After two years of playing coy about his presidential ambitions, Mayor Bloomberg said today he will not run for president as an independent, declaring in a newspaper editorial that he might lend his support to the candidate who “takes an independent, nonpartisan approach.”

The 66-year-old billionaire businessman, who aides had said was prepared to spend $1 billion on his own independent campaign, wrote in a New York Times editorial that he will be working to “steer the national conversation away from partisanship and toward unity; away from ideology and toward common sense; away from sound bites and toward substance.”

Mr. Bloomberg, who has almost two years left in his second term at City Hall, had publicly denied any interest in running for president since one of his political advisers first planted the seed more than two years ago.

But his denials grew weaker in recent months as aides and supporters quietly began laying the groundwork for a third-party campaign.

Among his biggest obstacles was getting on the ballot, a process that varies wildly from state to state and would have required him to obtain hundreds of thousands of signatures according to a timetable whose first key date is next March 5.