* Catalan separatist parties win a majority in regional parliament
* Main separatist group CiU loses ground, partial results show
* Artur Mas may not have mandate to hold independence referendum
By Fiona Ortiz and Braden Phillips
BARCELONA, Spain, Nov 25 (Reuters) - Four separatist parties in Spain’s Catalonia looked set to win a majority in regional elections on Sunday, partial results showed, but the main one was on course to lose some seats, possibly undermining its bid to call an independence referendum.
With half of votes counted, the ruling Convergence and Union alliance, or CiU, was winning 48 seats in the 135-seat local parliament, well down from its current 62 seats.
The separatist Republican Left, or ERC, was winning 20 seats, with two other smaller separatist parties taking a total of 16 seats, giving the four parties 60 percent between them.
Regional President Artur Mas, of CiU, had campaigned on a pledge to hold a referendum on independence, in response to a resurgent separatist movement among Catalans who are frustrated with Spain in a deep economic crisis.
Opinion polls had forecast that CiU would retain 62 or more seats in the local Parliament and that all four separatist parties would have more than two-thirds of the seats. Neither of those projections was met as the results began to come in.
Without the psychological backing of a two-thirds majority, analysts have said, it may be hard for Mas to defy the constitution and the central government in Madrid and try to hold a referendum.
Turnout was very high in the election, 68 percent, 10 percentage point higher than in the previous vote two years ago.
With more people than Denmark and an economy almost as big as Portugal‘s, Catalonia has its own language. Like Basques, Catalans see themselves as distinct from the rest of Spain.
Growing Catalan separatism is a huge challenge for Prime Minister Mariano Rajoy, who is trying to bring down painfully high borrowing costs by persuading investors of Spain’s fiscal and political stability.
Mas converted to separatism after huge street demonstrations in September.
Up until recently Mas was a moderate nationalist who had pushed Spain to give Catalonia more self-governing powers. He has followed the popular mood in converting to a more radical separatism, but it is not clear he can hold a referendum legally.
Many Catalans are angry that Rajoy has refused to negotiate a new tax deal with their largely self-governing region. Annually, an estimated 16 billion euros ($21 billion) in taxes paid in Catalonia, about 8 percent of its economic output, is not returned to the region.
Home to car factories and banks that generate one fifth of Spain’s economic wealth, and birthplace of surrealist painter Salvador Dali and architect Antoni Gaudi, the region also has one of the world’s most successful football clubs, FC Barcelona.