DETROIT (Dow Jones)-General Motors Corp. (GM) won backing Thursday from key creditors for a bankruptcy plan that would give the U.S. government a 72.5% stake in a "New GM".

The new proposal outlined in a regulatory filing set a Saturday deadline for bondholders to accept an offer sweetened with warrants and additional federal backing.

With GM expected to file for court protection Monday, progress in the U.S. came as parallel efforts to restructure its European operations suffered a setback.

The German government criticized the negotiating stance of the company and the U.S. government, and delayed a decision on providing bridge loans to its Opel/Vauxhall units until Friday.

Under the proposal, the U.S. Treasury would loan GM at least $50 billion to fund the company through bankruptcy proceedings and finance the entity that emerges from Chapter 11. The government would be repaid through equity in the new GM

The United Auto Workers would receive 17.5% to fund a retiree health care trust, with 10% going to creditors - in line with the offer they rejected Tuesday - though warrants could substantially increase that amount.

Bondholders, who soundly rejected an offer to swap $27.2 billion in debt for 10% equity in the new company, would have rights to buy an additional 15% of GM's stock at a lower price.

"The Ad Hoc Committee of GM bondholders supports the revised offer from GM and believes that when contrasted with the alternative - uncertain and costly bankruptcy court litigation - that it represents the best alternative for bondholders in the current difficult and dire situation," it said in a statement.

Bondholders have until 5 p.m. Saturday to decide whether to accept the offer. The ad hoc committee representing institutional investors had previously said it would oppose both the debt swap and GM's bankruptcy plans to sell assets.

The group's support is critical in winning approval from the larger number of GM bondholders, but far from guarantees success.

A separate group representing small individual bondholders who hold about 20% of the company's bond debt said Thursday the new proposal doesn't look much better.

"From what many of our bondholders have heard, it's still a bad offer because it only gives bondholders 10% of the company," said Sarah Jackson, a spokeswoman for the Main Street Bondholders.

The Canadian federal government and the province of Ontario also are both slated to receive some equity and preferred stock in return for debt financing.

The filing didn't mention existing ordinary shareholders, who are expected to be wiped out having been originally due to receive 1% in a 'New GM", though its shares recently rose 9.57% to $1.26.

GM's U.S. workers are voting Thursday on contract amendments that are also required, alongside creditor backing and a broader viability plan, to meet the June 1 deadline set for securing extra U.S. government support.

-By Sharon Terlep; 248-204-5532; sharon.terlep@dowjones.com.

(Joshua Mitchell contributed to this report)