LITHONIA, Ga.  Just a few blocks off Max Cleland Boulevard, named for the Democrat defeated by Senator Saxby Chambliss in a bitter Congressional race six years ago, a line has formed that could be problematic for Mr. Chambliss’s own re-election this year.

Hundreds of voters, most of them black residents of bedroom communities east of Atlanta, are waiting to cast early ballots, motivated by the candidacy of Senator Barack Obama but many also taking the opportunity to vote for Jim Martin, Mr. Chambliss’s Democratic opponent.

“I voted for Jim because I like what he is saying, not just because he is Democratic,” Iris Epps said as she exited Lithonia Middle School after waiting about 90 minutes on Tuesday evening to cast her ballot. She said the wait would have been even longer earlier in the day.

Like several other Senate and House candidates in North Carolina, Ohio and Connecticut, Mr. Chambliss finds himself in a tight race even though only months ago he was considered a cinch for re-election. A significant part of his problem is the surging participation by African-American voters, their ranks bolstered by the newly registered, a group expected to vote overwhelmingly for Democrats this year.