The German government Friday stepped up pressure in its efforts to help rescue Adam Opel AG, saying an orderly insolvency would be an option for General Motors Corp.'s (GM) German unit if none of the bids for the German carmaker are solid or if a considered trusteeship fails to get support.

"The trusteeship model with a guarantee... will only materialize if the yet to be submitted concepts by the bidders are solid," German Economics Minister Karl-Theodor zu Guttenberg said in a statement.

"Should the later not be the case or should the trusteeship model not be accepted by the participants, then an orderly insolvency could be a starting point for a successful new beginning of the company and its employees."

The comments come after the government announced Thursday a state-supported trusteeship to keep the German carmaker operating, should its parent company GM enter bankruptcy before Opel can be sold.

Such a trusteeship step, which includes bridge financing for the company during the coming months, will only be considered if at least one of two known bidders for Opel submit detailed feasible bids by May 20, which have to include plans for the German production sites and jobs.

The U.S. Treasury and GM would have to support such a trusteeship which would buy time for negotiations with an investor in the company's European operations. The advantage for the German government would be that it will have a direct say in the search for an investor. At the same time, this would help the U.S. to maintain its influence in its European operation instead of losing it to the insolvency procedure.

The German government has ruled out taking a stake in Opel.

Italian automaker Fiat SpA (F.MI) and a consortium including Canadian auto parts maker Magna International Inc. (MGA) remain the two prominent interested parties.

A person familiar with the situation has reportedly said that RHJ International (RHJI.BT), a European buyout firm with holdings in the auto-parts sector, is interested in GM's European operations.

GM must institute a variety of cost reductions, including culling its dealerships and narrowing debt by a June 1 U.S. government deadline or face bankruptcy.

A trustee solution might be needed because GM might file for Chapter 11 bankruptcy late May.

A trusteeship and bridge financing would keep Opel operating to allow takeover negotiations to continue without tapping taxpayer money.

Opel might get a credit line provided by Kreditanstalt fuer Wiederaufbau, a state-owned bank for infrastructure financing, and state-owned banks in states that have Opel plants.

Carl-Peter Forster, head of GM's European operations, which also includes its Vauxhall unit in the U.K., has said Opel would need more than EUR1 billion in credit.

State-operated trustee arrangements played a major role in restructuring East German industry after the country's 1990 reunification.

-By Andrea Thomas, Dow Jones Newswires; +49-30-288-8410; andrea.thomas@dowjones.com