CHICAGO – Cash-strapped United Airlines said in a bankruptcy court filing yesterday that it “likely” will be necessary to terminate and replace its employee pension plans.

The carrier cited the size of further cost cuts and the need to find bankruptcy-exit financing as reasons for such a drastic move.

The filing came a day before a federal bankruptcy court hearing on United’s pension plans, which the company announced last month it would no longer contribute to while in Chapter 11. That action has been assailed by United’s unions and challenged by the government’s pension-protection agency as violating federal pension law.

If United ends its four employee pension funds, it would represent the largest pension default ever by an airline. The action would dump billions of dollars in future pension obligations onto the already-strapped Pension Benefit Guaranty Corp.

The agency said last week that United’s pension plans are underfunded by $8.3 billion.

In its court filing, United cited the government’s recent decision to reject its bid for a $1.6 billion loan guarantee along with sky-high jet fuel prices. The airline, based in suburban Elk Grove Village, Ill., said it “must have the cash flow and liquidity that the financial markets are willing to finance.”

“We have taken every effort to restructure our business without affecting accrued pension benefits, and will continue to explore every other option,” the company said in the 26-page filing. “However, given the magnitude of further cost reductions needed to create a viable business plan and attract exit financing, termination and replacement of all our defined benefit pension plans likely will be required.”

The possibility of such a move surfaced last month when United, facing $725 million in 2004 payments to the funds alone and over $4 billion by 2008, defaulted on a payment and announced the cutoff in contributions.

Pension Benefit Guaranty Corp., a government agency, takes over failed plans and pays benefits to retirees that sometimes are substantially reduced. It insures benefits for 44 million Americans. But it racked up a record $11.2 billion deficit from covering failing plans through the end of 2003.

The court filing did not outline possible replacements for United’s defined benefit pensions.

“No final decisions have been made,” spokeswoman Jean Medina said. “We are still in the process of reviewing that.”