Gov. Ed Rendell yesterday signed a measure designed to better protect law enforcement officers from people who commit crimes with guns.

House Bill 1845 mandates a minimum jail sentence of 20 years for anyone who shoots -- or shoots at -- a police officer. It also will impose longer prison terms for other gun-related offenses.

The governor, former mayor of Philadelphia, signed the bill at Fraternal Order of Police Lodge No. 5 in the city. Philadelphia has been the scene of several fatal shootings of police officers.

"We are still shocked and still outraged by the senseless killing of Sgt. Patrick McDonald last month,'' Mr. Rendell said. "And we still have not forgotten the brutal shooting deaths of Sgt. Stephen Liczbinski, Officer Chuck Cassidy and Officer Gary Skerski, as well as the death of Officer Isabel Nazario.''

He said that from 2002 to 2007, assaults with firearms on law enforcement officers in Pennsylvania increased by 82 percent.

The new law also increases the statute of limitations, from two years to five years, for prosecuting "straw purchases" linked to gun-related crimes. Criminals often use friends without criminal records to buy guns for them, since they can't buy weapons on their own.