When is the budget deficit like the weather? When it's forecast

Are you tired of hearing about federal deficits? Do all those huge numbers jumble together in your mind? Do you secretly believe that much Washington argument about the problem is meaningless, a debate over how many economists can dance on the head of a pin?

Don't feel bad. You are probably not alone. Over the last three years, predictions of the size and effect of deficits - from politicians of all stripes - have been characterized by wild inaccuracy and shifting points of view.

Many Memorable Moments in Deficit History are rich with irony:

* Treasury Secretary Donald Regan, at his confirmation hearing in 1981, casually remarked that the budget would be balanced in 1984. This caused more controversy than he anticipated, and at a subsequent appearance he hemmed a bit and said yes, he had been wrong: The budget would be balanced in 1983.

* David Stockman, in his first appearance before a congressional panel, devoted most of his testimony to sneering at President Carter's inaccurate budget figures. Soon after, the Reagan administration said the 1982 deficit would be $27 billion. It turned out to be $110 billion.

* Larry Speakes, White House spokesman, last week lambasted Council of Economic Advisers chairman Martin Feldstein, whose dire warnings about deficits have irritated the White House.

But it's the White House whose attitudes have flipped, not Feldstein's. During 1981, administration officials routinely predicted that big deficits would lead to high interest rates and skyrocketing inflation.

Today's official administration position on deficits (roughly paraphrased as ''they're awful in a theoretical sort of way, but we can live with them for now'') didn't appear until the end of 1981, when Murray Weidenbaum, then chairman of the Council of Economic Advisers, floated it at a public meeting of economists.

But Republicans aren't the only ones whose deficit pronouncements have at times seemed miles wide of the mark.

The Congressional Budget Office's initial prediction for the '83 deficit, made in 1981, was $17.7 billion. When the books closed on fiscal '83 this fall, the final shortfall was just shy of $200 billion.

Democrats on the Joint Economic Committee (JEC) did somewhat better. They predicted the deficit would be $100 billion, by 1984. But at the same time, the JEC said that interest rates would stay very high (they haven't) and that inflation would not nose-dive (it has).

The factor that threw off all these figures, of course, was the recession. In one sense, economic forecasting is like weather prediction: When you do it far in advance, something you didn't count on will invariably intervene. If your forecast is short-term, you'll be more accurate.

By the time the economy hit bottom in 1982, it was clear the deficits would be big enough to make King Kong look like a chipmunk. Since then, many politicians - mostly Democrats - have made dire warnings about the deficit's effects which haven't come true.

House Budget Committee chairman Jim Jones (D) of Oklahoma, for instance, said in February '82 that deficits would ''frustrate recovery.'' The latest economic indicators show that the recovery continued to step along smartly in October.

All this ''rhetoric inflation'' may be one reason the public seems to view deficits as an abstract threat, instead of a dire one. The average voter does think deficits are bad: 90 percent of respondents to a Harris poll this summer said budget shortfalls were a serious problem.

But congressional aides say the deficit isn't yet a hot political issue. So far, they say, voters are far more likely to be swayed by the effect of the recovery on their own budget deficits.

Indeed, public approval of Reagan's management of the economy, as measured by polls, has risen with the recovery - even though the White House this year has refused to lead an attack on the deficits.

And without strong public support, Congress is unlikely to mount a charge of its own, since solutions to the problem tend to be unpalatable.