Civil rights advocates criticized plans by the Los Angeles Police Department to map the city's Muslim communities, calling it racial profiling.

The LAPD's counterterrorism bureau plans to identify Muslim enclaves in order to determine which might be likely to become isolated and susceptible to "violent, ideologically based extremism," said Deputy Chief Michael P. Downing on Thursday.

"We want to know where the Pakistanis, Iranians and Chechens are so we can reach out to those communities," said Downing, who heads the counterterrorism bureau.

Downing said the plan is still in its early stages, but the LAPD wants to work with a Muslim partner and intends to have the data assembled by the University of Southern California's Center for Risk and Economic Analysis.

Downing testified about the plan before a U.S. Senate committee on Oct. 30.

In his testimony, Downing said his bureau wanted to "take a deeper look at the history, demographics, language, culture, ethnic breakdown, socioeconomic status and social interactions" of the city's Muslim communities.

There are an estimated 500,000 Muslims in Los Angeles, Orange and Riverside counties.

On Thursday, several Muslim groups and the American Civil Liberties Union of Southern California sent Downing a letter expressing "grave concerns" about the program.

"Singling out individuals for investigation, surveillance, and data-gathering based on their religion constitutes religious profiling that is just as unlawful, ill-advised and deeply offensive as racial profiling," said the letter.

It was signed by representatives of the ACLU of Southern California; Muslim Advocates, a national association of Muslim lawyers; the Islamic Shura Council of Southern California and the Council on American-Islamic Relations.

The plan "basically turns the LAPD officers into religious political analysts, while their role is to fight crime and enforce the laws," said Hussam Ayloush, head of the Los Angeles chapter of the Council on American-Islamic Relations, who signed the letter.

However, another group, the Muslim Public Affairs Council, is considering working with the LAPD on the project.

"We will work with the LAPD and give them input, while at the same time making sure that people's civil liberties are protected," said Salam al-Marayati, the council's executive director.