Berlin - The battle for General Motors Corp's European offshoot Opel entered a decisive phase Monday with the US carmaker expected to begin considering offers for the group.

The board of the Canadian-Austrian car parts supplier Magna International, which has linked up with the state-controlled Russian savings bank Sberbank and Russian carmaker Gaz, gave the green light to the group's bid for Opel, which also includes Britain's Vauxhall brand.

A key question is the future role to be played by GM, which is hiving off a majority stake in its European operations after slumping sales forced it to embark on a major restructuring of its global business.

The Magna consortium is one of three possible bidders for Opel. The others are Brussels-based private equity group RHJ International and China's Beijing Automotive Industry Holding Company (BAIC).

The Italian car group Fiat has also expressed an interest, but Magna and RHJ appear to have emerged as the frontrunners in the battle for the GM unit, which has been placed in the hands of a trustee controlled by both GM and the German government.

"Our negotiations with GM are well advanced," said RHJ spokesman Arnaud Denis.

GM, which only emerged this month from bankruptcy, is expected to present its preliminary findings on the bids to the German and other European governments on Wednesday

While the Magna group plans to invest 500 million euros (705 million dollars) and has called for 4.5 billion euros in state guarantees, BAIC is bidding 660 million euros and has requested only 2.64 billion euros in government support.

Magna, which has already won strong political backing in Germany, envisages GM emerging with a 35 per cent stake in Opel, Magna and Sberbank together holding 55 per cent, and the workforce 10 per cent. Magna plans to boost Opel's presence in the emerging Russian car market.

Speaking in Munich last week, German Chancellor Angela Merkel said the Magna-led offer was an "excellent starting point" for securing Opel's future, although she added "many issues still needed to be cleared up."

RHJ wants to take out a 50.1-per-cent stake in Opel worth about 300 million euros. Under the RHJ plan, GM would have a 39.9-holding in what the Brussels-based investment group calls New Opel, with the European carmaker's employees holding 10 per cent.

In the documents setting out its Opel bid, RHJ also envisages the possibility that GM could eventually buy it out as part of an exit strategy should its offer succeed.

RHJ says that it did not plan to exit Opel until the government- backed loans have been repaid in full by 2014.

The RHJ document goes on to say that in the case of an exit "all steps have been taken to prepare for an independent New Opel to be sold." This includes to a third party, GM or through a stock market listing.

But in an interview with Sunday's Frankfurter Allgemeine Sonntagszeitung, Germany's economics minister rebuffed suggestions that GM could include an option to regain majority control of Opel as part of a deal in the bidding war.

"This is incompatible with our views and cannot happen," said Karl-Theodor zu Guttenberg.

While a final decision could take until the end of the month, GM is also expected to make a series of presentations to its board and the US Treasury. The US government has 60.1-per-cent stake in GM.

With the German government having agreed to help keep Opel afloat with 1.5 billion euros in short-term loans, Berlin's view of the potential bidders could be crucial in deciding the outcome.

The Opel bidding war comes at a particular sensitive time for Berlin as it prepares for national elections in September.

The Magna-led bid is likely to result in about 11,000 cuts in Opel's 55,000 strong European workforce.

A successful bid from RHJ could result in the loss of 3,900 jobs in Germany as part of a cutback of 9,900 Opel jobs across Europe.(dpa)