As Mayor Bloomberg eyes a run for president, candidates from both parties are likely eyeing him — and his billions of dollars — for the no. 2 spot on a ticket.

It is expected Mr. Bloomberg could spend as much as $1 billion on a presidential campaign if he runs, but his personal fortune could also be used to help propel another candidate to the Oval Office — if Mr. Bloomberg were to open his wallet to support a ticket on which he’s the vice presidential candidate.

Such a scenario would be unprecedented, campaign finance experts say, noting that while presidential candidates have given millions of their own dollars to support campaigns, there hasn’t been a case where a vice presidential nominee has bankrolled a White House run.

Mr. Bloomberg’s associates say he is unlikely to join a ticket in the no. 2 slot, but some observers argue that being vice president would allow him to stay in the national spotlight and spearhead initiatives in areas he has focused on as mayor, including the environment and public health.

While the mayor has indicated he wouldn’t be interested in serving as vice president, he’s also denied that he is a candidate for president, publicly pushing back efforts by his aides to keep the notion alive.

“I’m a little bit too old to work for somebody else,” he said in December, when asked about the second spot at the White House.

A former aide and campaign strategist to the mayor, William Cunningham, said he doubted Mr. Bloomberg would spend his personal fortune to send another candidate the White House, even if he was on the ticket.

“I just don’t think he’d take out his wallet or his credit card or his checkbook to pay for second place,” he said. Mr. Cunningham added that if the mayor did run as vice president but kept his money away from the campaign, he thought it would be fun “to watch him go to all those fund-raisers.”

Mr. Bloomberg is mentioned as a possible vice presidential nominee on tickets with Republican and Democratic candidates.

A breakfast at a Midtown Manhattan diner in November set off a torrent of speculation that an Obama-Bloomberg ticket could surface this year, and talk of a possible partnership between Senator McCain and Mr. Bloomberg began when the Republican candidate praised the mayor’s record on education during a debate on December 12.

A former opinion columnist for the New York Times, William Safire, predicted in a piece that ran in the Times on December 31 that Messrs. McCain and Bloomberg would team up.

A spokesman for the Federal Election Commission, Robert Biersack, said that if a vice presidential candidate tried to bankroll a ticket, it would put the campaign in uncharted territory.

Mr. Biersack said that while there’s no restriction on how much personal money presidential candidates can spend on a campaign, so long as they do not accept public funds, federal campaign finance laws don’t specifically address what that means for a vice presidential candidate.

“We’ve never had a vice presidential candidate who was in that position,” he said.

Election lawyers, however, said a presidential campaign financed by a vice presidential candidate would be on sound legal ground.
In recent primaries, presidential candidates have loaned themselves large sums. Senator Kerry put up $6.4 million of his own money for his campaign, according to the FEC, and Governor Romney has given his campaign about $17 million.

A professor of political science at Baruch College, Douglas Muzzio, said he thought Mr. Bloomberg’s fortune might be his most appealing attribute as a vice presidential candidate.

A report on Wednesday indicated Mr. Bloomberg isn’t ready to start looking at vice presidential posts any time soon. He is conducting extensive polling and voter analysis in all 50 states in preparation for a possible White House bid, according to the Associated Press. Adding to momentum behind a possible campaign by Mr. Bloomberg is a report that a political organization working to nominate a third-party presidential ticket, Unity08, is making plans to largely shutter its operation to focus on the mayor’s potential campaign.

According to a letter from leaders of the organization to its members posted on the New York Observer’s political Web log, the Politicker, two of the group’s leaders are leaving to join a committee forming to draft Mr. Bloomberg, “should the circumstances seem right.”

“At the current moment, we don’t have enough members or enough money to take the next necessary step — achieving ballot access in 50 states — to reach the goal of establishing our on-line convention and nominating a Unity ticket for president and vice president this coming fall,” the letter says.