State troopers joined Philadelphia police on street patrols last night in an effort to combat the gun violence that left four bystanders wounded this week and keeps pushing up the city's homicide count.

The initiative began at 6, only hours after Police Commissioner Sylvester M. Johnson announced Operation Trigger Lock, which will target hoodlums carrying weapons in high-crime neighborhoods.

The number of troopers involved in the operation was not disclosed, nor were the specific areas where they would be deployed. The troopers will ride with city Highway Patrol officers in marked state police cars.

The police union president, Bob Eddis, said the move reflected "incompetence in management" and called for Johnson to step down or be replaced.

"Bringing in outside help is a slap in the face to our officers," Eddis said. "The commissioner should be deploying his personnel differently."

Johnson, who had resisted calling in the state police or National Guard to back up city police, said yesterday that the initiative had been in the works for several months.

"We need them, we appreciate them, we're glad to have them," Johnson said of the troopers.

Jack Lewis, the state police spokesman, said Gov. Rendell initially proposed that the state police look at ways to help Philadelphia, and that the program came together this week with funding from the Pennsylvania Commission on Crime and Delinquency.

Johnson, standing with his own commanders and officials from the state police and governor's office, said the program did not signal a state police takeover or a crime emergency in the city.

"They didn't say, 'We want to come in there and start patrolling your streets,' " Johnson said. "What they basically said is, 'We want to come in there and work with you, let's work as partners.' "

Philadelphia joins 17 other municipalities in Pennsylvania, including Chester and Allentown, in using state troopers to beef up their forces in fighting street crime. New Jersey state police have been patrolling in Camden since 2002.

The move, besides putting more police on the street, comes without the financial cost the city would encounter by hiring officers or paying overtime.

Lewis said other areas covered by the state police force, which has more than 4,500 troopers, will not be affected by the local operation.

The troopers who patrol the city will do so in addition to their regular duties at Troop K on Belmont Avenue and will be paid overtime, he said.

Michael Kane, executive director of the Pennsylvania Commission on Crime and Delinquency, said Philadelphia received about $4 million of a $10 million statewide program to hire police officers. The program had $257,000 remaining and the commission decided to earmark that money for this effort.

He said he did not immediately know how much police presence the grant would buy.

Republican mayoral candidate Al Taubenberger welcomed the program.

"It gets additional police in areas that need it," he said. "But additional police is one - and only one - component of stopping gun violence."

Democrat Michael Nutter's mayoral campaign said the candidate, who has been endorsed by Eddis' Fraternal Order of Police lodge, wanted to learn more about the operation before commenting.

The news caught some in Harrisburg by surprise, including Rep. Ronald Marsico (R., Dauphin), the ranking Republican on the House Judiciary Committee.

Hearing of the plan from a reporter, he called it misguided, especially since the Rendell administration has proposed to close or reduce service at several barracks across the state.

"First off, Philadelphia already has the largest police force in the state, even larger than the state police," Marsico said. "It's clear that the governor wants the state police to do more with less, except when it comes to his hometown.

"He has proven to me . . . that he is only concerned about one region of the state."

The city is on pace to surpass last year's total of 406 homicides, although shootings overall were down 9.5 percent as of Aug. 20.

Lawrence Sherman, director of the Jerry Lee Center for Criminology at the University of Pennsylvania, said putting more police in high-gun crime areas can only help.

He said that even though the operation may not seize large numbers of guns, the added police presence is a deterrent.

"Anything that persuades people to leave their guns at home and not have them out out on the street would reduce gun violence," he said. "We're at a point now of trial and error."

Bruce A. Edwards, president of the state troopers union, said residents should not expect a major drop in violent crime citywide.

"It's not anything different than what we do in other cities," he said, "but due to the city's size, with one of the largest police forces in the nation, a small force of troopers helping out isn't going to have the impact that it does in a borough or a small city that only has 150 officers."

"It's not like we are coming in there in force," Edwards said.