General Motors Corp finished a key piece of business on Saturday before a bankruptcy filing planned for Monday as the deadline expired for bondholders to accept an exchange offer brokered by the Obama administration.

The development came as GM's board met for a second consecutive day to review developments and finalize plans for what has become the most widely telegraphed and carefully orchestrated bankruptcy in the history of American business.

GM would not comment on how many investors had expressed support for its bondholder swap that would give them up to 25 percent ownership of a reorganized company in exchange for $27 billion in bond debt.

GM bondholders had until 5 p.m. EDT to register their support for the deal. A group representing about a dozen major GM bondholders also had no comment.

A bankruptcy filing by GM would rank as the third-largest bankruptcy in U.S. history and the largest and most complex manufacturing bankruptcy ever.

GM has been losing market share since the early 1980s when it commanded 45 percent of the U.S. market. It has been hurt by its reliance on a truck-dominated vehicle line-up and by a deep plunge in demand as credit tightened in 2008.

Since last week, GM has been racing to complete a series of last-minute deals intended to help speed its way through a fast-track bankruptcy that would see it emerge under the majority ownership of the U.S. government.

Those deals have included a new contract for the United Auto Workers union and an agreement to spare GM's Opel brand from collapse in a deal brokered by the German government.

Bondholders have been one of the last pieces to fall into GM's complicated bankruptcy puzzle under the direction of the autos task force appointed by the White House and headed by former investment banker Steve Rattner.

GM is readying a filing for Chapter 11 protection on Monday and President Barack Obama is expected to discuss the government's unprecedented role in the remaking of an American industrial icon.

The U.S. government plans to invest a total of $60 billion in GM. A further $12.5 billion of government funding has gone to its affiliated finance company GMAC.

My preference would have been to stay out of it completely, Obama said in an interview with NBC News recorded on Friday at the White House and aired on Saturday. But the alternative was to see a liquidation, bankruptcy in which an enormous institution with huge importance to our economy simply gets broken up into pieces.

U.S. officials said on Saturday they welcomed a deal clinched by Germany with Canadian auto parts group Magna, GM and the U.S. government to save German carmaker Opel from GM's imminent bankruptcy.

This deal is a positive step for the auto industry. The auto task force will continue its close engagement with the German government on the issue, a senior administration official said.

MOVING ON GOVERNMENT TIME

In late March, the Obama administration put the automaker on 60-day notice to restructure and clinch concessionary deals with its union and bondholders.

The U.S. government has already pumped $19.4 billion in emergency funds into the Detroit-based automaker since the start of the year.

The White House has said the speed of the bankruptcy proceedings for Chrysler LLC since April 30 demonstrate the possibility of an orderly restructuring of a major U.S. carmaker and could be a model for GM.

GM Chief Executive Fritz Henderson is scheduled to host a news conference on Monday in New York -- the location of the Chrysler bankruptcy proceeding and the likely site of the court that will oversee GM's reorganization.

GM's bankruptcy is also likely to add to the strain on the auto industry -- including rival Ford Motor Co and suppliers, many of which are already struggling to survive as GM's purchasing budget runs to about $94 billion annually.

The real question is what's going to happen to the supply base now, said Dennis Virag, president of Michigan-based Automotive Consulting Group.

While a bankruptcy by a company that once led the global auto industry will be an economic milestone, it will no longer be a shock.

GM's former CEO, Rick Wagoner, was fired by the Obama administration at the end of March for having closed the door to bankruptcy. By contrast, Henderson, his successor, has said repeatedly that bankruptcy was probable.

In order to shield workers and suppliers from any bankruptcy-related disruption in payments, GM last week made early parts and wage payments.

Shares of GM fell below $1 on Friday, a level last seen during the Great Depression. The stock closed at 75 cents on what is expected to be its last trading day before bankruptcy.

GM has lost $88 billion since 2005 as it struggled to slash production capacity and jobs. It has burned through $68 million a day over the past year and $111 million every day in the most recent quarter as its sales slump deepened.

Since 2000, GM has slashed over 100,000 jobs in the United States. An additional 21,000 GM factory jobs are scheduled to be cut under the deal just approved by the UAW.

(Reporting by Poornima Gupta and Kevin Krolicki; additional reporting by Matt Spetalnick and Walden Siew; Editing by Patrick Fitzgibbons and Peter Cooney)

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