Florida election supervisors are reacting warily to a statewide effort to cleanse the rolls of non-citizens, warning that inaccurate or obsolete data could lead them to disenfranchise eligible voters.

State election officials recently told county supervisors that they had identified as many as 182,000 voters who were on the rolls despite not being eligible to vote, but a list they disseminated with the names of 2,600 voters was rife with errors, supervisors say.

That has supervisors worried about a repeat of 2000, when an effort to expunge disqualified felons from the rolls led to eligible voters being mistakenly turned away from voting. Some have credited the blunder with helping President George W. Bush narrowly win Florida, and the presidency, in a bitterly contested election whose results many critics still dispute. A perennial battleground state, Florida could again prove pivotal in what seems likely to be a close race between President Obama and Mitt Romney.

That [in 2000] was a very similar situation where that first list that came down to us was very, very inaccurate, Susan Gill, supervisor of elections for Citrus County and a 16-year veteran, said. And so those of us who have been around for a while, that's why we're extremely skeptical and walking very carefully on this because we don't want to go through that again.

Florida has made strides since then, Gill said, although she noted the process has not been without pain. The Florida Voter Registration System, launched in 2006, allowed election monitors to cross-reference information with the Department of Health in order to identify deceased Floridians still registered to vote. A controversial new law tightening voter registration requirements has expanded that process, allowing the state to cross-check voter rolls against Social Security data and producing a list of 53,000 additional dead voters.

I feel very confident in the integrity of that list because I think we have some good data matches there, Gill said.

But Gill and her colleagues are less sure about the state's information relating to citizenship -- two of three Citrus County residents identified on the state's list were in fact citizens, a lapse Gill attributed to a data mismatch.

Florida has moved to rectify the situation by comparing their list of allegedly ineligible voters against a federal Department of Homeland Security database. Florida's Department of State had unsuccessfully sought access to the federal database, but its Department of Highway Safety and Motor Vehicles already had the ability to reference the database.

It was my understanding that that database has the most up-to-date immigrant information anywhere, so we're pretty confident that we will get a more accurate list, said Susan Bucher, Palm Beach County's supervisor of elections. We need that, because we know there are errors already before we begin.

Bucher said state election officials had reassured them that there are always errors, you can add them back if people were wrongfully knocked off the voter rolls, something she called a little disturbing.

There's no need to interrupt or disrupt voters who are completely eligible just because we didn't do a good job of getting accurate or updated information, Bucher said.

Ensuring that voting records are up-to-date and precise is not an easy task. A recent study found that some 24 million U.S. voter registrations, or about one in eight, are flawed. The most common reasons were people dying or moving without notifying election officials or records containing misspelled names or incorrect addresses. When non-citizens do appear on the rolls, Gill said, it can be because of simple oversights like immigrants unknowingly filling out registration forms when applying for driver licenses.

Because it is so difficult to guarantee the integrity of a sprawling and ever-changing system like a voter database, Florida's efforts to purge non-U.S. citizens pose serious risks, according to American Civil Liberties Union of Florida communications director Derek Newton.

Is it better to check more sources? Of course, Newton said. But government databases are never entirely accurate. It doesn't matter whether you're talking about the Social Security rolls or the no-fly list or the Department of Motor Vehicles. Massive government databases are going to have errors.

People who should not be registered should not be registered, but this process seems excessive and unwarranted, Newton added.

The push to validate Florida's rolls also shifts the burden of proof from election officials proving that voters are ineligible to registered voters needing to offer proof of their citizenship, Newton said.

If the supervisors or election officials can prove someone has registered improperly or are voting improperly, there are already procedures in place to stop that and punish that, Newton said. So it raises the question: What is the point of this exercise we know is flawed, especially considering it's based on data we know is wrong.

Polk County elections supervisor Lori Edwards had a similar criticism, saying the Department of Elections had turned this into a removal process by having her demand that people produce documentation.

Edwards is already deeply skeptical, noting that four of the 21 Polk County residents the state identified as non-citizens listed Puerto Rico - a U.S. territory whose residents are automatically granted citizenship -- as their country of origin. Her chief deputy's father, a naturalized citizen who years ago emigrated to the United States from England, was listed as a non-citizen before her office caught the mistake.

Ultimately, it falls to election supervisors to decide whether to strike a voter from the rolls, and Edwards said that she planned to have her staff perform multiple follow-up contacts after initially sending letters asking that potentially ineligible voters provide proof of citizenship. While she agreed with the need to keep the voter rolls up-to-date, Edwards questioned the state's timing.

I think there is a need to make every effort to see to it that our voter rolls are as clean and accurate and fraud-free as possible, Edwards said. I'm not sure there's a need for a big haphazard slapdash rush right before a presidential election.