DENVER -- United Airlines stock lost two-thirds of its value Thursday amid rampant speculation that the world's second-largest carrier can do nothing except file for bankruptcy.

The New York Stock Exchange had stopped trading in United parent UAL Corp.'s shares for most of the morning because of "news that's pending that could materially affect the trading of the stock," NYSE spokesman Ray Pellecchia said.

United's parent, UAL Corp., opened at $3.12 on the New York Stock Exchange and closed at $1, the lowest level in more than 40 years.

Trading was suspended for most of the morning because of what the NYSE said was "news that's pending that could materially affect the trading of the stock." But trading resumed later in the day with no announcement from United on its next move.

Analysts said the rejection of United's request for $1.8 billion in federal loan guarantees all but ensures a Chapter 11 bankruptcy filing. It would be the largest bankruptcy in airline industry history.

Chief executive Glenn Tilton, following a meeting Thursday with leaders of the pilots' union that holds the largest single stake in the airline, declined to say whether United will file for bankruptcy but said it is not inevitable.

"What we have said is we're going to consider all of our options and nothing really is a foregone conclusion," Tilton told Chicago's WLS-TV. He said Wednesday that the airline would continue to fly whatever choice was made.

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But barring a dramatic turn of events, that course will almost certainly take it into federal bankruptcy court as soon as this week.

"We believe bankruptcy is inevitable," J.P. Morgan analyst Jamie Baker wrote in a note to investors Thursday.

"I can't imagine them avoiding it unless someone writes them a check for $2 billion," said Ray Neidl of Blaylock and Partners.

Cash-starved United has said for months that without government backing, it couldn't get the $2 billion private loan it needs to avoid bankruptcy. It faces $920 million in debt payments due next week, which would wipe out most of its cash.

Further sealing United's fate, its mechanics canceled a vote scheduled for Thursday on $700 million in wage cuts the carrier said it needed immediately to stay out of bankruptcy. Union leaders said the government board's decision had rendered the vote moot.

United's unions blasted the decision by the three-member government panel, which was created last year to help the financially strapped airline industry recover after the Sept. 11 terrorist attacks.

"We were ready to partner with United, the union coalition and the government to return United Airlines into the nation's premier carrier," said Tom Buffenbarger, president of the Machinists' union that represents the 13,000 mechanics and aircraft cleaners who were to have voted. "Unfortunately, the United States government walked out on that partnership."

United traces its problems to a decline in passengers because of the faltering economy and the terrorist attacks, an increase in competition from smaller discount airlines and failed business strategies. It has lost more than $4 billion since the middle of 2000 and is on pace for an industry-record loss exceeding $2 billion for the second straight year.

The government board said that despite United's efforts to pare costs, "the business plan submitted by the company is not financially sound."

The board said United's plan "does not support the conclusion that there is a reasonable assurance of repayment and would pose an unacceptably high risk to U.S. taxpayers."

Tilton didn't say whether the company would file for bankruptcy or file a revised proposal.

Two of the three board members rejected United's request, while the third wanted to defer a decision until Dec. 9 to allow United to submit additional financial information.

"This is not just about costs," said one member, Peter Fisher, the Treasury Department's undersecretary for domestic finance, "it's about a business plan that is fundamentally flawed."

In bankruptcy, United's shares would probably become virtually worthless and it would lose control of its restructuring to a bankruptcy judge. The airline is 55 percent owned by its employees.

The people who fuel and de-ice airplanes didn't have much to say about the latest developments.

"With (Wednesday's) news it's deafening out here," worker Rich Pijanowski said.

Still, he said union leaders have been busy talking to management, hopeful that United could meet with the panel and see what further cuts it expected from the airline.

"I think most of our group has gotten past how we got here and are more interested in how to get this thing turning in right direction," he said.

Mechanic Dan Mattingly echoed his concerns, saying it makes no sense for unions to approve cuts, only to have them rejected by the panel later.

"The money is just sitting there and they're not helping the airlines out," said Mattingly, who started the day watching on television how United's stock had nose-dived. Like many other workers he accepted wage cuts and work rule changes for six years in exchange for stock which would be rendered worthless by a bankruptcy.

Some passengers flying United on Wednesday said the government should help it stay in business.

"We need the competition to keep the fares lower," said Courtney Burkholder, 31, of Lincoln, Neb., as she walked through Chicago's O'Hare International Airport. "Generally, it seems unfair that the airlines suffered for the terrorist attacks."

Only two major airlines, America West and US Airways, have gotten help from the board. But US Airways still ended up filing for bankruptcy protection in August.

Analysts say United will emerge from bankruptcy a smaller, changed airline, assuming it emerges at all.

"If they make peace with labor, they will come out of Chapter 11 stronger than they've ever been," said Darrell Jenkins, head of George Washington University's Aviation Institute.

Other airlines have survived bankruptcy, including America West and Continental, which filed for bankruptcy twice.

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