The suspected top political leader of the Basque separatist group ETA has been arrested in southwestern France in a joint operation by French and Spanish police, Spanish anti-terrorism sources said.  Javier Lopez Pena, alias "Thierry", who is considered by Spanish authorities be the top political leader of ETA, was among the four people detained in the raid in the southwestern city of Bordeaux.   The organisation is blamed for the deaths of over 820 people in its 40-year campaign for an independent Basque nation.  The other three arrested in the operation against ETA's political leadership were named as Ainhoa Zaeta Mendiondo, Igor Suberbiola and Jon Salaberria.