With a store that sells everything from Pedro Infante CDs to comforters and phone cards, Don Pedro's is a kind of thoroughfare in Fells Point, and Rivera knows the mood of the neighborhood well.

"For my friends, for my customers, for my employees, any time they come in contact with the police, it's an invitation to be asked for paperwork, to get caught."

Rivera settled in Fells Point 12 years ago because she felt Baltimore was an immigrant-friendly city. Back then, a handful of Hispanic businesses dotted a neighborhood that today teems with restaurants, music stores and bars. The city's Hispanic population, nearly 26,000, has more than doubled over the past decade, and much of that growth has taken place west of Patterson Park.

Advocates for immigrants say the city's efforts to connect with that growing population have been effective.

"We've actually made some progress, and that's part of why the implementation of this program has such a damaging effect," said Elizabeth Alex, a lead organizer for Casa de Maryland, which opposes Secure Communities. "We don't go want to go backward."

Even though it is not their program, city leaders are now scrambling to explain it to residents. Police Commissioner Frederick H. Bealefeld III, who declined to be interviewed for this article, plans to talk with immigrant leaders this week. The mayor's Hispanic liaison started making calls into the community immediately after the city was notified that Secure Communities would be activated.

"It had been our hope that ICE would do a lot of community outreach around this, explaining how it works," said Sheryl Goldstein, director of the mayor's office on criminal justice. "Their failure to do that in our community has left people very confused."

Goldstein stressed that the city's police officers are not surrogate immigration agents.

"If you're a victim of a crime or you report a crime, you're not going to be fingerprinted," she said. "We want [victims] to come forward, and we want to assure them the best that we can that this program is not going impact them."

The program has received criticism in other cities, too. In a statement last year, the Major Cities Chiefs Police Association, which counts Baltimore as a member, said the program "undermines the trust and cooperation with immigrant communities."

ICE spokeswoman Nicole A. Navas said the program is consistent with the Obama administration's broader goal of prioritizing the deportation of serious criminals. Ninety-four percent of people removed from the country under Secure Communities, she said in a statement, are "convicted criminals, recent illegal border entrants and those who game the immigration system."

Nationally, the program has identified about 780,000 illegal immigrants since 2008, according to ICE data. Of that number, 162,940 have been deported. The largest share of those deportations, about 30 percent, were convicted of a crime punishable by less than one year in jail. A further 27 percent were convicted of aggravated or multiple felonies.

Supporters of the program focus on the second number, while opponents tend to highlight the less serious offenses.

"Instead of targeting the worst of the worst, it is a wide-sweeping dragnet that is catching people who have not committed [major] crimes but low-level offenses," said Laura Vazquez, an analyst at the National Council of La Raza.

For some proponents of the program, the distinction is largely irrelevant. Ira Mehlman, a spokesman for the Federation for American Immigration Reform, said the U.S. government should remove all illegal immigrants. Otherwise, he said, the administration sends a message that undocumented immigrants can stay in the country as long as they do not commit a serious crime.

"The idea that people who are violating the law should have complete peace of mind is illogical," he said. "If you're violating the law, if you're in the country illegally, then you probably should be a little nervous."

In Maryland, 670 people have been deported under the program, which was previously in place for every jurisdiction in the state except Baltimore City and Montgomery County. Thirty percent of those deported from the state were immigrants who had been removed from the country at least once before.

Even as the Obama administration expands Secure Communities — officials hope to have the entire nation covered next year — it is also pursuing a policy that would give immigration prosecutors wider discretion to drop cases when defendants have no prior criminal record and are closely tied to their communities. Baltimore was selected last year as one of two pilot cities to test that policy.

Advocates hope Ayala is a good candidate to have his case suspended. He traveled back and forth to El Salvador for 15 years on tourist visas and said he decided to stay here after his most recent visa expired because his life was threatened back home. He said he has applied for asylum and that the request is pending.

Ayala attends church, holds a steady job and, when home, is surrounded by a coterie of grandchildren. He said that he rarely drives but had to the day he was pulled over because the school his grandchildren attend had an early dismissal. No one else in the family was available to pick them up.