About 20 percent of the 127,000-plus absentee ballots received as of early Friday were cast in three Indiana counties _ Marion, Monroe and Lake _ that political observers believe Obama is strongly favored to win.

Robert Dion, a professor of American politics at the University of Evansville, said Obama has mounted an innovative campaign that's stressed early voting and his supporters appear more energized than those for Clinton.

"In a close race, modest advantages in organization can yield big results, and if Obama out-organizes the Clinton campaign on these absentee ballots, it would be a great boost to him," Dion said.

Whatever Tuesday's final vote, Dion said Obama and Clinton are expected to basically split the state's 72 delegates.

"They're fighting over bragging rights," Dion said. "If he wins Indiana as well as North Carolina, which we expect him to win, he can say, 'I won both states.' And that's going to knock the wind out of Hillary Clinton."