Newt Gingrich’s immigration proposal, which would give special consideration to illegal immigrants who have lived here for many years and have deep ties to their communities, has the potential to affect millions of illegal people, according to a new study.

But the plan, which some political observers thought would alienate conservative voters, hasn’t hurt Gingrich’s front-running campaign for president.

A month before voting starts, Gingrich has established double-digit leads in some polls in the early voting states of Iowa and South Carolina. He leads former Massachusetts Gov. Mitt Romney, who has a deeper war chest and a bigger campaign operation, 38 percent to 22 percent in South Carolina, according to a Winthrop University poll released Tuesday. A Washington Post-ABC News poll, also released Tuesday, gives Gingrich a 33 percent to 18 percent lead in Iowa over Romney and Texas Rep. Ron Paul.

Gingrich, a former Georgia congressman and U.S. House speaker, hasn’t fully fleshed out his plan or set a minimum number of years for how long illegal immigrants must live here before they could be eligible for a path to legal status.

One new estimate says there are 3.5 million illegal immigrants who have lived in the United States for 15 years or more.

Gingrich’s opponents in the race for the GOP nomination — including U.S. Rep. Michele Bachmann of Minnesota and Romney — have dismissed his idea as a form of amnesty. Gingrich called his proposal a “humane” way to deal with a vexing problem.

The proposal might even help Gingrich should he win the nomination by broadening his appeal among Hispanic voters, said Merle Black, an Emory University political scientist. But there is still a chance he also could alienate people within his own party, he said.

“It certainly separates him from some of the other Republican candidates,” said Black, who has written about presidential politics. On the other hand, Black said, “a lot of his potential supporters may have been taken off guard by his position on this issue because they tend to take a more hard-line view of this.”

Gingrich’s proposal is dividing his supporters in Georgia, who hold strong views on the red-hot button issue. For example, a spokesman for Republican Gov. Nathan Deal — Gingrich’s Georgia campaign chairman — confirmed this week that while the governor still supports Gingrich, Deal opposes granting amnesty to illegal immigrants regardless of how long they have lived here.

Gingrich unveiled his plans last month when he said a path to legal status should exist for illegal immigrants who have lived here for 20 or 25 years, obeyed the law, paid taxes, gotten married and had children. Those people would have to pass a criminal background check and go before citizens review committees for consideration, Gingrich proposed. Those panels would consider their family and community ties and their ability to support themselves without government entitlement programs.

Applicants who are allowed to stay in the United States would have to pay a fine of at least $5,000, learn English and prove they can pay for private health insurance. They would not automatically be given citizenship under this scenario but would have to apply for it separately, Gingrich said.

Asked about the sketchiness of Gingrich’s proposal, a spokesman for his campaign said Gingrich’s aim is to outline the idea publicly and listen for feedback to improve it. His spokesman, R.C. Hammond, said the proposal will be fleshed out as part of that process.

“It is all part of the conversation,” Hammond said.

After Gingrich first mentioned his idea on the campaign trail last month, the Pew Hispanic Center — a nonpartisan research organization based in Washington — set to work studying the potential impacts. Beyond the 3.5 million adult illegal immigrants who have lived here 15 years or more, there are 2.8 million more who have lived here between 10 years and 14 years, Pew reports.

The center did not have the information it needed to estimate how many illegal immigrants are not committing additional crimes here and paying taxes, said Jeffrey Passel, a senior demographer for the center.

For Gingrich supporters, the proposal has put them in the position of supporting the candidate but opposing the immigration plan.

Republican U.S. Rep. Phil Gingrey of Marietta is “staunchly opposed to amnesty in any form and believes that we can make substantial progress by enforcing existing immigration laws,” according to his spokeswoman. But Gingrey still supports Gingrich.

In contrast, Republican state Rep. Joe Wilkinson of Sandy Springs, one of Gingrich’s longtime friends, supports his immigration proposal, saying it could help American farmers who need legal workers. Farmers in Georgia have complained the state’s new immigration law — House Bill 87 — has scared away the migrant Hispanic workers they depend on, leading to substantial crop losses.

“What Newt proposes is certainly not a cakewalk to legal status or citizenship by any means, but it should appeal to one’s sense of fair play,” he said. “It is tough but fair.”