturday after he and his cousin argued with several occupants of a car. Police said that the shooting appeared to be gang-related and that the suspects were being sought.

John Fildes, 36, an attending surgeon at the Cook County Trauma Center, said the weekend was the worst in the memories of staff members, with 32 admissions on Saturday. A normal number of admissions for a Saturday is 16 to 20, he said.

"The nurses and the physicians ran hard for a good 24 hours straight," Fildes said. "The operating rooms were full, the blood bank was strained and all of our capabilities were strained to saturation. Even the administrators had trouble finding free beds."

Fildes said the trauma center was especially stressed because of the recent closings of two of the city's three other trauma centers.

Jeanette Calloway of the Chicago Crime Commission, a nonprofit organization that assists law enforcement members and crime victims, said: "There is really nothing you can do to prevent random shootings that happen like this, except to try to figure out a way to get the people off the streets that have nothing to do but shoot other people. When it's this big, it's beyond simple prevention."