MAYOR NUTTER delivered harsh words yesterday as he offered a $20,000 reward for information leading to the arrest and conviction of "the coward" who fired a semiautomatic weapon at a crowd watching an outdoor basketball game Monday night at Kingsessing Recreation Center, wounding six people.

"We will not tolerate this kind of insane, asinine, idiotic behavior at any of our facilities . . . definitely not at a recreation center," the mayor said.

These "safe havens" are "off limits, off limits to this kind of egregious, heinous behavior," Nutter said, his voice rising.

To the gunman, the mayor said at a news conference at the rec center with Police Commissioner Charles Ramsey and other officials: "We'll find your little butt and lock you up."

A couple of weeks ago, Nutter designated the Kingsessing center as one of 20 recreation facilities that would stay open later hours, until 10 p.m., on Fridays and Saturdays, to give young people a safe place to hang out.

Monday's shooting happened about 8:50 p.m. during halftime at an adult-league basketball game.

"It doesn't matter," Nutter said. "Ten years old, 50 years old, you should be able to be at a rec center in the city of Philadelphia and not have to worry about anything happening to you."

Police Inspector Dennis Wilson, of the Southwest Division, told reporters that the gunman descended the stairs between the rec center and the basketball court with an "outstretched arm," pointing a gun, believed to have been a .40-caliber semiautomatic, and shot at least nine times toward the bleacher area.

One man, who was shot in the stomach and remained in critical condition at the Hospital of the University of Pennsylvania, may have been the intended target, Wilson said. Police have not yet been able to speak to that man.

The other victims, four men and a woman, all shot in their legs, also were still in the hospital. All the victims were between 18 and 23 years old, Wilson said.

An estimated 500 people were at the game, but police were still seeking someone who could identify the shooter.

Two police officers from the 12th District, which covers Kingsessing and Southwest Philly, were working Monday night and watching over the game for any disturbances. They chased the gunman after he ran and slipped through a hole in a rec-center fence onto Chester Avenue, near 51st Street, but then lost him.

Nutter said that the $20,000 reward would come from a new $500,000 reward fund that he created, which is in the city's budget "for instances like this." He urged people to call police at 215-686-3183, or to go to www.phillypolice.com and click on the "Submit a Tip" link.

Wilson said that the gunman was black, in his mid-20s, about 5 feet 8, and was wearing a white T-shirt and black jeans.

On Aug. 8, Nutter announced an earlier summer curfew of 9 p.m. on Fridays and Saturdays for minors under 18 in Center City and University City in response to attacks by violent youth mobs on random victims.

Everett Gillison, deputy mayor for public safety, said yesterday that Nutter had asked him to recommend options regarding the earlier curfew, including whether to extend it past the summer, broaden it citywide or make it even earlier.