General Motors Corp faces a number of major deadlines and events on Tuesday that will go a long way toward determining how and when the company files for an expected bankruptcy later this week.

The most anticipated event is how much of GM's $27 billion in bond debt is revealed to have been tendered in exchange for shares. GM has set a target of slashing 90 percent of its bond debt, a goal analysts see as unlikely.

Also on Tuesday, officials at the United Auto Workers' union will gather to hear how many U.S. factory jobs GM will cut as part of its restructuring.

Union officials representing 54,000 GM workers are scheduled to meet to prepare for a quick ratification vote on a cost-cutting labor deal negotiated last week. The union aims to complete those votes by Thursday.

Approval of the contract, which would change payment terms on $20 billion owed to a UAW trust fund, represents one of the hurdles for GM to clear before a June 1 deadline set by the Obama administration.

But bondholders have balked at proposals that they forgive debt in exchange for a 10 percent stake in a restructured company.

Under GM's current plan, a UAW trust fund for healthcare would receive a GM stake of about 39 percent. The U.S. Treasury would hold a 50 percent stake. Current shareholders would be left with just 1 percent of a restructured company.

The standoff between GM and its bondholders sets the stage for a bankruptcy filing, analysts have said.

A person familiar with Obama administration thinking on the matter said the administration was continuing to engage with bondholders to reach agreement.

The person, who was not authorized to speak publicly on the situation, reiterated that there were no plans to steer GM into a bankruptcy filing before June 1.

Shares of GM, which the automaker has warned could be worthless in a bankruptcy, were down 12 cents or 8.4 percent at $1.31 on the New York Stock Exchange on Tuesday morning.

The bondholder deadline is scheduled for midnight and coincides with a turning point for smaller rival Chrysler, which has been operating in bankruptcy since April 30.

Bankruptcy Judge Arthur Gonzalez could rule as early as Wednesday on whether Chrysler will be allowed to sell its most valuable assets to a new company that would be under the operational control of Italy's Fiat SpA.

The U.S. government has provided a combined $36.6 billion to GM, Chrysler and their financing units since December.

In an interview broadcast over the weekend, Obama said he hoped GM and Chrysler would emerge from restructuring leaner, meaner, more competitive.

Ultimately, I think that GM is going to be a strong company, he said.

THE OPEL SAGA

While much attention will be on Washington and Detroit, talks continue in Europe over the possible sale of GM's Opel unit.

On Tuesday, Germany pressed the three bidders for Opel to improve their offers for the carmaker, saying they needed to assume greater risks and make credible commitments to preserve jobs and sites.

Economy Minister Karl-Theodor zu Guttenberg told reporters after meeting Fiat Chief Executive Sergio Marchionne in Berlin that the Italian carmaker's offer looked serious but that rival bidders Magna and RHJ International remained in contention.

There's no favorite, he said. Everyone knows that improvements are still necessary.

Fiat made an aggressive last-ditch push to convince the German government to back its bid for Opel ahead of a top-level meeting in Berlin on Wednesday where a preliminary decision on preferred bidders is expected.

Marchionne met with Chancellor Angela Merkel and Guttenberg on Tuesday morning to try to address German concerns about his ambitious plan to fold Opel into a transatlantic car empire that would also include U.S. carmaker Chrysler.

The German government hoped to be able to settle on one or more preferred bidders late Tuesday or Wednesday, a step which could lead to further negotiations.

Pressure to choose a preferred bidder is building ahead of the June 1 restructuring deadline for GM set by the U.S. government.

Across the border in Canada, GM workers at plants in Ontario on Monday ratified concessions negotiated last week with a vote of 86 percent in favor.

(Reporting by John Crawley and Kevin Krolicki; additional reporting by Andreas Moeser, Noah Barkin, David Lawder and Nick Carey; editing by Patrick Fitzgibbons and Matthew Lewis.)

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