* Nike sponsors 6 of to 10 most marketable footballers
* Adidas fighting to maintain lead in soccer market
* Nike top star is Ronaldo, Adidas bets on Messi
* Even top German players defect to Nike
* Puma persuades Balotelli to wear mismatched boots
By Emma Thomasson
BERLIN, May 28 (Reuters) - U.S. sportswear group Nike is banking on its sponsorship of more of the world's best-known soccer stars than Adidas in its battle to overtake the German firm as the sport's top-selling brand at its World Cup this summer.
Nike has signed six of the 10 most marketable footballers in the world, to just three for Adidas and one for smaller German brand Puma, according to a new ranking by sports marketing research group Repucom published on Wednesday.
Portugal's Cristiano Ronaldo, sponsored by Nike, tops the Repucom ranking, with almost 84 percent of people around the world saying they know the Real Madrid striker, helping to sell over one million shirts with his name on the back in 2013.
In second place is Lionel Messi of Argentina, front man for the Adidas campaign who scores 76 percent global awareness according to Repucom - his marketability little dented by a mixed run of form for Barcelona this season.
The appeal of the extrovert Ronaldo, who took the crown as the world's best player from Messi in January, is helped by his use of Twitter, where he has 26 million followers to just two million for the more retiring Argentine.
Ronaldo probably helps sell shirts even when he isn't wearing one - he poses nude on the cover of the latest Spanish Vogue with his model girlfriend Irina Shayk - though the branding benefits are shared as Adidas sponsors Real Madrid.
"While it is primarily about performance on the pitch, a player's appeal is about a whole range of variables. With a footballer, you see everything, on the pitch and off the pitch, week in, week out," said Repucom founder Paul Smith.
"Athletes like Ronaldo have something unique that if you could bottle it and sell it, you would do nothing else."
Nike tries to do just that with a glitzy ad featuring Ronaldo - and Shayk - in which boys playing football in the local park end up scoring a penalty in a huge stadium against their heroes, including others from the Repucom top 10 such as England's Wayne Rooney and Brazil's Neymar.
Adidas has retaliated with a new ad launched last Saturday which shows Messi dreaming about his rivals such as Bastian Schweinsteiger of Germany, Luis Suarez of Uruguay and Dani Alves of Brazil, none of whom feature in the Repucom ranking.
Adidas, which has long dominated the market for soccer boots, shirts and balls, is facing a fierce challenge from Nike, the world's biggest sportswear company that has only been a serious player in soccer for the last 20 years.
While Adidas has supplied the match ball for the World Cup since 1970 and has extended its sponsorship of the competition to 2030, Nike is for the first time kitting out more teams - 10 out of 32 finalists - including hosts and favourites Brazil.
Adidas, which is supplying nine teams including reigning champions Spain, as well as Argentina and Germany, expects to make a record 2 billion euros ($2.7 billion) from football this year, still exceeding Nike's $2 billion of soccer turnover.
"Football is the DNA of our company. We want to clearly show that we are number one in football," Adidas Chief Executive Herbert Hainer told journalists last week, adding Adidas expected to sell significantly more balls than at the last World Cup in South Africa four years ago and about as many shirts.
Hainer acknowledged that Adidas faced a "head-to-head" race with Nike in the soccer shoe market, but predicted Adidas would still sell 2 million pairs of special World Cup boots.
Nike believes it has already overtaken Adidas in boots, including in its rival's home market Germany.
While Adidas will be supplying the German kit, many of the country's top players now wear Nike boots, with nine members of the team that started against Poland this month sporting Nike.
However, Hainer dismissed suggestions Adidas had not signed the right stars, saying 14 of the 27 members of the German squad would be wearing boots with Adidas' trademark three stripes.
Meanwhile, Puma, whose only player in the Repucom top 10 is former France striker Thierry Henry, is resorting to a stunt to attract attention: it has persuaded players such as Italy's maverick striker Mario Balotelli, Marco Reus of Germany and Cesc Fabregas of Spain to wear one pink and one blue "Tricks" boot.
"I have to be honest, the first time I saw the Tricks boots, I thought the Puma guy was mad. But when I realised he wasn't, I was already excited," Balotelli said.
"It is exactly the reason why I chose to be with Puma, they dare to be different and everyone knows that I do as well."
$1 = 0.7325 Euros Additional reporting by Joern Poltz in Munich; Editing by Mark Potter