ALL WAS gloom and doom when Health and Human Services Secretary Richard Schweiker and budget director David Stockman appeared before the House subcommittee on Social Security. According to Mr. Stockman, reforms like the ones the administration proposes must be adopted or "the most devastating bankruptcy in history will occur on or about Nov. 3, 1982."

This sort of hyperbole, with its pointed reference to the timing of the next elections, is no doubt a useful goad to congressional action. It is not, however, an accurate picture of the peril that Social Security faces over the next few years. To get a better idea of the real situation, you need to remember a bit about how Social Security works. While every contributor to Social Security does, in fact, have an "account" in which records of his contributions are kept for use in computing future benefits, no separate fund is kept for each potential beneficiary. Instead, payroll taxes collected each year are used to cover benefits paid out in the same year. Only a small cushion -- commonly but inaccurately referred to as a "trust fund" -- is kept on hand to cover unexpected fluctuations in revenues or benefits.

This means that Social Security can't really go "bankrupt" the way a private insurance company can. The worst that might happen is that income plus reserves would fall short of benefit obligations in a given month. If no action were taken to cover the gap -- such as borrowing from general revenues or raising payroll taxes -- checks could still go out, but not in the full amount owing. In future months, more taxes would come in and more checks could be written.

Even a temporary reductions of benefits is not, however, an acceptable contingency for a system as important as Social Security. For this reason, the administration and Congress are right to worry about the fact that the retirement part of the system is right now dipping into its reserve kitty at the rate of about $10 billion a year. In a year or so, the reserve will be exhausted, and revenue will not cover obligations. This shortfall, moreover, is likely to continue until sometime in the next decade.

Bear in mind, however, that, relative to the size of Social Security, we aren't talking about a very big gap. Under the cheery economic conditions that the administration expects its economic program will bring, nothing more would be needed than some temporary loans from the now flush Medicare fund. The administration wants to reduce benefits by as much as $110 billion over the next five years only because it wants to build up a substantial reserve, increase benefits to people who are still working, cut payroll taxes slightly and cover the possibility that the economy will get worse instead of better.

With a more plausible forecast, no benefit increases and a more modest reserve, savings of about half that amount would do. That's still $10 billion a year, but with no adjustment, Social Security will be paying out over $160 billion in cash benefits next year. In other words, we are talking about a potential cash deficiency of about 6 cents on the dollar. That's worth treating seriously. But it doesn't rank among history's great calamities.