But Obama's campaign, which has built what many political veterans believe is the best-organized presidential campaign ever, is also making a big push on early voting, which may help him put up a serious challenge for reliably GOP states such as North Carolina and Indiana.

He named North Carolina - a historically Republican state now considered a tossup - as one McCain's campaign would like to "put away" before Nov. 4. "We know who has the propensity to vote absentee, who we can push to vote absentee, who we want to do that," Beeson said.

"It's a turnout operation almost from Oct. 1 to Election Day, and you have to maintain that intensity and that focus," Beeson said.

Rich Beeson, political director for the Republican National Committee, said the GOP's voter-mobilization efforts used to concentrate on the 72 hours before elections. With the boom in early voting, he said, the party now makes a five-week-long push, during which they ensure supporters are registered and organize trips to voting locations.

Voters in several states, including those in the important battlegrounds of Iowa and Virginia, have already begun voting. Over the next few weeks, people in more than 30 states will join them. The shift toward early voting has enormous consequences for presidential campaigns, transforming the way they build turnout operations, allocate staff and money, and push messages in the media and in TV ads.

This year, some voting specialists believe that as many as one in three voters could have their decision banked before Nov. 4, compared with one in five who cast early ballots in 2004 and roughly one in seven who did so in 2000, according to Census surveys and Associated Press tallies.

"In many of these places, the polling place is a thing of the past," said Michael McDonald, a voting and elections specialist at George Mason University in Fairfax, Va.

The rush to vote early, abetted by the growing liberalization of state election laws, reflects a quiet revolution in American voting patterns that is reshaping the presidential race. The very notion of Election Day, when Americans gather in school gyms, community centers, and fire stations to pick a president, is slowly giving way to drawn-out election windows - weeks-long periods when voters, at their leisure, can cast ballots at designated spots or send them by mail.

For millions of voters over the next few weeks, the answer will be no. Confident in their choice of John McCain or Barack Obama, they will line up around the country to cast early ballots - at Albertsons grocery stores around Las Vegas, next to the Barnes & Noble at the Friendly Center shopping plaza in Greensboro, N.C., and in the student union at Drake University in Des Moines.

If you have already made up your mind in the presidential race, is there any point to waiting until Election Day to vote?

Yesterday, Obama's North Carolina campaign posted an Internet video of Obama, just before taking the stage at a rally in Greensboro on Saturday, urging supporters to vote as soon as the state's early-voting window begins, on Oct. 16.

"It can't be easier, but you've got to make the effort," Obama said, pointing backers to his campaign's sophisticated website, voteforchange.com, where they can register and find their early-voting locations.

Obama's national field director, Jon Carson, said the campaign is pushing early voting everywhere the law allows. But he named a number of battleground states where he said the campaign has made early voting a "major focus," including Nevada, New Mexico, North Carolina, and Indiana. He said that while the trend does not necessarily help one political party, it does help the best-run campaign.

"It favors the campaign that has the better organization and gets information into supporters' hands," Carson said.

Republicans and Democrats have been engaged in a fierce fight over early voting in Ohio, where, for the first time in a presidential election voters can cast ballots early with an excuse. From today through Monday, Ohio voters will be able to simultaneously register to vote and cast ballots, a window that Republicans argue disproportionately benefits Democrats. The Ohio Supreme Court and a federal judge yesterday rebuffed GOP-led legal challenges, allowing the early voting to proceed.

Voters who seek to preempt Election Day are driven by varying motivations: impatience, a desire to avoid crowds, schedules that make getting to the polls difficult.

"It takes a little bit of pressure off," said Lynn McRoberts, a 21-year-old political science major at Drake, who is helping McCain's campaign get students to an early-voting center at the student union on Oct. 15.

Others are simply tired of the all-consuming presidential race and want to check out early.

"They don't want to listen to the campaign anymore," said Matt Griffin, deputy secretary of state for elections in Nevada, where state officials expect at least half of voters to cast ballots before Election Day.

Despite the convenience voting early allows, one potential downside, some specialists say, is that it locks in one's vote before the presidential race has fully played itself out.

"Not only might you vote with less information that suddenly comes up at the end of the day, but you also will miss the debates, the scheduled things that you might want to see," said John Fortier, a political scientist at the American Enterprise Institute and the author of the 2006 book "Absentee and Early Voting: Trends, Promises, and Perils."

Election laws vary significantly across the country - from states with liberal laws such as Ohio, to Massachusetts, which requires absentee voters to have a reason for missing Election Day. (Only about 5 percent of Bay State voters voted absentee in 2004.) Two states that have moved the furthest from traditional Election Day voting are Oregon, which conducts elections by mail, and Washington, where 37 of 39 counties vote that way.

Interest in early and absentee voting has grown since the 1970s, especially in Western states, which have been the pioneers, researchers say. Researchers say that those who vote before Election Day tend to be the most partisan, unlikely to be swayed by a late debate, TV ad, or scandal, and that early voting has not favored either party.

With record turnout expected in a number of states, state election officials are actively encouraging voters to cast early ballots, because it lessens the demands on their offices on Election Day.

Colorado has been running public service announcements urging people to vote once the state's early-voting window opens Oct. 20. "It's a really strong message here," said Stephanie Cegielski, a legal specialist with the Colorado Secretary of State's office. "Get your vote in early."

Though Beeson acknowledges the strength of Obama's ground organization, he cautioned against drawing too many conclusions from the success either campaign has in getting supporters to cast early ballots over the next few weeks. He cited as an example New Mexico, where roughly half of voters cast early ballots in 2004.

In 2000, Beeson said, Republicans were more successful with early voters in New Mexico but ended up losing the state to Al Gore. Four years ago, he said, Democrats did a better job with early voting in the state but President Bush ended up beating Senator John F. Kerry.

Scott Helman can be reached at shelman@globe.com.

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