OTTUMWA — It wasn’t a surprise when presidential candidate Fred Thompson took a swipe at fellow candidate Mitt Romney recently over immigration. Candidates for president want to show voters how they differ from rivals, and immigration is shaping up to be one of the biggest issues of the campaign.

Immigration is back as a political fight, and it’s spilling over into communities around the country. Groups rarely agree on just how big an issue it is. The U.S. Census Bureau’s 2006 estimate indicated there are 37.5 million foreign-born residents in the country. About a third of them have arrived since 2000. The vast majority, 20 million, are from Latin America.

There’s a catch, though. The bureau doesn’t ask whether people came to the country legally. Even those who favor wholesale deportation of illegal immigrants don’t generally support closing the borders entirely. So the fight over immigration often morphs into a debate over illegal immigration and what to do with illegal immigrants who are already here.

How many immigrants are here illegally depends on who you ask. The Center for Immigration Studies puts the figure at 8-10 million. Tom Tancredo, whose presidential campaign relies heavily on illegal immigration as a rallying point, says there are at least 12 million illegal immigrants. Other estimates go as high as 38 million.

There are no good estimates for Ottumwa. Most estimates put Wapello County’s immigrant population at 3,000-4,000. But that does not distinguish between legal and illegal immigrants.

The debate in Ottumwa tends to simmer rather than explode. There are flashpoints, but it lies beneath the surface for the most part. The biggest eruption so far was the January 2007 debate over whether to apply for the ICE 287(g) program.

Law enforcement works in a stratified atmosphere. Agencies have specific areas of responsibility. And it’s not always possible for law enforcement authorized in one jurisdiction to function in the same capacity elsewhere. City police officers can’t generally enforce federal law.

ICE, the Immigration and Customs Enforcement agency, developed the program to bring local law enforcement into immigration enforcement. The program trains local officers on how to begin deportation proceedings when an illegal immigrant is arrested. They remain officers at their local departments, but can function in a limited capacity as federal agents.

Ottumwa Police Chief Jim Clark, then the interim chief, brought the program to the city council’s attention. He said the program can target violent offenders in Ottumwa and remove them from the community.

Not everyone bought it. Latinos Unidos claimed the program would promote fear of law enforcement within the Hispanic community. Norma Rosales predicted Ottumwa would “become a ghost town,” if the city joined the program.

Clark says he tried to work with the Latino community to emphasize that the program was not designed to target a large group. The Ottumwa plan was to go after people who commit violent crimes, usually felonies. The accretion of an extensive police record alone would not trigger deportation proceedings, provided the record was comprised of misdemeanors.

It does not appear that the message got across. Himar Hernandez, formerly the director of the New Iowans Center in Ottumwa, said Clark failed to include the Latino community in the preliminary discussions about the program.

“The problem here was not the program, it was how it was communicated to the Latino community,” he said. “We knew there was no money from the start.”

Ottumwa eventually applied, but it does not look like the program will go into effect here. Clark announced late this summer that ICE officials told him Congress allocated enough money for only three new cities and that they wanted to focus on large cities and border areas.

Beyond specific flashpoints, much of the debate over immigration focuses on two basic issues: culture and social services. Clark says immigration is playing a role in stretching Ottumwa’s social services, particularly for law enforcement. It’s not that immigrants are more prone to breaking the law, he said, it’s that population growth brings more opportunities for any conflict.