The conference was scheduled hours before city officials return to court this afternoon to argue over whether the city can independently pass legislation to limit gun sales here.

The mayor has already signed legislation backed by City Council. The National Rifle Association and other groups, including gun dealers, have filed a civil lawsuit to block the laws.

With Police Commissioner Charles H. Ramsey at his side along with gun expert Joseph Vince and city solicitor Shelley R. Smith, Nutter said there are three simple points behind the legislation he signed.

First, the legislation will not impact lawful purchases. Second, federal authorities recommend such legislation as a way to curb gun violence. Third, the gun dealers trying to stop the legislation are ones that engage in multiple sales to a single purchaser - and those guns often end up at crime scenes, Nutter said.

"These gun traffickers are not going to stop us from keeping the citizens of Philadelphia safe," Nutter said.

Ramsey noted that while homicides are down 24 percent this year, 80 percent of the murders are committed with guns. Additionally, he said, nearly 2,000 guns have been confiscated so far this year in the city.

"We've got to do something," Ramsey said. "And these laws go a long way for putting in place reasonable steps to protect the citizens of Philadelphia."

The mayor acknowledged that the city is fighting the NRA, a strong lobbying group that has successfully stopped legislation at the state and federal levels.

Nutter said he can't understand why the NRA would not support legislation that would stop criminals from obtaining weapons, why multiple purchases - sometimes numerous guns bought within five days - are needed or why the sale of assault rifles should be legal.

Enforcing the pending legislation, however, appears to be an uphill fight for the mayor.

A Philadelphia judge appears poised to grant the NRA's request to block enforcement; the fight likely will continue to the Pennsylvania Supreme Court.

Previous rulings by the high court established that the state regulates firearms, not the city.

Nutter, however, said that does not deter him and said the city's expert, Vince, formerly of the federal Bureau of Alcohol, Tobacco and Firearms, will be in court this afternoon to testify that those gun shops trying to ban the legislation are responsible for large amounts of multiple sales and guns found at crime scenes.

"We are talking about illegal guns in the hands of criminals," Nutter said.