"There is an intolerably high level of unlawful stops and frisks," it said. "Unless there is a dramatic change in the practices, we will be compelled to seek judicial relief."
The monitoring program was part of the Nutter administration's 2011 settlement to end an ACLU lawsuit that accused the police of using racial profiling to determine whom to stop.
Police Capt. Francis Healy, an attorney with the department, said the problems cited in the report were mainly due to officers improperly explaining the justifications for their stops and searches.
"We're kind of getting beaten up for it because their articulation is not great," said Healy, a special adviser to Commissioner Charles H. Ramsey. "I don't believe the stops are unconstitutional."
Healy said the department was cooperating with the ACLU to make certain that all stops are lawful and properly described. He stressed that police know that "we can't alienate the community we serve."
Nutter made the stop-and-frisk program a key part of his 2007 mayoral campaign, promising that it would bring down crime. Police statistics show the number of gun robberies and assaults with firearms have dropped sharply since Nutter took office in 2008, down 20 percent and 11 percent respectively. Police reported the same number of homicides last year as in 2008, but the murder rate is down so far this year.
The theory behind the stop-and-frisk program, which is practiced in numerous cities, is that intense police pressure on high-crime areas gets guns off the street. Police legally can frisk pedestrians if there is a reasonable suspicion of criminal activity. Experts say training is essential to ensure that officers know when they are allowed to conduct stops and searches.
In 2009, police stopped more than 250,000 people, mainly black and Latino men, according to the original lawsuit. Because Philadelphia's high-crime areas tend to be in minority communities, allegations of racial profiling quickly surfaced.
Among the plaintiffs in the initial lawsuit were numerous Latino and black professional men, including former State Rep. Jewell Williams - now Philadelphia's sheriff - who were stopped under the program.
At the time of the settlement, Nutter said the agreement - requiring the city to provide the ACLU with reports on thousands of stops each year - would help restore the public's trust in the police.
The report said police have been reducing the number of stops, down 15 percent last year. Police are supposed to cut back the frequency of stops when the program has successfully reduced crime.
In addition to ACLU review, department officials in each police division have audited samplings of stops. They have found few incidents in which officers did not have legal justifications for conducting stops.
The report questioned those low numbers.
It said that in the high-crime East Division, the department's audits found that officers had reasonable suspicion to frisk people in every incident that was audited for the first quarter of 2012. In the Northeast Division, where the department audited 393 stops during the second quarter of 2012, not a one was deemed to be improper, it said.
"In our view, the audits conducted by the city for these two quarters are flawed," the report said.
Healy said police inspectors responsible for the audits "are seeing things from the police perspective," just as doctors often can read the writing on seeming indecipherable prescriptions.
"The inspectors may unintentionally be reading between the lines," Healy said. "I think the inspectors are giving the officers credit for what they think the officers are saying."
Attorney Paul Messing, who worked with the ACLU monitoring, said his group found more than twice as many illegal stops as it expected when it filed the original lawsuit against the city. He said the program also produced few firearms seizures, with police finding only one gun for roughly every 1,000 stops.
"This program was implemented in a very unproductive way," he said.
Messing, a lead counsel for the plaintiffs, said the problems would not be solved by just teaching officers to properly complete their paperwork.
"We all need to find a way to prevent thousands of bad stops and frisks," he said. "We hope the city and the police department will take the steps soon, so that court intervention is not necessary."
Contact Mark Fazlollah at 215-854-5831 or firstname.lastname@example.org .