The government's pension insurance agency yesterday objected to United Airlines' failure to make legally required payments to its pension plans and demanded to know how the airline intends to meet its obligations as it seeks to emerge from bankruptcy.

If UAL Corp.'s United cannot make these payments -- and its plans were underfunded by some $7.5 billion when it filed for protection from its creditors -- it could persuade the court to allow it to terminate one or more of them, as US Airways Group Inc. did, in order to emerge from bankruptcy.

United did not make a required quarterly payment of $72.4 million on July 15 and has said that its bankruptcy funding agreements bar it from making such payments.

However, termination of its plans, while triggering government insurance, would have a heavy impact on the airline's workers. When the government's Pension Benefit Guaranty Corp. takes over a plan, it limits pensions to a maximum of about $44,000 a year at age 65, far lower than many United workers, particularly pilots, are expecting.

United spokeswoman Jean Medina said the airline has not yet made a decision on whether it will terminate its plans.

"We have not made any decision," Medina said. "It's incumbent on United to study all of our options to sustain this burden and still attract exit financing."

In a letter to United chief executive Glenn F. Tilton, the government agency took issue with the airline's plan to curb its pension payments. "The company has characterized certain covenants" in its bankruptcy financing as "'effectively' prohibiting further pension contributions prior to exit from bankruptcy. Any such covenants would be inconsistent with [the Employee Retirement Income Security Act] and the Internal Revenue Code and contrary to public policy," PBGC Executive Director Bradley D. Belt said.

Belt noted that United owes more than $500 million in additional pension contributions this year and $4 billion over the next five years. "Therefore the PBGC would like specific information regarding how UAL intends to close the growing funding gap in these plans," Belt said.

"On the other hand, if UAL intends to terminate any of its . . . pension plans, the PBGC and plan participants should be made aware of that as soon as possible," he said.

United is "caught between a rock and a hard place," said airline analyst Raymond Neidl of Blaylock & Partners LP. Investors and lenders want to see the airline preserve as much cash as possible, but if it is forced to terminate its pension plans, that would further alienate its employees, he said. That in turn could be detrimental to United's prospects, since commercial aviation is heavily dependent on customer service.

"If they terminate their plan, that's going to make them very upset and make it much harder for their employees to work with this management or any other management," Neidl said.