IN THE THREE DAYS since a Virginia Tech student gunned down 32 people in the deadliest shooting rampage in modern U.S. history, gun-rights activists have been saying the disaster could have been averted if students had been armed to stop their murderous stalker.

But Philadelphia police say three recent incidents instead prove why the proliferation of guns represent more problems than protection in a city plagued by more than 2,000 shootings last year.

* Police believe the same armed mugger is responsible for three shootings in the Northeast in the past three weeks that have hospitalized three people, including a 12-year-old girl. In all three cases, the robber began blasting his gun when his victims resisted, said Capt. John McGinnis of Northeast Detectives.

The first incident occurred at 7 p.m. March 30, when the mugger approached a man on Valley Street near Harrison in East Frankford, said Lt. Mark Burgmann of Northeast Detectives. The victim pulled his own gun and the men got into a shootout. A 12-year-old girl playing nearby caught some stray bullets in the chest and arm; she is recovering, Burgmann said.

The second incident occurred on April 6 at 3:30 p.m., when the mugger accosted a 19-year-old man on Griscom Street near Adams Avenue in Frankford, Burgmann said. That victim suffered four gunshot wounds to his chest and arm, he added.

About 10 hours later, the robber struck again on Dyre Street near Duffield in East Frankford, shooting another 19-year-old man in the chest and back, Burgmann said.

In all three cases, the victims' description of their assailant matched and the bullets were the same caliber, Burgmann said.

Police have a person of interest they are seeking for questioning, McGinnis said. So that robbery victims can avoid injury, he urged them to comply with muggers' demands and to "be a good witness" by reporting details of their crime to police promptly.

* A 14-year-old girl and 17-year-old boy were charged with gun offenses Tuesday, after they were found with a loaded .45-caliber pistol just before dismissal outside Abraham Lincoln High School in Mayfair. A tipster had alerted police that "trouble" was expected between feuding teens, some of whom were believed to be Lincoln students, McGinnis said. The girl had been holding the weapon for her boyfriend, he added. A school district spokeswoman couldn't be reached for comment.

* A judge this week acquitted a Northeast Philadelphia man who pointed a gun at a coach during his son's peewee football game in Burholme Park last October.

While the defense successfully argued Tuesday that Wayne Derkotch, 41, pulled his pistol in self-defense after coach Jermaine Wilson repeatedly punched him, police complained that prosecution witnesses who told them that Derkotch instigated the incident failed to show up in court, ensuring an acquittal. The Oct. 22 altercation erupted after spectators complained that Wilson wasn't allowing the team's benchwarmers to play during a "B game" intended to give the less-talented 5- and 6-year-old footballers time on the field.

Attorney Brian E. Quinn said his client's decision to brandish his legally permitted .357 Magnum revolver halted a dangerously escalating incident.

"What would have happened to Mister Derkotch if he didn't have a gun on him? [Wilson] could have killed him," Quinn said, noting that Derkotch lost a tooth in the fracas and suffered a blow that swelled his eye shut.

Prosecutor Randy Hsia argued that Derkotch's response was too severe for what amounted to a fistfight.

"I don't think that the force used against the defendant rose to the level of [Derkotch's] using a gun in response."

McGinnis agreed, saying: "The Constitution gives you the right to bear arms, and I very much believe in the Constitution. I carry a gun if I'm going into a very, very bad neighborhood. But why would you take a gun to your kid's peewee football game? Bad things occur with guns." *