AUGUSTA — Supporters of same-day voter registration are touting a report by a think tank that analyzed the potential effect of new laws passed by more than a dozen states — including Maine — to change how and when voters can register and vote.

The Brennan Center for Justice at the New York University School of Law, which focuses on voting rights, redistricting and campaign finance reform, issued its report Monday. It concludes that the laws, adopted largely by new Republican majorities in state legislatures, “could make it significantly harder for more than five million eligible voters to cast ballots in 2012.”

The Brennan Center used records of how many people registered or voted under now-banned methods to reach its conclusions. For example, because about 55,000 Mainers registered to vote on Election Day in 2008 or the two business days before it — something that would be prevented by a law passed in June — the study counted them in the estimate.

“This wave of changes may sharply tilt the political terrain for the 2012 election,” the report said, but “it is too early to quantify how the changes will impact voter turnout.”

The report was highlighted in a news release by the Yes on 1/Protect Maine Votes campaign, which hopes to convince Mainers to overturn the law to eliminate same-day registration.

The law’s fate will be determined in a statewide referendum Nov. 8. it cannot take effect while the vote is pending.

“Reputable research confirms what we already know in Maine. Same-day registration works,” said Sarah Walton, a member of the League of Women Voters of Maine and an assistant professor of justice studies at the University of Maine at Augusta, in a news release.

Yes on 1 supporters have argued that repealing Maine’s 38-year-old law allowing same-day registration would disenfranchise some voters, particularly students, the elderly and people who are disabled.

Lawmakers who led the repeal effort and their supporters say the change is needed to give municipal clerks more time to process and verify information provided by new registrants. They argue that some voters’ unfair exploitation of the law in 2008 doesn’t mean that none of them would have voted without the provision.

Lance Dutson, chief executive officer of the Maine Heritage Policy Center, the only group to register with the state to oppose the Yes on 1 people’s veto initiative, dismissed the report’s findings.

“I guess what they are saying is that fraud never happens, so we don’t need any checks in our system,” he said. “In the absence of a process or structure to check the validity of registrations, clerks need time to manually verify them. If we had photo ID and a usable central voter registry, Election Day registration wouldn’t leave the door open to problems the way it does now.”

Dutson said his concerns are justified by an investigation by Secretary of State Charlie Summers, who found six non-U.S. citizens on the voting rolls among about 500 voters who were scrutinized and an 84 percent error rate in registration filings.

Summers has said the errors included clerks checking off wrong names on voting lists and registrants failing to fill out all of the appropriate information on the registration cards.

The first campaign finance reports for groups that are raising and spending money on the referendum are due at the end of Wednesday. Seven groups have registered in support of the repeal effort.

Rebekah Metzler — 620-7016

rmetzler@mainetoday.com