"FASBY," to use the informal name for the powerful private Financial Accounting Standards Board that is the keeper of the American definitions of profit and loss, has issued a new accounting rule that will sharply reduce the net income and take billions of dollars off the balance sheets of many of the nation's larger corporations.

It's a good idea -- that companies when they report their income and net worth recognize the full future cost of any health benefits they have promised their retirees, a liability now only fractionally recorded. When the rule begins to take effect in 1993, investors will have a better idea of what they may be buying.

But the higher level of truth leads to a series of public policy questions. The reason FASB issued the rule is that these costs are turning out to be greater than had earlier been understood. When larger companies began providing such benefits about 20 years ago, the habit grew up of paying and accounting for them on a current or cash basis. Now inflation and the steady aging of the population have so driven up prospective costs that, in the eyes of the accounting standards board, this is no longer fair. Companies will be required to estimate and show their full liabilities and reduce their reported earnings enough, over time, to finance them.

But if this is such an important cost that the money needs to be set aside in financial statements, isn't it also important enough that the money should be set aside in fact? An accounting question leads to a social question: Should Congress do here what it does with pensions and require that companies build up reserves to finance future benefits? The social question becomes a tax question: If Congress does require such buildups, mustn't it also in fairness make the payments deductible, as pension payments are but advance health care payments currently are not? The tax question then raises fiscal and regulatory issues. If Congress does make such payments deductible, where in the present fiscal circumstances is it going to find the money without increasing the deficit? And will just any future health benefits qualify for deductions, or only such kinds as Congress approves? What might be the rules?

Accountants don't normally drive health care policy. But here they are forcing both companies and indirectly the government to confront in still another form the question of how much health care for whom, and at whose expense, is the society ready to provide. Good for Fasby.