Philadelphia's agreement to share arrest data with federal immigration enforcement agents will be extended for one year, with a critical change: Names of victims and witnesses will no longer be available, Mayor Nutter announced Friday.

The adjustment - worked out by Police Commissioner Charles H. Ramsey, Municipal Court President Judge Marsha Neifeld, and District Attorney Seth Williams, and accepted by U.S. Immigration and Customs Enforcement (ICE) - addresses concerns by pro-immigrant groups that information in preliminary arrest reports could expose victims and witnesses to deportation proceedings, the mayor said.

Many immigrants, both legal and illegal, are reluctant to cooperate with police for fear of deportation, advocates say.

The new arrangement allows ICE agents to scrutinize computer arrest records for defendant information. Data fields pertaining to victims and witnesses, however, will be shielded.

The two-year-old agreement under which ICE had access to the city's Preliminary Arraignment Reporting System was set to expire Aug. 31.

"I said on July 1 that we want to have an agreement with ICE, but that we needed to fix and refine the PARS system," Nutter said. "My concerns have been addressed."

The Philadelphia director of ICE assured Nutter that federal agents had never used PARS to target victims and witnesses who were in the United States illegally, he said.

Still, Nutter said, the new arrangement gives him more confidence. Quoting an old saying, Nutter said: "Trust everybody, but still cut the cards."

Nutter urged broad cooperation with police: "Victims should come forward. Witnesses should speak out. No action with regards to their [immigration] status will be taken."

And he used the announcement to address the national debate about immigration, and the estimated 11 million immigrants living illegally in the United States.

"We need to put in place a system which is fair to those from other countries who follow the rules and wait in line for the opportunity to come to America," he said. "But we cannot and must not ignore the plight of the millions of individuals whose status here is undocumented.

"Yes, we need enhanced border control. Yes, we need to focus our efforts on those who pose a threat to our country. But let's not fall into the trap set by the tea party and others who would tell you that every single undocumented individual is a drug smuggler, a terrorist, or a threat to the American way of life. That is simply not true."

When told of the mayor's remarks, Don Adams, president of the Independence Hall Tea Party Political Action Committee, said: "All anyone is asking is for the laws of the land to be respected. Mayor Nutter is off base. He obviously wants to taint the tea party movement."

Some immigrant advocates viewed the PARS changes as generally positive. Others had persistent concerns.

"It is a good step. But it is disappointing on several points," said Zac Steele, community organizer for Juntos, a South Philadelphia advocacy group for Latinos. Steele's group had pushed for the city to terminate the agreement.

"People who are arrested for crimes should stand trial in criminal court for what they did," Steele said. "But I just saw a case Monday of a guy who was still in a holding cell in the local police district" when ICE picked him up.

"I'm glad the city took some step," Steele said. "But I think it falls short of something that will develop true, lasting, deep trust" with immigrant communities.

Williams, a member of the steering committee that crafted the city's new policy, said he joined in the unanimous decision to extend the agreement because "it would be irresponsible" not to.

"The offenders at issue in this discussion are not admirable people just trying to make a better life for their families," said Williams. "They are criminals who most frequently victimize those in the very community in which they live."

Mark Medvesky, a spokesman for ICE in Philadelphia, said the new agreement extends the agency's "excellent" relationship with the city.

"Access to PARS helps ICE enhance public safety," he said, "and assists us in targeting . . . the most egregious offenders."