Average citizens who quietly band together and adopt radical ways pose a mounting threat to U.S. security that could exceed that of established terrorist groups like Al Qaeda , a new police analysis has concluded.

The New York Police Department report released Wednesday describes a process in which young men — often legal immigrants from the Middle East who are frustrated with their lives in their adopted country — adopt a philosophy that puts them on a path to violence.

The report was intended to explain how people become radicalized rather than to lay out specific strategies for thwarting terror plots. It calls for more intelligence gathering, and argues that local law enforcement agencies are in the best position to monitor potential terrorists.

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"Hopefully, the better we're informed about this process, the more likely we'll be to detect and disrupt it," Police Commissioner Raymond Kelly said during a briefing with private security executives at police headquarters.

The findings drew swift criticism from an Arab anti-discrimination group, which accused the NYPD of stereotyping and of contradicting recent federal warnings that the chief terror threat lies abroad.

"It plays right into the extremists' plans because it's going to end up angering the community," said Kareem Shora, legal adviser for the American-Arab Anti-Discrimination Committee.

In a statement, Department of Homeland Security spokesman Russ Knocke said federal authorities "appreciate efforts to better understand the phenomenon of radicalization."

"We are fortunate that radicalization seems to have less appeal in the U.S. than in other parts of the world," he said, "but we do not believe that America is immune to homegrown terrorism."

The FBI declined comment.

The study is based on an analysis of a series of domestic plots thwarted since the Sept. 11 terrorist attacks, including those in Lackawanna, New York; Portland, Oregon; and Virginia. It was prepared by senior analysts with the NYPD Intelligence Division who traveled to Hamburg, Madrid and other spots around the world to confer with authorities about similar cases.

The report found homegrown terrorists often were indoctrinated in local "radicalization incubators" that are "rife with extremist rhetoric."

Instead of mosques, those places were more likely to be "cafes, cab driver hangouts, flop houses, prisons, student associations, non-governmental organizations, hookah bars, butcher shops and bookstores," the report says.

The Internet also provides "the wandering mind of the conflicted young Muslim or potential convert with direct access to unfiltered radical and extremist ideology."

The threat posed by homegrown extremists — from "eco-terrorist" groups to neo-Nazis — has long been a top concern for federal counterterror officials.

Recently, authorities have taken a closer look at radicalization happening in U.S. prisons, where a study last year by George Washington University and the University of Virginia found that Islamic extremists were turning jail cells into terrorist breeding grounds by preaching violent interpretations of the Quran to their fellow inmates.

The NYPD report warns that more intelligence gathering is needed since most potential homegrown terrorists "have never been arrested or involved in any kind of legal trouble," the study says.

They "look, act, talk and walk like everyone around them," the study adds. "In the early stages of their radicalization, these individuals rarely travel, are not participating in any kind of militant activity, yet they are slowly building the mind-set, intention and commitment to conduct jihad."

The Council on American-Islamic Relations accused the NYPD analysts of distorting the innocent behavior of observant Muslims.

"Is Islamic attire or giving up bad habits ... now to be regarded as suspicious behavior?" asked the group's chairman, Parvez Ahmed.

A recent report by the U.S. government — the National Intelligence Estimate — concluded that Osama bin Laden's network had regrouped and remains the most serious threat to the United States.

Kelly insisted the NYPD report made no effort to provide a "cookie-cutter" profile for terrorists. He also argued that the NYPD report "doesn't contradict the National Intelligence Estimate — it augments it."

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