The decision to assign a small group of employees in the Maricopa County Attorney's and Sheriff's offices to immigrant smuggling cases is an unusual move for local authorities, given the long-held notion that immigration is the sole province of the federal government.

Some state politicians frustrated with Arizona's porous border with Mexico and the costs of illegal immigration say the federal government hasn't done enough to confront illegal border-crossings. They say Arizona, the nation's busiest illegal immigration corridor, must do what it can to lessen the problem.

The squads in the two Maricopa County agencies were set up, in part, to enforce a new law that creates the state crime of human smuggling.

Maricopa County Sheriff Joe Arpaio said his six-person unit will target immigrant smugglers, not the people who cross the border illegally merely to work.

''We don't go after the addicts on the street,'' Arpaio said, likening his immigrant smuggling crackdown plans with his office's approach in investigating drug cases. ''We go after the peddlers. Same philosophy.''

Local and state authorities have long pursued cases against immigrants who violate Arizona law, but in the past, they haven't been able to arrest smugglers, unless they committed state crimes.

Even so, state authorities have conducted financial investigations of people connected to smuggling operations, such as 21 employees of used-car lots who were charged last year with helping sell vehicles to smugglers.

The state also is working to establish a pilot project that would assign a dozen Arizona Department of Public Safety officers to assist local police and federal agents in immigration cases.

Like Arpaio, Maricopa County Attorney Andrew Thomas said his five-person squad hopes to not only put smugglers in jail, but also to reduce other crimes - murder, extortion, kidnapping - tied to illegal immigration.

''We will be able to have a multiplier effect,'' Thomas said.

Unlike Arpaio, however, Thomas' spokeswoman Krystal Garza said the prosecutor's office is considering whether to charge as co-conspirators illegal immigrants who sneak into the country for the purpose of working.

Arizona has been dogged by a heavy flow of illegal immigrants since the government tightened enforcement in El Paso, Texas, and San Diego during the mid-1990s.

While immigrants provide the economy with cheap labor, Arizona shoulders huge health care and education costs for illegal workers and their families.

Political pressure for the state to confront illegal immigration began mounting last year when voters approved a law that denied some government benefits to illegals.

It continued when state lawmakers gave local and state police the power to arrest immigrant smugglers. The new law, which takes effect Aug. 12, also aims to confront the problem of immigrants and others being forced into labor or prostitution.

The Legislature didn't provide any additional money for police to enforce the law. Some officials have said the law will be of limited use because they don't have the time or money to build cases against smugglers.

Santa Cruz County Attorney George Silva, whose jurisdiction includes 50 miles of the U.S.-Mexico border, said federal agents are still in the best position to arrest smugglers. His office has a $900,000 budget and eight attorneys to prosecute criminal cases.

''It's awesome that Andrew [Thomas] can open up a unit, but I can't afford it,'' said Silva, who will consider using the new law on a case-by-case basis if federal authorities can't prosecute smuggling cases.