Mayor Bloomberg, who could enter the presidential race as early as next month, is defending himself against President Clinton’s claim that Mr. Bloomberg’s ability to spend his own multibillion-dollar fortune would give him an unfair advantage.

“I don’t think it’s that big a problem.” Mr. Bloomberg said of self-financed campaigns yesterday. “And the public certainly knows about the fact that I’ve made my own money, spent my own money, and they’ve seen that at least twice when they’ve gone into the polling booth and said that’s not an issue.”

Mr. Clinton was quoted in the online publication Politico as telling a crowd in Iowa on Sunday that self-financed campaigns “violate the spirit of campaign finance reform.” Mr. Clinton said that the Supreme Court, which has ruled that spending money on one’s own campaign is a constitutional right, “seems determined to say that the wealthier have more right to free speech than the rest of us.” He mentioned Mr. Bloomberg several times directly, saying that while he admires the mayor, he is upset with his potential ability to employ his personal fortune in a presidential campaign.

While Mayor Bloomberg’s unique ability to self-finance a presidential campaign makes him a viable independent candidate, Mr. Clinton’s comments suggest that Mr. Bloomberg’s advantage may become a liability as well. The exchange could foreshadow similar attacks against the mayor should he leap into the race, possibly facing off against Mr. Clinton’s wife, Senator Clinton. With the Iowa caucuses on January 3, a likely decisive assortment of state primaries on February 5, and state deadlines for petitioning to be on the ballot looming in the spring, Mr. Bloomberg will have to decide soon whether or not to run, lending the question of how to handle public perceptions of his wealth greater immediacy.

Mr. Bloomberg’s vigorous defense of self-financing seems to indicate that he is prepared to parry attacks by spinning his money as a positive factor. Yesterday he said that self-financing had allowed him to avoid having to reward big donors with special favors and patronage positions.

“I would never have been elected had I had to go out and solicit contributions. I also wouldn’t have been as free to appoint the best people if I had solicited contributions,” Mr. Bloomberg said at a firehouse in Brooklyn. “Nobody makes contributions without expecting something. Small donors probably just expect good government — and let’s hope they get it — and big donors sometimes, as we all know, expect appointments or favorable legislation.”

Mr. Bloomberg, while emphasizing the positive aspects of self-financing, also minimized its impact on the election results.

“I think one of things that you can take comfort in if you’re worried about people buying elections, is that statistics show that wealthy people who self-finance don’t win with any greater frequency than those who have to go out and raise money from others,” Mr. Bloomberg said.

“The election results speak for themselves,” a spokesperson for Mr. Bloomberg, Stuart Loeser, added yesterday, supporting the mayor’s assertion that wealth alone cannot guarantee electoral success. “Some candidates spend more of their own money and get fewer votes, as Michael Huffington and Blair Hull did, and some get more votes, as Jon Corzine and the mayor did.”

Mr. Hull, an Illinois Democrat, spent millions in 2004 Senate primary, only to lose to Senator Obama, while Mr. Huffington, a California Republican congressman, self-financed an unsuccessful run against Senator Feinstein in 1994. Mr. Corzine won a Senate seat in 2000 and then the governorship of New Jersey in 2006 in two self-financed campaigns. In New York politics, billionaire Thomas Golisano spent tens of millions in three losing campaigns for governor with the Independence Party.

Mr. Bloomberg would not be the first presidential candidate to rely on a personal fortune to power his run. Steve Forbes sank a total of $69 million into his 1996 and 2000 presidential campaigns, according to the New York Times, only to be defeated in the Republican primaries by Senator Robert Dole and George W. Bush, respectively. Texas billionaire Ross Perot spent an even larger amount, $71 million, on his third-party runs in 1992 and 1996. In June 1992, a Time-CNN poll showed Mr. Perot leading his opponents, President Clinton and President George H.W. Bush, by 13 points, but he ultimately failed to win a single electoral vote, despite strong showings in several states.

Mr. Bloomberg’s potential campaign, however, would likely operate on a scale far greater those candidates, making comparisons difficult. In his two mayoral campaigns, Mr. Bloomberg spent a total of about $150 million, eclipsing Mr. Perot and Mr. Forbes’s combined spending on four presidential campaigns. A close adviser to Mr. Bloomberg, Kevin Sheekey, was quoted in Newsweek in November as saying that any presidential run by the mayor would be “a billion-dollar campaign.”