ATLANTA --- Sen. Saxby Chambliss, R-Ga., and Democratic challenger Jim Martin geared up Wednesday for a runoff even as state and county election officials continue to sift through ballots to see whether a second vote is necessary.

Some experts say it could take until Friday for all the results to be tallied. State officials must certify the election returns next week.

At a morning news conference at his campaign headquarters, Mr. Chambliss did not concede that he would fall short of the popular vote majority needed to avoid a runoff but said his campaign was preparing for one.

"We have already hit the ground," Mr. Chambliss said. "We have already organized for this runoff. ... We expect that, at the end of the four-week period, that we will maintain a strong lead."

Mr. Chambliss leads in figures supplied by the Secretary of State's Office, with 49.9 percent compared with Mr. Martin's 46.7 and Libertarian Allen Buckley's 3.4 percent. But Georgia law requires a runoff between the two top vote-getters when no candidate receives more than 50 percent.

The incumbent touted his lead as proof that he is well-positioned for any runoff and that Georgians would elect him now that the clutter of a hotly contested and attention-grabbing presidential race has been removed.

"I think folks now will have the opportunity to focus on one race, two candidates," Mr. Chambliss said.

Mr. Martin met with reporters at his headquarters as Mr. Chambliss held his news conference. Mr. Martin was certain there would be a runoff and said he had already invited Barack Obama to campaign on his behalf.

"We're going to win on Dec. 2 because this race is going to be about helping President-elect Barack Obama get our economy back on track and making the economy work for the middle class again," Mr. Martin said.

The Democrat is portraying his election as the completion of the Obama wave that swept the nation, discounting the fact that Georgia went for Republican Sen. John McCain.

Mr. Chambliss said he fully expects to see Mr. Obama try to influence the race on behalf of Mr. Martin.

"They're locked at the hip on raising taxes and putting more spending programs in place," he said.

But Mr. Chambliss said no decision has been made on whether to counter with President Bush or other national Republicans.

One thing Mr. Martin did predict was another round of negative ads.

"There are stark differences between me and Saxby Chambliss," he said. "We're going to talk about them, but we're not going to make personal attacks."

MEANWHILE, SUPPORTERS of Mr. Buckley, the third man in Tuesday's election, will likely be courted by Mr. Chambliss and Mr. Martin. Mr. Buckley hasn't made his position known, but in Sunday's statewide debate he said Mr. Martin is a good man but the wrong one to be senator and that Mr. Chambliss had been a terrible senator.

So far, counties have reported only 96 percent of their precincts. Many counties are treating votes cast in early voting on machines in person and by mail-in absentee ballots as additional precincts, making it difficult for state officials to know the number of votes remaining to be counted.

Some counties reported their early and absentee ballots shortly after polls closed at 7 p.m. Tuesday while other counties chose to tally those votes last.

Two other statewide runoffs were certain Tuesday, in the seven-person race for a vacant seat on the Court of Appeals, and for a vacant seat on the Public Service Commission. The runoff is Dec. 2.