What a difference a year makes. In making their annual report last year, the trustees of Social Security noted that the gloomy official economic forecast made it likely that the retirement and disability trust funds would move into the red for the next several years. A long-term deficit was likely to crop up in the next century, they added. Reaction? Almost none. This year, however, the trustee's report bearing essentially the same message has created a storm.

One reason for the difference, of course, is that 1982, the time when the red ink will first appear on the ledger, is now almost upon us. The trustee's report, however, has also acquired considerable political significance for the support it lends to the administration's drive to make substantial permanent reductions in Social Security benefits.

The only really new item in the report is official recognition that, thanks to sharply rising hospital costs since the demise of the Carter adminsitration's campaign for cost containment, the Medicare trust fund is headed for deep trouble a few years hence. This is a serious matter, but it is nto on the administrtion's immediate agenda. With regard to retirement and disability benefits, the target of the administration's proposals, the biggest change is in format -- five alternative economic forecasts instead of the usual three in order to cover the rosy scenario the administration uses in justifying its tax cut program and the dire forecast it used earlier in justifying its Social Security cuts. a

For the long run, if you average the two intermediate forecasts you get, essentially, last year's forecast. This tells you that -- if birth rates stay low, longevity continues its recent rapid improvement, immigration returns to legal levels and the economy grows modestly but steadily -- about 25 years from now receipts will fall short of benefits and stay that way for quite awhile. This is worth considering in charting the system's future path, but, given the uncertainties involved, it is no cause for soundign the general alarm.

In the short run, however, the report confirms the many other predictions that, even with borrowing among the funds and the cuts already included in the budget package, additional measures are needed now to protect the system against likely continuation of the high inflation and lagging wages that have caused its current embarrassment. But this is no cause for hysteria either. Payroll taxes will still flow into the trust funds, and checks will still go out. Other trust funds -- unemployment insurance funds in this country, Social Security funds abroad -- have faced shortfalls, and the worst that happened was that general revenues were needed to fill the gap.

The administration, however, with its commitment to big income tax reductions and a balanced budget by 1984, cannot be expected to accept this way of muddling through. It would also like to have a healthy surplus in the trust funds by 1984 to offset deficits elsewhere in the budget -- as Democratic senators were quick to point out in hearings this week. Further increases in payroll taxes will also be strongly -- and rightly -- resisted by its business constituency as a jolt to inflation and a drag on employment growth. This means that some way of restraining benefits must be sought -- preferably one that avoids abrupt and unnecessary restructuring of basic benefits, spreads the losses fairly and covers the contingency of a continuingly sluggish and inflationary economy. Setting limits on cost-of-living adjustments is the only method we know of that fits this bill.