Telekom Austria cuts outlook on Q3 net loss

* Q3 net loss 136 mln eur vs poll avg net profit 132 mln eur

* 352 mln eur goodwill writedown on Belarus, Serbia

* Cuts EBITDA, revenue outlook, keeps dividend, cashflow

* Blames fx, weak E.Europe economies, roaming price cuts

(Adds details, background)

VIENNA, Nov 12 (Reuters) - Telekom Austria (TELA.VI) swung to a surprise loss in the third quarter due to goodwill writedowns for eastern European assets and cut its full-year core earnings outlook after missing estimates for the quarter.

The group reported a net loss of 136.3 million euros ($204.2 million) after writing 352 million euros off the value of its mobile operators in Belarus and Serbia, once among its growth hopes but now a drag on earnings as crisis hits the region.

Analysts polled by Reuters had on average expected net profit of 132 million euros and EBITDA of 502 million euros.