A health clinic in this blue-collar city north of Oakland, partly funded by the county, is saving local hospitals thousands of dollars in emergency-room visits by treating uninsured patients who suffer only non-urgent ailments.

A watchdog group is now calling on county officials to cut funding for clinic patients who can't prove they are in the U.S. legally, a debate certain to surface in the national health-care overhaul.

With congressional proposals already stirring raw emotions, few supporters are eager to add the incendiary issue of illegal immigration. A provision in the House's health-care-overhaul bill rules out federal funding for illegal immigrants.

But in many ways, illegal immigration is at the nexus of two key health issues: the uninsured and ballooning costs.

Roughly half of the 12 million illegal immigrants in the U.S. don't have health insurance, according to the Pew Hispanic Center, a nonpartisan research group. Like others who can't afford medical care, illegal immigrants tend to flock to hospital emergency rooms, which, under a 1986 law, can't turn people away, even if they can't pay. Emergency-room visits, where treatment costs are much higher than in clinics, jumped 32% nationally between 1996 and 2006, the latest data available.

The role illegal immigrants play in U.S. health-care costs is "one hot button that no one wants to touch," says Stephen Zuckerman, an economist at the Urban Institute, a nonpartisan think tank in Washington.

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