* SolarWorld plans bid for GM's Opel; GM says not for sale

* Calls mount for European aid for auto sector

* Impact spreads to BASF outlook

* Toyota to shut in U.S. output for 2 days

By Noah Barkin and Christoph Steitz

BERLIN/FRANKFURT (Reuters) - General Motors GM.N dismissed a surprise overture for its cash-strapped German unit on Wednesday as calls mounted for European governments to come to the aid of automakers hit by the global financial crisis.

German solar energy company SolarWorld (SWVG.DE: Quote, Profile, Research) shocked markets when it unveiled plans to bid for the German plants of GM unit Opel, vowing to turn the automaker into Europe's first "green" car company. [nLJ288150]

But GM, itself seeking a multibillion dollar bailout from the U.S. government, was dismissive of the takeover plan, which SolarWorld said was conditional on a complete separation of Opel from its parent company and on state guarantees from the German government.

"This is pure speculation. We are not going to comment on that. Opel is not for sale," said Karin Kirchner, a spokeswoman for GM Europe in Switzerland.