FRANKFURT – The proposed sale of Adam Opel GmbH by General Motors Co. to a consortium led by Canadian mega-supplier Magna International Inc. is a “welcome” development, the German auto maker’s top executive says in an appeal for calm.

Supervisory Board Chairman Carl-Peter Forster’s message, delivered to journalists here at the Frankfurt auto show, echoes a plea made by top Magna executives. Opel and Magna have dodged accusations the deal bodes ill for Germany.

“Allow us to do our work,” Forster asks of “critics,” who have raised red flags about Russia-based OAO GAZ Group’s role in the consortium and the associated fear that Opel jobs will be shipped out of Germany.

Meanwhile, Magna Co-CEO Siegfried Wolf hints the supplier’s contract-assembly plant in Graz, Austria, could build Opel vehicles. And GM’s design chief says the U.S. auto maker will maintain a measure of influence, at least near term, over future Opel products.

If finalized, the proposed deal would give Magna and its Russian partners, state-controlled OAO Sberbank and GAZ, an equal share of a 55% stake in Opel. GM would retain 35% while Opel workers would hold the remaining 10%.

GAZ is expected to benefit, through negotiated agreements, from Opel-developed technology as both auto makers compete for buyers in the potentially explosive Russian market.

Forster is mum on detailed scenarios but describes as “mutually complementary” any comparison of Opel and Magna, arguably the global industry’s most diversified supplier.

Further upstream, he confirms GM and Opel will continue to share technology while also combining forces to boost their purchasing power.

Listening to Forster here is Ed Welburn, GM’s global design chief.

“As far as I know, the relationship (between GM and Opel) will still be there,” Welburn tells Ward’s. “I don’t know in detail how it will function. What I do know, I feel good about. I’ll know more in the next few days.”

Against this tense backdrop, Forster unveils two new Opel vehicles: the 10th generation Astra C-car, which starts at E15,900 ($23,208), and the Opel Ampera extended-range electric vehicle.

Sharing its powertrain with the Chevrolet Volt, the Ampera will launch in continental Europe in 2011 and the following year in the U.K. under the Vauxhall brand.