Since the home-invasion killings of six Mexican workers last fall, police in this south Georgia town have tried to win the trust of thousands of immigrants who come to pick peanuts, peaches and cotton in the rolling fields.

But Chief Jim Smith's efforts have run up against a new reality — increased pressure on local police to help enforce immigration laws, fueling fears among immigrants that even a small run-in with officers could result in deportation.

"If they think we're INS, we'll never gain their trust," Smith said, referring to the former name for the federal immigration enforcement agency. "We work real hard to gain their trust and don't want to jeopardize that if we can."

Some federal officials say they need at least some of the nation's more than 660,000 police officers and sheriff's deputies to help crack down on illegal immigrants, especially those who are convicted criminals.

"Immigration and Customs Enforcement is vastly undermanned right now. It's not able to effectively scan the whole country," said Kris Kobach, a former counsel to the U.S. attorney general who worked on several local-federal immigration partnerships. "You've got 2,000 people whose full-time responsibility is to look for those 11 to 12 million [illegal immigrants]. Even if a very small proportion of officers help only passively, that's a huge help."

But Smith is among the local police officials worried that their ability to fight violent crime will be affected. Four people have been arrested in the Tifton slayings and authorities believe others in the area are committing similar crimes, preying on illegal immigrants who sometimes carry lots of cash because they lack bank accounts.

Smith has stepped up patrols in the trailer parks where most immigrants live, worked to recruit Spanish-speaking officers and given others cheat sheets with basic phrases in Spanish. But he also must contend with a new state immigration law that is considered one of the nation's toughest.

The law requires local officers to check the immigration status of anyone arrested for a felony or drunken driving. It also makes Georgia the first state directed by law to enter into an agreement with the federal government to train local officers so they can start the deportation process for any illegal immigrants found during normal law enforcement activities, like traffic stops or drug busts.

Congress and at least 14 other states have been working on similar legislation, according to the National Conference of State Legislatures.

Since 1996, the federal government has offered immigration-enforcement training to police and sheriff's agencies, but relatively few officers have gone through the program. The first — 60 members of the Florida Department of Law Enforcement — didn't get trained until 2002.

Sheriff Mike Carona of Orange County, Calif., wants to train 500 of his deputies, which would be the largest use of the program to date. Costa Mesa, in that county, will become the nation's first city to enter the agreement if it goes forward with training its jailers, police detectives and gang units as proposed.

Other sheriffs and police chiefs have resisted more authority. Their resources are already strained, their jails are already full and any further alienation with their immigrant communities will reduce their ability to fight underreported crimes like domestic and sexual violence, said Gene Voegtlin, legislative counsel of the International Association of Chiefs of Police.

"I don't think any of us delight in the process of becoming immigration officers," said Cochise County Sheriff Larry Dever, who oversees 85 officers patrolling 6,300 square miles in Arizona's southeastern corner, an area that consistently leads the nation in immigration arrests.

Citing police opposition, Arizona Gov. Janet Napolitano vetoed legislation last month that would have let local authorities arrest illegal immigrants anywhere in the state. Other legislation, however, is being used for the same purpose.

The sheriff of Maricopa County, which includes Phoenix, has organized a 100-member posse to arrest illegal immigrants, using a new Arizona law that the county attorney contends allows them to be prosecuted for conspiring to smuggle themselves into the country. The law's authors, however, say it's aimed at immigrant smugglers, not the immigrants themselves.

In the Midwest, where federal immigration agents are much more scarce, the cities of Minneapolis and St. Paul, Minn., have ordinances barring police from asking about immigration status if they're shown a valid foreign or state identification like a passport or driver's license. Their police departments oppose a push by Gov. Tim Pawlenty to overturn those policies.

Alabama state troopers, meanwhile, have made more than 160 immigration arrests since receiving federal training in 2003, including that of a convicted sex offender as he applied for a driver's license.

Troopers verify the status of everybody they come into contact with, said Alabama Department of Public Safety spokeswoman Martha Earnhardt.

That worries some advocacy groups, who fear victims and witnesses of crimes won't come forward if their papers aren't in order, said Michele Waslin of the National Council of La Raza.

Immigration officials, however, emphasize that their top priority is arresting those who threaten public safety, not rounding up all illegal immigrants.

"ICE agents can't be everywhere," Immigration and Customs Enforcement spokesman Mike Gilhooly said. "We're after people who are criminals, who are breaking serious laws. Even in immigrant communities, they don't want a child molester living in a community where people are trying to live the American dream."