After months of jaw-dropping predictions that the 2008 presidential election could cost $1 billion, the Federal Election Commission this week could put well-heeled Democratic and Republican White House candidates on the defensive as they decide whether to forgo public financing.

At its meeting Thursday, the FEC is expected to give Sen. Barack Obama (D-Ill.) permission to raise — but not spend — general election money for the presidential contest, which some campaign finance reformers argue should disqualify him from accepting the roughly $85 million in public money that would be available to the Democratic and Republican nominees.

But with scant opposition and no perceived advantages to either party, the agency’s six-member, bipartisan panel is expected to agree that Obama may take the money, provided that he keeps it in a separate account and gives it back to donors if he’s not still standing after the Democratic National Convention.

Assuming the commission votes in his favor, as expected, other White House candidates could feel the pressure to follow suit and raise money for the general election.

Already Obama and two rivals for the Democratic nomination, Sen. Hillary Rodham Clinton (N.Y.) and former Sen. John Edwards (N.C.), have opted out of the public financing system for the primaries, meaning they can exceed FEC spending limits that candidates who accept public funding must adhere to. Clinton also has signaled that she would not accept public money in the general election either — and the three leading candidates for the Republican nomination also are weighing whether to opt out.

“I think that it is not at all outside the realm of possibility” that 2008 presidential candidates still may use the public financing system during the general election, said Bob Bauer, Obama’s lawyer. “Once one candidate opens the door, other candidates are going to be either tempted or possibly under pressure.”

“Now you will have no excuse,” Bauer added. “Your opponent is prepared to do it. What’s the reason for turning that offer down?”

Republican election lawyer Cleta Mitchell speculated that Obama’s request is primarily about positioning himself against the fundraising prowess of Clinton, who is expected to raise $100 million this year.

“It’s posturing — mainly to make him seem like he’d really like to take the public money and stay within the public financing system, but because of circumstances he might not be able to,” Mitchell said. “I just can’t imagine how any serious candidate in a protracted presidential campaign can afford to take the public money.”

“Obama is trying to do what Hillary is doing [asking for general and primary money], but couch it and say that in some ‘I’d like to stay in the public system if I can,’” she added.

To stress her point that public financing simply is not an option, Mitchell pointed to all the states looking to front-load their presidential primaries in 2008. With both parties expected to have settled on their White House nominees by March 2008, she said, their campaigns could be running low on cash for the better part of six months before federal funds kick in.

“Let’s assume that all of these states move their primaries, so we really have presumptive nominees by this time next year,” Mitchell said. “The government money doesn’t come until after the formal nomination” in the late summer.

Still, the pressure to stay in the public financing system could be great. Assuming the agency sides with Obama, campaign finance reform groups are planning to ratchet up the pressure on presidential candidates to preserve the system.

“If the FEC approves the Obama advisory opinion request on Thursday, you can expect reform organizations to call on all presidential candidates to make a make a commitment that they will accept general election public financing if their major party opponent does so,” said Fred Wertheimer, president of Democracy 21. “If candidates do not accept public financing for the general election, this is going to end up as a $1 billion presidential race between the two major party opponents … beyond what anyone would have imagined even just a few years ago.”

He added: “The only way we are going avoid the $1 billion campaign for the two major party opponents is if an agreement is reached by both major party opponents to accept public financing in the general election.”

It may take a year or more for the repercussions of the FEC’s decision expected Thursday to be known, according to Paul Ryan of the Campaign Legal Center.

“It will be interesting to see come summer of 2008 if the Republican Party’s likely nominee chooses at that time to take Sen. Obama up on his offer to compete under the system of public financing,” Ryan said.

But if both candidates agree to opt in based on the agency’s presumed ruling Thursday, predictions of a $1 billion 2008 presidential election may short-lived, according to a Democratic-appointed FEC commissioner, Robert Lenhard.

“Assuming the candidates from both parties [would] follow this path, it could reduce the amount of money that they need to raise and would be able to spend in the general election,” he said.