Mayor Bloomberg, no longer a potential presidential contender, said today that the candidates are starting to reflect his brand of bipartisanship and that his endorsement — which could come with a hefty financial boost — is up for grabs.

The billionaire mayor, who is friendly with Senator McCain as well as Senators Clinton and Obama, finally put to rest more than two years of speculation that he would launch his own independent bid for the White House. He said he had thought “long and hard” about whether to run.

“The candidates that are emerging, I think in all fairness, are showing some hopeful signs of understanding the need for independent leadership,” Mr. Bloomberg told reporters. “And I believe that the most productive role I can play is to continue pushing them in that direction.”

Mr. Bloomberg spoke after penning an op-ed piece that appeared in today’s New York Times, pledging unequivocally that he would not run this year but dangling another juicy tidbit that is sure to keep him in the spotlight as the race chugs on without him: He might throw his wealth and support toward one of the campaigns.

At an afternoon news conference, Mr. Bloomberg was asked what a candidate might have to do to win his endorsement, and he began by saying “they’re all in contention.”

He said he is looking for the candidate who does not work along party lines, addresses the intricacies of issues and has thought ahead to the legislative process and how to finance specific programs. He said he wants to see them “coming up with things that make some sense to me.”

Mr. Obama, speaking to reporters on his campaign plane today, said he will “definitely be reaching out” to Mr. Bloomberg.

“I hope that Mayor Bloomberg will look at my track record — of trying to reduce special interest influence in Washington, having common-sense energy plans that can put us on a more stable economic footing — and conclude that I’d be in the best position to put forward the kind of pragmatic kinds of common-sense solutions that he’s championing in New York,” Mr. Obama said.

Meanwhile, Mrs. Clinton told reporters after a campaign event in Ohio that she has “the highest regard for Mayor Bloomberg” and looks forward to working with him in the future.

Mr. Bloomberg, who is more aligned with Democrats and supports abortion rights, gun control, gay marriage, and stem cell research, said his endorsement will not be strictly issues-based.

The mayor, a Democrat-turned-Republican-turned-independent, said he may not agree with the candidate’s entire agenda and is more interested in the one who has a clear business plan for executing it.

Mr. Bloomberg has ties to everyone in the race.

In 2001, when Mr. Bloomberg was a politically untested businessman attempting a long-shot bid for City Hall, Mr. McCain endorsed the little-known Republican, appearing in advertisements on his behalf and joining him for campaign appearances.

“He’s independent, tough-minded, and willing to fight for what’s right,” the Arizona senator said at the time.

The pair are also socially connected, and Mr. Bloomberg hosted a fundraiser at his Manhattan home for Mr. McCain in 2003.

Meanwhile, two other centrist buddies of Mr. Bloomberg — Governor Schwarzenegger of California and Senator Lieberman — have endorsed Mr. McCain in this race.

Mr. Bloomberg also has worked closely with Mrs. Clinton, his home state senator. There may be lingering bitterness, though, left over from 2005, when he ran for re-election and she endorsed his Democratic opponent, who was not expected to win.

He has praised her in the past for being responsive whenever he needed anything. He also has struck up a relationship with her husband, President Clinton, and has worked with him on a number of climate change initiatives.

In December, Mr. Clinton praised Mr. Bloomberg and said he hoped the mayor didn’t end up running against his wife “just because I like him so much.”

Mr. Bloomberg has not known Mr. Obama for as long as Mrs. Clinton or Mr. McCain, but the pair met for a highly publicized breakfast and photo opportunity last November, and Mr. Bloomberg has praised the Illinois senator for positions such as supporting merit pay for teachers.

Mr. Obama’s embrace of bipartisan themes in his campaign is also certain to appeal to Mr. Bloomberg.

Whomever Mr. Bloomberg backs, it is likely that his endorsement would come with a heap of cash. If he had launched his own independent bid, aides said he was prepared to spend $1 billion; Forbes magazine estimates his wealth at $11.5 billion.

He indicated at the news conference that there are a number of ways he could help a candidate or put forth his own views, such as buying television advertisements. He said he does not plan to start a so-called 527 committee, a tax-exempt organization that can raise unlimited amounts of money to advocate issues to voters.