The German government is examining competing plans to invest in carmaker Opel and aims to decide by the end of the month whether to provide the firm with financing guarantees, a leading Social Democrat (SPD) said.

Italian carmaker Fiat is seeking a three-way merger with Chrysler and the European operations of General Motors , which include Opel.

Its main competitor appears to be Austrian-Canadian car parts maker Magna , which is seeking Russian backing for an investment in Opel.

The government is comparing the two concepts in order to make a decision on the required billions of euros in guarantees by the end of May, Peter Struck, parliamentary leader for the SPD, told the BZ newspaper.

The SPD is junior partner to Chancellor Angela Merkel's conservatives in Berlin's uneasy grand coalition.

Sovereign wealth funds based in Abu Dhabi have also been rumored to have an interest in Opel.

But United Arab Emirates Economy Minister Sultan bin Saeed al-Mansouri denied after talks with visiting German Economy Minister Karl-Theodor zu Guttenberg that there were any plans to invest in the Ruesselsheim-based carmaker.

Guttenberg told reporters on the trip that Germany was preparing for the possibility that Opel's U.S. parent could be forced into bankruptcy early next month.

He said that in the event of a GM bankruptcy, Opel assets could be handed over to a trustee who would ensure the interests of creditors.

Guttenberg described this as a precondition for Germany providing financing guarantees.

I want to protect German taxpayers from investing in an uncertain future for Opel and ending up caught in a game between GM and possible investors, Guttenberg said.

Separately, Russian Prime Minister Vladimir Putin was quoted as saying in an interview with Japanese media that Magna had asked Russian financial institutions and debt-laden carmaker GAZ to bid for a stake in Opel.

These are commercial questions. Everything needs to be carefully calculated, Putin said. The Russian government is attentively following what is going on.

(Reporting by Gernot Heller; Writing by Noah Barkin)