With 99 percent of precincts reporting Wednesday, Chambliss had 49.8 percent of the vote, short of the 50 percent plus one required under state law to avoid a runoff. Democrat Jim Martin, a former Georgia legislator and once-reluctant Senate candidate, won 46.8 percent of the vote. Libertarian Allen Buckley pulled 3.4 percent.

Some absentee votes still were being counted late Wednesday. However, if the current results hold, Chambliss would face Martin in the runoff.

Chambliss, in a conference call with state reporters, said it likely will be this weekend before the final tally will be known in his re-election bid.

"We had a topsy-turvy night in terms of the vote," Chambliss said. "Right now, we have 49.99 percent of the vote, but as of this morning we are in full runoff mode," he said.

Chambliss differs with his Democratic opponent on the number of ballots outstanding, saying there are "only a few thousand." He said that if he had an additional 4,000 votes, the race would be over.

Chambliss said while it is early, the campaign plans to invite surrogates to campaign for him, mentioning Sen. John McCain and Alaska Gov. Sarah Palin, who lost the presidential race. Others named included former New York Mayor Rudolph Giuliani, former Arkansas Gov. Mike Huckabee and former Massachusetts Gov. Mitt Romney.

Earlier Wednesday, Martin told a telephone news conference that he was confident he would be in a runoff with Chambliss, a Moultrie Republican.

"We’re in a runoff," Martin said, adding that his campaign staff believes there are about 200,000 ballots, mostly absentee, that have not been counted and most of those will fall to him.

He predicted it would be next week before the election results are certified, officially setting up the runoff.

Martin said his campaign has been in contact with the campaign staff of President-elect Barack Obama, but said it was too early to say if Obama would be coming to Georgia to campaign for him.

In Hall County, Chambliss topped Martin by a vote of 39,502 to 15,231 in incomplete returns.

Under Georgia law, a general election candidate must receive more than 50 percent of the vote.

The law was changed to 45 percent by Democrats in 1993 after the 1992 loss by U.S. Sen. Wyche Fowler, D-Ga., in a runoff to Republican Paul Coverdell. Republicans in the General Assembly restored the 50 percent law in 2006.

Chambliss in a runoff is similar to the situation Fowler had in 1992. The incumbent Democrat was the top vote getter with 49.23 percent on Election Day, however Libertarian Jim Hudson received 3 percent of the vote, setting up a runoff two days before Thanksgiving with Republican Paul Coverdell, who won in the second round of balloting.

Bill Clinton, who had just been elected to his first term as president, came to Georgia to campaign for Fowler.

If Obama gets involved, it would be the first test of whether the president-elect can mobilize voters when he is not on the ballot. On Tuesday, Democrats added three seats to their Senate majority, but even if they swept the remaining still undecided races, they would fall short of the filibuster-proof, 60-vote majority.