VIENNA (Reuters) - Austria s co-governing Social Democrats (SPO) and conservative (OVP), who are leading in polls ahead of the Oct. 15 election, said on Friday they would sue each other in an escalating political smear scandal. A public outcry over derogatory Facebook pages targeting OVP leader Sebastian Kurz, run by campaign consultants hired by the SPO, has already led to the departure of its campaign manager and loss of popularity in a recent poll.  The limit has been reached. We re suing,  OVP general secretary Elisabeth Koestinger told a news conference. She said her party was preparing a libel suit against an employee of SPO campaign consultant Tal Silberstein, whom the SPO fired in August, to force him to retract comments that the OVP had offered him 100,000 euros ($116,980) to switch sides.  We are also preparing to sue the SPO in relation to incitement,  she said, adding the lawsuit could be broadened. SPO chairman Christoph Matznetter said the SPO was preparing a lawsuit against Kurz s spokesman seeking to clarify whether he did or did not offer money to Silberstein s employee. He said such an act could amount to bribery and  industrial espionage . SPO Chancellor Christian Kern, who has governed in a tension-ridden  grand coalition  with the OVP, has said he knew nothing of the  dirty campaigning  pages and has asked Facebook to unmask the people running them. At the behest of the SPO, Vienna prosecutors are investigating unnamed persons for defamation as the pages also included derogatory content aimed at Kern.  The OVP is leading pre-election polls at around 34 percent, while the SPO has slipped to third place at 22 percent below the far-right, anti-immigrant Freedom Party at 27 percent. 