(MONEY Magazine) – The specter of a corporate restructuring or takeover where you work may leave you feeling decidedly insecure not only about your job but also about your retirement benefits. Your jitters are justified, alas, especially if you hope to retire early. While you will almost certainly receive your vested pension funds at retirement, there's no guarantee that you will collect other pledged fringe benefits. By law, companies that offer traditional defined-benefit pension plans fund them in advance so the cash will be available when employees retire. Another safety net is the Pension Benefit Guaranty Corporation, a federal agency created to make good on shortfalls when pension plans run out of money. But the PBGC guarantees pensions of up to only $22,909 a year. So if you plan to retire early with a larger pension, you might not get every penny. The PBGC does not guarantee a single penny in defined-contribution plans like 401(k)s and profit-sharing programs, however. Though your company can't set back its early-retirement date for current employees or take away any vested benefits, it can tinker with its pension formula. And firms with financial problems often do, curbing pensions for future staffers expecting to retire early. Usually, however, current employees, especially those close to retirement, can choose between the old and new pension rules. The most serious pension threat occurs if your employer sells out to another with a less generous plan. Robert Liebross of the Pension Rights Center in Washington, D.C. says a merger can whipsaw employees on the verge of early retirement. Consider, for example, a 53-year-old man who worked 28 years for a company that pays full early-retirement benefits to 30-year veterans age 55 or older. If his firm was acquired by another that pays unreduced pensions only to employees over 60, he might have to wait seven years, not two, for the same retirement check. Companies aren't required to put aside money to finance health insurance coverage for retirees and probably won't have to in the future. But under an impending accounting rule change that will likely take effect in 1991 or 1992, corporations will have to start listing their future health insurance costs as current liabilities. That would add as much as $2 trillion in red ink to the nation's corporate balance sheets, according to a congressional study. Businesses of all sizes will almost certainly soon begin limiting their health-care coverage for former employees. Retirees under 65 are especially vulnerable. Steven Ferruggia, of the employee-benefits firm Buck Consultants, says, ''It's clear from the changes that early retirees are the ones who will end up paying a lot more for their own coverage.'' The reason: their insurance isn't supplemented by Medicare, making it considerably more expensive for employers. The annual cost of a health plan for a retired couple under 65 ranges from $2,800 to $4,000, compared with $1,200 to $2,000 for a couple over 65. But aren't companies obligated to finance your health insurance in retirement if they vowed to provide it? A dozen court decisions have split fairly evenly on the question. Most collective bargaining agreements include escape clauses that let businesses alter their insurance coverage, and the courts have ruled based on the precise language in each contract. Says Christopher Mackaronis, an attorney with the American Association of Retired Persons: ''Until the Supreme Court gets involved, there aren't any clear guidelines to tell current employees whether their health coverage in retirement is guaranteed. For now, you are probably better off assuming that it isn't.'' A Supreme Court decision is not expected prior to the early 1990s. -- G.A. Jr.