MADRID, Dec 19 (Reuters) - Forty-seven members of front groups for Basque separatist guerrillas ETA were sentenced to a total of more than 500 years in prison by Spain's high court on Wednesday after one of the longest trials of its type here.

Those convicted belonged to groups such as Ekin, Kas and Xaki, which performed tasks including conducting international relations for ETA.

Of those sentenced to up to 20 years in prison, 31 were found guilty of belonging to a terrorist organisation, court officials said.

The sentences were read out after a trial which began in late 2005 and almost a year after Spain's Socialist government called off peace talks with ETA after the rebels killed two people with a car bomb at Madrid airport.

Another five accused were acquitted.

ETA has killed more than 800 people in over four decades of violent struggle for independence in Basque territories in northern Spain and southern France.

The Basque issue is looming as a major issue in Spain's general elections due next March, with the conservative opposition criticising the government for failing to rule out all future negotiations with the separatists.

The reading of Wednesday's sentences at a high security courtroom in Madrid parklands was delayed after disturbances broke out when the accused tried to sing Basque nationalist songs. (Reporting by Teresa Larraz, editing by Ibon Villelabeitia)

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