It looks like big guns are coming in to defend Vladimir Gusinski, Russian media tycoon, facing fraud charges in Russia. A really sensational statement in this connection has been made by Israeli Premier Ehud Barak. He says Mr. Gusinsky should emigrate to Israel once he is released. ''I'll do everything I can so that Gusinsky can come home to Israel,'' Mr. Barak is quoted as saying. ''I have already spoken with the Spanish prime minister about this.'' It is yet unknown how the Spanish prime minister reacted to the surprise intercession of his Israeli colleague. The Spanish authorities are known to have repeatedly asserted they are not going to heed outside advice in this matter or blow up a suggested political motivation behind the case. On the other hand, if Mr. Gusinski gets a political asylum in Israel, the question of his extradition will hardly ever be raised.