-- An estimated 153.1 million Americans have registered to vote, an increase of 10.1 million that sets the stage for a likely large turnout on Election Day, a non-partisan study reported Sunday.
American University's Center for the Study of the American Electorate estimated 73.5% of citizens 18 or older have registered, compared with the previous high of 72.1% set in 1964.
Curtis Gans, director of the center, said that the registration gains "could lead to a turnout of as many as 135 million" voters or about 65% of eligible citizens. That would be the highest since 67% of citizens 18 and over voted in 1960, he said.
Democrats gained an estimated 2.9 million new voters, while Republican registration declined by about 1.5 million, the report said. The study estimated those figures based on registration in 19 of the 28 states and the District of Columbia that register voters by party.
The report said the GOP decline was small but significant "in this year of intense citizen interest in the election."
Democratic registration increased the most in Nevada, Pennsylvania and Colorado, all battleground states, and Arizona, a late-emerging battleground. Republican registration declined in Colorado, Florida and Pennsylvania but increased in Nevada, the report said.
Signs of strong voter interest have been seen in early voting in some of the potential swing states where both candidates have focused attention.
In North Carolina, nearly 2.6 million people — more than 40% of registered voters — have already cast a ballot. That is more than double the 1.1 million early voters in 2004. State Board of Elections figures show that 52% of those who voted are registered Democrats, and 30% are registered Republicans. Democrats make up about half of all registered voters in North Carolina, which last voted for a Democratic president in 1976.
Early voting has required patience as lines were long in many cases. In North Carolina, elections officials permitted counties to extend voting hours by four hours on Saturday.
In Georgia, the secretary of State's office said nearly 2 million people, or 35% of registered voters, have cast votes early, outstripping predictions and causing some voters to stand in line until late at night.
Indiana, a traditionally Republican state where Democrats have an intense effort, elections officials said more than 10% of the 4.5 million registered voters cast early ballots. Polls in Indiana show Republican John McCain and Democrat Barack Obama essentially tied.
Ohio, a focus for both Obama and McCain, at least 1.5 million people will have cast ballots before Tuesday, elections officials estimate.
In Colorado, the secretary of State's office said 1.8 million people voted before the Friday deadline for early voting.
In Nevada, more than 600,000 early and absentee ballots have been cast, a heavier-than-expected figure that prompted state officials to increase their turnout predictions. They now say 1.1 million of the 1.4 million registered are expected to vote.
Contributing: The Associated Press