(Refiles to clarify quote in para 20, UEFA not FIFA)
* Platini will not stand against Blatter
* Frenchman says he still believes change needed at FIFA
* Blatter set to seek fifth term
By Mike Collett
MONACO, Aug 28 (Reuters) - UEFA president Michel Platini ruled himself out of the running for the most powerful job in football on Thursday, saying he "could not convince himself" that opposing incumbent Sepp Blatter for the FIFA presidency was the right thing to do.
Instead, the former France international told a packed news conference in Monte Carlo that he would offer himself instead for re-election as UEFA president, a role he has held since 2007.
Platini, 59, had already told the chairman and general secretaries of UEFA's 54 member nations that he would not be standing against the 78-year-old Swiss, who is expected to seek a fifth term at the helm of the world governing body when the election is held next June.
The Frenchman said he had deliberated for months before deciding against standing, but still believed change was needed at FIFA and it was time Blatter went.
The Swiss has held the FIFA presidency since 1998 and has indicated he will stand again, despite criticism that the game and FIFA have been tarnished by allegations of corruption during his reign.
"I have thought long and hard about this over many months but I have never managed to convince myself that I had to go to FIFA. It's really that simple," said Platini of his decision. "My will is to run for a new term of office for the presidency of UEFA.
"I told the chairmen this morning this a choice from my heart, based on football and based on my passion," added Platini.
"We have big projects ahead at UEFA and I have the motivation to carry them out before one day moving on to something else, but now is not the time, or my time for FIFA, not yet."
Platini, who is a vice-president of FIFA and sits on the FIFA executive committee, said he had made his decision "without the slightest shadow of regret".
Just before the World Cup started last June, Platini called for a "breath of fresh air" at FIFA and said he no longer supported Blatter's position as president.
He returned to that theme on Thursday saying: "Some of you expected me to attack FIFA today, but that is not my goal here.
"But we do want a FIFA that works better, with more transparency and solidarity and is more respected by those that love football.
"I have looked Sepp Blatter in the eye. I have told him I no longer support him and there should be change," he added.
Asked if he decided not to run against Blatter because he knew he could not beat him in an election race, Platini disagreed.
"I don't think you can say that. When I ran for the UEFA presidency in 2007 Lennart Johansson was the president and that was no mean feat to beat him, so I can't be accused of being afraid," he said.
"I think Blatter will run again, but although I helped him in 1998, 2002, 2007 and 2011, he no longer has my support and I hope there will be a challenger, but I don't know.
"While respecting the work of the president, we need a strong FIFA executive committee to work as a counter-balance. The president should not be omnipotent."
The only person so far to declare his intention to run is former FIFA deputy secretary general Jerome Champagne, 56, who announced his candidature in January and has recognised he is the underdog.
Asked what he thought of Champagne's chances, Platini replied: "I don't think there is much interest there."
In response, Champagne told Reuters by telephone: "If elected I very much look forward to working with Michel Platini to stop 25 years of tension between the world governing body and UEFA."
Blatter was first elected president in 1998 and possible candidates have until January to declare their intentions.
The Swiss has been a controversial figure, and has had to face allegations focused in particular on the awarding of the 2018 and 2022 World Cups, soccer's showpiece events, to Russia and Qatar.
David Triesman, former head of English soccer's governing body, told the upper house of Britain's parliament in June that FIFA behaved "like a mafia family" and had "a decades-long tradition of bribes, bungs and corruption."
Blatter has acknowledged he did not vote for Qatar, while Platini has said he did. (Reporting by Mike Collett, editing by Alan Baldwin)