YOU PROBABLY noticed the Treasury's announcement that the federal deficit for fiscal 1982, ending last month, was $110.7 billion. There's nothing startling about that number. A large deficit, in the trough of a long and severe recession, is predictable and proper. But it illustrates the dilemma confronting the people who make policy. Big deficits tend to keep interest rates high, prolonging the recession and discouraging economic growth. But the only practical way to close the deficit is by raising taxes, and higher taxes also retard economic growth.

The past year's deficit would be less disquieting if it did not appear to be the beginning of a succession of very large ones. The administration's original estimate last February of the deficit for the year now beginning was $91.5 billion. In the midsummer review, the figure was up to $115 billion. When the next budget comes out three months from now, it will probably be up around $155 billion -- and that assumes a recovery beginning in the spring.

What accounts for this drift in the numbers? Over the past several years, it's been the consistent habit of people in official positions -- the Carter administration, toward the end, as well as its successor, and Congress as well as the White House -- to use implausibly favorable economic forecasts. Most of the budget numbers since the beginning of 1980 have been based on official predictions of performance that lay far beyond the limits of probability.

It's not merely the difficulty of foreseeing recessions with precision. It is as though public officials found it impossible to bring themselves to use the estimates that most other people consider realistic. The implications, particularly in terms of taxes, are too painful to be contemplated. In that respect, the rising deficits reflect this country's reluctance to come to terms with the budget shortfall and, more important, with the probability that the world has entered a prolonged phase of economic growth much slower than that over the past generation.