* Blatter failed to win two-thirds majority
* Wins amid criminal probes of corruption in FIFA
* Blatter promises to revive world soccer body's reputation
* Opponents say crisis within group not resolved
* Graphics: link.reuters.com/fac84w
By Mike Collett and Brian Homewood
ZURICH, May 29 (Reuters) - Sepp Blatter was re-elected president of FIFA for a fifth term on Friday after his only challenger conceded defeat in an election overshadowed by allegations of rampant corruption in world soccer.
Blatter won despite demands that he quit in the face of a major bribery scandal being investigated by U.S., Swiss and other law enforcement agencies that plunged soccer's governing body into the worst crisis in its 111-year history.
Yet his mandate, which was far from convincing, raises fresh questions over his leadership with the possibility of civil war in international football, unhappy sponsors demanding reform and prosecutors looking to widen their investigations.
Neither Blatter nor Jordanian opponent Prince Ali bin Al Hussein received the necessary two thirds of votes in the first round, with Blatter securing 133 votes against 73 for Prince Ali. However, Prince Ali swiftly conceded.
"I congratulate you if you voted for Prince Ali, he was a good candidate, but I am the president now, the president of everybody," the 79-year-old Blatter said in his victory speech, knowing he faces a barrage of criticism and countless problems.
UEFA, the powerful European confederation, has been staunchly opposed to another term for the Swiss official and UEFA president Michel Platini has even raised the possibility, albeit unlikely, of Europe boycotting the World Cup.
There has also been talk of UEFA breaking away from FIFA, which is also unlikely, but nothing can be ruled out.
Blatter's future could yet depend on the reaction of FIFA's major sponsors and stakeholders who have been deeply dismayed by the dawn arrests in Zurich on Wednesday of several FIFA officials and U.S. prosecutors announcing indictments of officials and companies.
One top sponsor, Anheuser-Busch, the maker of Budweiser, said after Blatter's win that: "We expect the next FIFA presidency to resolve internal issues, install positive change and adhere to strong ethical standards and transparency."
FIFA, ruled over by Blatter since 1998 and long been subject to suspicions of corruption and internal probes, has had a traumatic week with law enforcement stepping in with allegations of financial wrongdoing stretching back 24 years.
Blatter has batted away the controversy, relying on his network of friends to hold onto power at FIFA, (Fédération Internationale de Football Association).
Prince Ali, in his pitch for votes, had pledged an open, more democratic FIFA, saying: "We have heard in recent days, voices which described our FIFA as an avaricious body which feeds on the game that the world loves.
"There are no easy answers. And no blame that can be cast that will wash away the stain that marks us all," he said.
Blatter told FIFA TV that he knows how to create a better image for the organization and promises to unveil surprising plans on the first working day of his new term.
"It was a very difficult Congress due to the circumstances of these events," Blatter said. "I would say also kind of tragic events, Wednesday and Thursday in Zurich and all with the media in the world, what they said about FIFA."
While Asian, African and Latin American states had been expected to rally around Blatter, Europe, which accounts for all but three of the countries that have ever made it to the final of the World Cup, had been keen for him to step aside.
European soccer chiefs said after the vote that FIFA had to embrace reform. "Change in my opinion is crucial if this organisation is to regain its credibility," said Platini.
In federal court in Brooklyn, New York on Friday, one of the people accused, the American head of a Brazilian sports marketing company, pleaded not guilty to bribery-related charges.
Aaron Davidson, 44, head of Traffic Group's U.S. unit in Miami, is accused by prosecutors of securing contracts worth more than $35 million for the unit he ran and of arranging bribes for Jeffrey Webb, a FIFA vice president. A judge granted Davidson bail but ordered him to be put under house arrest in Miami and to wear an electronic monitoring device.
The United States, which last hosted the World Cup in 1994, is interested in hosting the 2026 edition but has not yet formally applied. U.S. Soccer President Sunil Gulati said in a statement after Blatter's re-election that it would "continue to push for meaningful change within FIFA."
Swiss prosecutors are investigating the award of the World Cup finals to Russia in 2018 and Qatar in 2022. Russia and Qatar deny wrongdoing in their bids to host the tournament.
Britain's Serious Fraud Office said it was examining possible corruption at FIFA and authorities in Argentina and Brazil have also opened investigations.
A judge in Argentina has ordered the arrest of three businessmen accused of using bribery to obtain soccer media rights, and the Brazilian Senate moved to open a formal inquiry into soccer bribery allegations.
Marco Polo Del Nero, the president of the Brazilian Football Confederation, dramatically flew back to Brazil from the FIFA Congress before the vote. Former Brazilian soccer chief Jose Maria Marin was arrested this week in the case.
Del Nero told a press conference on Friday he did not plan to resign and "had nothing to do" with corruption.
FIFA takes in billions of dollars in revenue from television marketing rights and sponsorships, making it one of the wealthiest and most powerful sports bodies in the world.
When asked after the vote if he could guarantee the next World Cup would still be staged in Russia, FIFA's secretary general Jerome Valcke told reporters: "Yes, yes. I mean now today, if you ask me the question at twenty to eight, yes the World Cup will be played in Russia and Qatar.
Russian President Vladimir Putin has accused the United States of meddling in an effort to force Blatter out.
Russia's Sports Minister Vitaly Mutko told state broadcaster Rossiya24 they were happy with the outcome of Friday's vote and added that the timing of the arrests had been chosen to complicate Blatter's re-election.
"In general, of course we are pleased with the result. Russia was backing Blatter. We also believe... much needs to be done to change football," Mutko said.
Qatar on Friday issued a further defence of its bid and said it would carry on with plans to stage the 2022 event.
The decision to host the world's biggest soccer tournament in a small desert state where daytime summer temperatures rarely fall below 40 degrees Celsius startled many in global sport, and went against the advice of FIFA's own technical committee.
Many of Blatter's opponents have spoken of steps they can take against him. English Football Association chairman Greg Dyke, who has suggested that England might back a possible boycott of the 2018 World Cup, said FIFA's crisis was not over.
"This is the beginning, not the end. I think there is a lot more of this to play out," Dyke told Sky News.
Blatter had repeatedly promised not to stand for re-election again, but as his fourth mandate drew to a close he changed his tune and said he needed yet another term to complete his work.
The newly-constituted FIFA executive committee meets for the first time on Saturday to discuss slots for the 2018 and 2022 World Cup finals.
Platini has warned Blatter he will not tolerate losing any of Europe's 13 places. If Blatter attempts to do that and Europe is outflanked in an executive committee vote, international football could be plunged into civil war.
Most of Africa, Asia and parts of Central America and the Caribbean are happy that FIFA under Blatter has guaranteed them annual grants and bonus payments in World Cup years.
Addressing the Congress on Friday, Blatter promised to boost the profile of Pacific island soccer federations grouped in Oceania, and said more had to be done to promote women in the game. The FIFA Women's World Cup starts in Canada on June 6.
"Let's go FIFA, Let's go FIFA," Blatter said to a standing ovation. (Writing by Giles Elgood and Crispian Balmer; Editing by Ian Chadband and Grant McCool)