UPDATE 1-NY Mayor Bloomberg says will not run for president

(Rewrites throughout with Bloomberg article)

NEW YORK, Feb 27 (Reuters) - New York City Mayor Michael Bloomberg has decided not to run for the U.S. presidency, he said in the New York Times, ending long-running speculation that he could launch a challenge as an independent candidate.

"I listened carefully to those who encouraged me to run, but I am not and will not be a candidate for president," Bloomberg said in an opinion article in Thursday's newspaper.

It was Bloomberg's most categorical statement that he will not compete in the November election against the Democratic and Republican nominees.

He told reporters earlier on Wednesday, "I'm not a candidate for president of the United States" -- a phrase he has used many times and that appeared to leave the door open for a possible late presidential run.

Bloomberg did not say why he had decided not to run and was critical of the Republican and Democratic contenders, saying they appeared afraid to "level with" voters on many important issues such as trade, the environment and immigration.

"I believe that an independent approach to these issues is essential to governing our nation and that an independent can win the presidency," he wrote. "I have watched this campaign unfold, and I am hopeful that the current campaigns can rise to the challenge by offering truly independent leadership.

Bloomberg did not endorse anyone but said he would support a candidate who "takes an independent, nonpartisan approach and embraces practical solutions that challenge party orthodoxy."

"I'll join others in helping that candidate win the White House," he said.

Bloomberg, 65, was a longtime Democrat who switched to the Republican Party to run for New York mayor in 2001. He was reelected in 2005, and then in June last year announced he had left the Republican Party to become an independent. (Reporting by Stuart Grudgings, editing by Doina Chiacu)