NEW YORK (CNN/Money) - You've built up this asset over the years.

You expected it to be there in the future to help with emergencies, your retirement or maybe just a vacation at some point in time.

Now you're worried that it may become worthless, but the rules that control it prevent you from selling it now so you're not wiped out.

That Enron employee-like dilemma is faced by many of the 40 million members of United Airlines' Mileage Plus program, its frequent flier program that could become worthless if the bankrupt carrier is forced to halt operations.

A halt of operations at United is apparently not imminent, but the airline is struggling to meet certain cost-cutting goals required by its lenders. Airline spokesman Joe Hopkins said the airline is concentrating on winning union and court approval of a plan to become profitable once again, not possible liquidation. The airline won't comment on what would happen to its mileage program if it is forced to stop flying.

Still, many airline analysts worry that U.S.-Iraq war could dry up already sharply reduced demand for air traffic and further drive up fuel prices, the airline industry's second greatest cost after labor. That could plunge a number of airlines into bankruptcy and could mean the end of United. Three major carriers -- Eastern Airlines, Pan Am and Midway Airlines -- halted operations in the wake of the 1991 Gulf War.

Rules governing United's program and those at other major carriers' prevent the miles from being sold or bartered, or combined with another person's account. But a Mileage Plus member can book travel for another person using their own miles. United spokeswoman Chris Nardella says the airline monitors online auction sites to make sure there isn't bartering or sale of miles going on in the open.

"A member can lose their privileges if they are selling or bartering miles," she said.

The potential loss of United miles is causing worries for many of its members, said David Stempler, president of the Air Travelers Association.

"People are really panicking," said Stempler. "All I can tell them is they shouldn't worry too much about it, that they have to remember to some degree they really didn't pay for the miles."

But while the miles can't be sold, there are alternatives to sitting by and seeing the miles disappear if United if forced to halt operations.

The miles can be exchanged for Hilton Hotel Honors Points and or points in Diners Club's "Club Rewards" program. There are no limits on those exchanges. And those points can then be converted into some other airlines' frequent flier miles. But Randy Petersen, editor of Inside Flier magazine, said that double conversion can cost a member between 30 to 70 percent of their miles. He'd recommend against the conversion.

"I don't think the situation is that dire yet," he said. "While those options are out there, look before you leap."

Another protection is to book tickets on United sometime before Feb. 19, 2004. Even if the airline is force out of business before then, a federal law passed in the wake of Sept. 11 requires other carriers on the same route to honor that United ticket for no more than a $25 rebooking fee.

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That ticket will likely be honored on a standby, not confirmed, basis, though. And Petersen said it's not clear whether frequent flier tickets will be honored by other carriers under the regulation, although the DOT language speaks only of "passengers ticketed for air transportation on that route" rather than those holding revenue tickets. DOT spokesman Bill Mosley said the question of frequent flier tickets being honored has not been determined one way or the other yet by the DOT.

Even if such tickets are honored, Bestfares.com President Tom Parsons said it is important that a holder of a United ticket keep a printed confirmation of the reservation if they are going to hold an e-ticket. A paper ticket would be added protection, although United and many other airlines charge extra for an paper ticket today.

If the ticket is not used, and United is still in business at the time of the travel, the holder of the ticket has up to a year to use it, or it can be converted back into miles for a $75 fee.

If a Mileage Plus member wants to take a trip and not be stuck on standby, they can book a ticket now on one of the two dozen other airlines that accepts United miles for travel.

There are three domestic carriers that accept the miles -- Delta Air Lines, the nation's No. 3 carrier, U.S. Airways, the No. 7 carrier which, like United, is operating under bankruptcy court protections, and Aloha Airlines. In addition there are 21 overseas carriers that accept United miles.

Those carriers are likely to continue to accept the ticket purchased with United miles even if the carrier has halted operations. But they are unlikely to accept United miles in reservations made after a halt of operations by United, said Tom Parsons, president of BestFares.com.

Some airlines that have ceased operations in the past have been purchased and their frequent fliers have had their miles folded into the acquiring airline's program. But with the weak state of the industry, it is unlikely any other carrier will have the wherewithal to buy United.

Parsons and airline consultant Jim Craun of Eclat Consulting said it is unlikely anyone will buy United's Mileage Plus program with the liability for future flights. United's most recent annual report stated that it expected miles held by customers at the end of 2001 to result in 9.1 million round-trips, and booked a $644 million liability for that expectation. More recent figures have not yet been released by the airline.

"Frequent flyer miles and programs are seen as a necessary evil," said Craun. "If they want to woo United customers, they would do it with their own programs, not by buying United's program."

Parsons said that the top-tier Mileage Plus members, the business travelers with about 100,000 or more miles, could be wooed with offers by other carriers like American Airlines.

"The guy who takes three years to get to 25,000 miles, American could care less about him," Parsons said. "American may kiss up to the super elite member, but that could also be limited, they may honor his miles up to so many miles."