The Defecit news from the Congressional Budget Office yesterday sounded better than it is. The nonpartisan office published its so- called baseline budget projections -- estimates of the likely course of revenues, spending and the deficit over the next five years if the government were simply put on automatic pilot, and Congress left current law alone. They show the deficit declining from this fiscal year's estimated $208 billion to $181 billion in fiscal 1987 and $104 billion by 1991.

That is nowhere near the balanced budget by 1991 envisioned in last year's Gramm-Rudman amendment. But it would be a large enough decline to take a lot of the pressure off. Congress would not need to cut as much, and there would be less to fear if it failed. The Office of Management and Budget made similar projections when the president sent his budget to Congress earlier this month. If the deficit is self-destructing, why the fuss?

Because of how these forecasts were made. CBO only last August was looking toward a deficit of nearly $300 billion by 1991 if nothing was done to current law. That estimate was so high mainly because it assumed the Reagan defense buildup would continue. The new estimate is so much lower mainly because it now assumes the buildup will stop, that defense spending will be increased only enough each year to cover inflation. Take away the defense buildup, which has been one of the main sources of the deficit, and of course the deficit will decline.

But that is precisely what the president has not agreed to. OMB, therefore, assumes the buildup will continue. But it also assumes the economy will perform so well that -- mostly in the form of higher tax yields and lower interest rates -- it will offset and wipe out the buildup's cost.

So there you have it. The good news is that, yes, the deficit will fade away if either the economy produces much more than expected or the president demands much less. But that has always been true. Congress faces the same choices as before. The budget office has simply rephrased them.