Denney says the program makes Hispanics suspicious of policeand less willing to cooperate to solve crimes.

"There has to be a level of trust that both sides enjoy in order to work together," he says. "There are going to be times when we have to rely on illegal immigrants to conduct an investigation, and they are going to be concerned if the first thing they think is we're going to round them up."

The program has supporters, including Lexington County, S.C., Sheriff James Metts, whose department joined this year.

Metts says his area's agriculture industry has drawn a large influx of Hispanics and that he has seen "several murders, gang activity, drug activity, coming in with the Hispanic population."

His office did not provide statistics but cited cases in which illegal immigrants were suspects in violent crimes and a 2008 study that found 8.5% of the people in his jail were in the country illegally.

"We're not trying to profile any particular area, race or whatever," Metts says. "We're just trying to keep the quality of life in our community."

Critics of the program, including the National Council of La Raza, a Hispanic civil rights organization, say it leads to racial profiling. Supporters, including the Center for Immigration Studies, which advocates tighter immigration controls, say it's a needed tool in the absence of tough federal enforcement.

Using local police to enforce immigration law was at the heart of Arizona's immigration law, which would require the state's 15,000 law enforcement officers to check the immigration status of people stopped for another offense if there was "reasonable suspicion" they were in the country illegally. The core of the law was put on hold by a federal judge; Republican Gov. Jan Brewer is appealing that ruling.

Richard Rocha, a spokesman for Immigration and Customs Enforcement (ICE), says part of the reason for the decline in interest in the program is the economy.

"Law enforcement agencies across the country are faced with limited resources, and in some instances the 287(g) program may not be a viable option," he says.

A less labor-intensive ICE program, Secure Communities, is more popular with police agencies. It is in use in 574 jurisdictions in 30 states. Under that program, everyone booked into a jail has fingerprints sent to the Department of Homeland Security to determine immigration status. Follow-through on illegal immigrants is done by ICE, not the local police.