WASHINGTON (Reuters) - The Bush administration expressed fresh concern on Wednesday about the possibility bankrupt United Airlines might scrap its employee pension plans, which would shift the burden of paying benefits to the government.

In a rare outreach to organized labor, White House, Treasury and other administration officials met with leaders of the International Association of Machinists. They discussed the airline's decision to suspend pension contributions during restructuring, union and administration officials confirmed.

Additionally, the meeting covered growing speculation among industry experts, labor groups and others the No. 2 carrier is preparing to dump its four underfunded employee retirement accounts that cover 120,000 active and retired workers and let financially pressed federal pension insurers assume the obligation.

The Pension Benefit Guaranty Corp. insures private retirement accounts for 44 million people.

The central concern is that a move by United to scrap its pensions could prompt other struggling airlines to do the same with their underfunded accounts. That scenario could bankrupt the PBGC and trigger a taxpayer bailout much like the one approved by Congress for the savings and loan industry more than a decade ago.

"We are concerned about the United pension plans and are listening to the ideas of the machinists and others," said Claire Buchan, a White House spokeswoman.

A United spokeswoman, Jean Medina, said the airline has made no decision about the future of its pension programs but has met and will continue to meet with union leaders on the option of negotiating changes.

POST-BANKRUPTCY FINANCING

United missed a $72 million payment this summer and suspended two due this fall totaling nearly $500 million to give it more financial flexibility as it tries to lure investors for post-bankruptcy financing.

The government estimates that United's pension plans are underfunded by $8.3 billion.

The PBGC has no authority to make United make its pension payments or prevent it from scrapping those plans, and it is unclear what the White House or other agencies can do to mitigate the threat.

The airline has already agreed to appoint an independent legal overseer to represent employee participants in pension programs. The selection must be approved by the Labor Department.

But a source with knowledge of Wednesday's meeting said administration officials were considering other steps to hold United accountable. "I don't think they will let United Airlines just walk away and leave the government holding the bag," said the source.

To reduce its pension obligations, the airline must either negotiate new concessions with its unions or convince a federal bankruptcy judge that it cannot survive without eliminating one or more of those plans.

US Airways terminated its pilots' plan before exiting bankruptcy in 2003.

The machinists, which sued United over the suspension of pension contributions, are hopeful the administration will at least pressure the company to consider other cost-saving measures.

"United Airlines has made a serious mistake if they think the federal government is going to willingly accept pension responsibility from companies abandoning their obligations," said Robert Roach, IAM vice president.

The IAM represents more than 20,000 customer service agents and ramp workers at United.