Dresdner's Q3 shows scale of Commerzbank task

* Dresdner posts biggest quarterly operating loss in six years * Financial market crisis hits bank's traditional business * Commerzbank shares fall 3.9 pct, biggest decliner DAX index

By Philipp Halstrick and Patricia Uhlig

FRANKFURT, Nov 10 (Reuters) - The extent of Dresdner Bank's writedowns, slowing revenue and rising costs have shed light on the restructuring task faced by new owner Commerzbank AG (CBKG.DE: Quote, Profile, Research) when it takes control of Dresdner next year.

Dresdner posted its biggest quarterly operating loss in six years on Monday, on the back of nearly 1 billion euros ($1.3 billion) in writedowns, and it is seeing its capital base eroded even as it struggles to bring costs under control. [ID:nLA603783]

The financial market crisis is also hitting hard Dresdner's traditional banking business with retail and business customers, while obscuring the bank's business outlook.

Commerzbank agreed three months ago to buy Dresdner from Allianz SE (ALVG.DE: Quote, Profile, Research) for nearly 10 billion euros, but the deal is now worth less than 8 billion euros because of the sharp decline in Commerzbank's share price.

"Commerzbank bought way too much risk for way too high a price," Landsbanki Kepler analyst Dirk Becker said, adding that the risks were too big to assess properly.

Commerzbank shares fell 3.9 percent to 8.11 euros by 1552 GMT, making it the biggest decliner on Germany's blue-chip DAX .GDAXI index, which was up 2 percent. It also lagged a 1.3 percent decline in the DJ Stoxx European banking index .