United Airlines announces its plans to balance its budgets by raiding the pensions on which its workers are depending for retirement: United Airlines said today that it was likely to terminate and replace its four employee pension plans with less-generous benefits, a drastic move that the airline said was necessary to attract the financing that would allow it to emerge from bankruptcy. In a 26-page filing with the United States Bankruptcy Court in Chicago, United stopped short of actually ending the plans and said it had not made a final decision to do so. But the warning from the airline was the sternest threat yet of its intention to shed its pension obligations. United's unions had no immediate comment. United's move came on the eve of a court hearing, at which Judge Eugene C. Wedoff planned to hear motions from the federal pension agency, United's machinists and its flight attendants challenging the airline's efforts to get out from under its pension liabilities.