COLUMBUS, Ohio — The campaign isn't over, but the voting is under way.

Before watching the presidential debates and without waiting for the next round of TV ads, millions of voters who have made up their minds about John McCain and Barack Obama will cast ballots before the Nov. 4 election day, thanks to expansive new early-voting laws.

In parts of Georgia, voting began last week. In Iowa, residents may vote at county auditor offices starting today. Early voting opens Tuesday in Ohio, a battleground state that McCain views as crucial to his chances.

"Some people now refer to October as election month," said Ryan Meerstein, director of the McCain campaign's Ohio operation.

More than 30 states have set up a mechanism for people to vote before Nov. 4.

About 14 percent of the electorate voted early in the 2000 campaign. That figure jumped to 20 percent in 2004, and this time around it could rise to more than 30 percent, according to Paul Gronke, head of the early voting information center at Reed College in Oregon.

Both presidential campaigns encourage early voting, particularly among people who tend to vote sporadically.

Over roughly a six-week period, the campaigns can target these voters with mailings, phone calls and personal visits in hopes of banking their vote. At McCain's local headquarters here last Saturday, about a dozen volunteers made phone calls to Franklin County voters, asking if they had received the absentee ballot application that the campaign has sent to about a million Ohioans.

"Early voting is one of the big phenomena this year," said Tad Devine, chief strategist for Democrat John F. Kerry's 2004 presidential bid. "This puts a premium on early organization. It affects where you send your candidate and when. It affects where you spend money on television times."

Obama aides are planning to lure people to vote early in Ohio by handing out concert tickets near the polling sites. The campaign is also considering taking college students to vote early by shuttle bus, with the promise of a happy hour event afterward.

One Obama aide said that in Ohio, the campaign is relying on turnout from students and blacks who have a "mixed record" of voting. Early voting gives the campaign more than a month to track these supporters and make sure they follow through and vote.