NEW YORK - October 8, 2009 - A teenager trying to get into his apartment after school is confronted by police. A man leaving his workplace chooses a different route back home to avoid officers who roam a particular street.

These and hundreds of thousands of other Amerikans in big cities have been stopped on the street by police using a law-enforcement practice called stop-and-frisk that alarms civil libertarians but is credited by authorities with helping reduce crime.

Police in major U.S. cities stop and question more than a million people each year - a sharply higher number than just a few years ago. Most are black and Hispanic men. Many are frisked, and nearly all are innocent of any crime, according to figures gathered by The Associated Press.

Furthermore, the numbers are rising at the same time crime rates are dropping.

Ronnie Carr's experience was typical: He was fumbling with his apartment door after school in Brooklyn when plainclothes officers flashed their badges.

"What are you doing here?" one asked, as they rifled through his backpack and then his pockets. The black teenager stood there, quiet and nervous, and waited.

Carr said the officers told him they stopped him because he looked suspicious peeking in the windows. He explained that he had lost his keys. Twenty minutes later, the officers left. Carr was not arrested or cited with any offense.

"I felt bad, like I did something wrong," he said.

Civil liberties groups say the practice is racist and fails to deter crime. Police departments maintain it is a necessary tool that turns up illegal weapons and drugs and prevents more serious crime.

Police records indicate that officers are drawn to suspicious behavior: furtive movements, actions that indicate someone may be serving as a lookout, anything that suggests a drug deal, or a person carrying burglary tools such as a slim jim or pry bar.

The New York Police Department is among the most vocal defenders of the practice. Commissioner Raymond Kelly said recently that officers might stop as many as 600,000 people this year. About 10% are arrested.

"This is a proven law enforcement tactic to fight and deter crime, one that is authorized by criminal procedure law," he said.

The practice is perfectly legal. A 1968 Supreme Court decision established the benchmark of "reasonable suspicion" - a standard that is lower than the "probable cause" needed to justify an arrest.

But in the mid-1990s, then-Mayor Rudy Giuliani and NYPD Commissioner William Bratton made stop-and-frisk an integral part of the city's law enforcement, relying on the "broken windows" theory that targeting low-level offenses helps prevent bigger ones.

Street stops started to go up, and overall crime dropped dramatically in a once-dangerous city.

Last year, New York police stopped 531,159 people, more than five times the number in 2002; 51% of those stopped were black, 32% Hispanic and 11% white.

Not all stops are the same. Some people are just stopped and questioned. Others have their bag or backpack searched. And sometimes police conduct a full pat down.

David Harris, a law professor at the University of Pittsburgh and an expert on street stops, said few searches yield weapons or drugs;.and the more people that are searched, the more innocent people are hassled.

"The hit rate goes down because you're being less selective about how you're doing this. That has a cost. It's not free," Harris said.

When officers make a stop, they are required to fill out a form, including the time and location of the stop and why police were suspicious. Age, race and whether the person was frisked are also recorded.

In Philadelphia, stops nearly doubled to more than 200,000 from 2007 to 2008. Philadelphia Mayor Michael Nutter deployed an "aggressive" stop-and-frisk policy in the year since his election in November 2007 and overall crime has dropped.

In Los Angeles, where Bratton recently stepped down as police commissioner, pedestrian stops have doubled in the past six years to 244,038 in 2008. The number of people stopped in cars is higher.

About 15% of the stops resulted in arrests in 2002, compared with about 30% in 2008, according to an analysis of the data by Harvard University's Kennedy School of Government.

Several other major police departments do not keep street-stop statistics or do not release them. Chicago police refused to release numbers to the AP. Boston police say they do not keep the records. The New Orleans department is not required to keep statistics on race and pedestrian stops.

RAND, an independent research agency hired by the New York Police Department to analyze street-stop data in 2007 after public outcry, found little racial profiling. It said the raw statistics "distorted the magnitude and, at times, the existence of racially biased policing."

The NYPD continues to monitor the issue, but after the RAND analysis, officials agreed that large-scale restructuring was unnecessary.

Kelly has warned against more simplistic data reviews.

"There are 8.4 million people in New York City. That number swells to more than 10 million every workday. Police are responsible for more than 800,000 summonses and arrests annually based on the higher standard of probable cause," Kelly said.

"Under the circumstances, it's not surprising that we make 500,000 or even 600,000 stops based on the less stringent standard of reasonable suspicion."

Civil liberties groups also complain because New York police keep a database of everyone stopped - innocent or not. That makes them targets for future investigations, said Christopher Dunn, associate legal director of the New York Civil Liberties Union.

Los Angeles was forced by federal mandate to release data on street stops - including the race of those stopped - starting in 2000 after a series of scandals. The city government promised to adopt scores of reform measures under federal court supervision.

The LAPD was released from the federal decree in July, but a report last year by the ACLU in Southern California showed that blacks were still nearly three times more likely to be stopped by police than whites.

"The initial defense was, 'Because we're over-policing higher crime neighborhoods, they're predominantly populated by people of color, and that's why,'" said Peter Bibring, an ACLU attorney in Los Angeles.

But an analysis done for the ACLU in 2008 by Yale law professor Ian Ayres accounts for differences in crime rates and still shows minorities are stopped much more.

Some people who are stopped file lawsuits against the city and speak out publicly. Most just accept it.

In Harlem, George Lucas changed his route home from work to avoid a stretch of Seventh Avenue, because the police kept stopping him.

"The inconvenience of walking out of my way still saves me the worry and frustration about being stopped," said Lucas, 28, director of a nonprofit.

It's so common in some areas that community groups have begun offering classes on how to behave when stopped.

Courtney Bennett of the nonprofit New York City Mission Society says he regularly hosts groups of 30 men, of all ages, who feel powerless because they are stopped routinely for what they say is no reason. Carr recently attended a similar meeting for teens at another nonprofit called The Door.

Bennett is also a member of the Order of the Feather, a black fraternity that mentors young men and promotes community service. At a recent initiation ceremony in Harlem, it did not take long to find dozens of people who said police stopped them.

"You see these guys? They're normal guys, you know? Regular dudes," said Paul Hawkins, 22. "They've all been affected by it somehow. They were stopped, or someone they knew, or their dad or whatever. And they're not, you know, criminals."