THE PRESIDENT'S budget contains what is called a "placeholder" for the cost of the Gulf war -- a request for funds that officials acknowledge is inexact because they can't foretell the future. In fact a larger share of the entire defense budget could be regarded as a placeholder. The war's cost is not the only great uncertainty. The technical limits and possibilities it will disclose are another. What happens next in the Soviet Union is a third.

The budget continues down the path agreed to last year of scaling back the armed forces. The planned cuts of about 25 percent over five years in broad terms are larger than some of the surrounding rhetoric, particularly about the peace dividend that never was, would suggest. It's right to cut back; the threat of a land war on short notice in Europe, which drove so much of the budget before, has been reduced toward insignificance. Other kinds of threats have become more easily imaginable.

The budget hedges as to the separate strategic threat the Soviet Union continues to pose in the form of intercontinental and other nuclear weapons. A lot remain, together with a question as to who, in an unruly country, will control them. The administration thus proposes to continue modernizing U.S. strategic capabilities, offensive and defensive -- building the B-2 bomber, developing the Midgetman missile, arming (but not adding to the number of) Trident submarines and investing $5 billion a year in the possibility of strategic defense. Some of this caution seems right, some open to question. In relation to the B-2 and the Strategic Defense Initiative in particular, though no one wants to lose a good technology, what is needed is clear-eyed review, not a signal of full speed ahead.

As to the war, we now know a little about which weapons work, but not yet as much as the best-case film from the briefing centers might suggest. Definitive knowledge and how to proceed on the basis of that knowledge are a good way off. You can hear all kinds of confident analyses, but too often they conflict; the war has yet to teach what future weapons we should buy. So also as to the related question of net cost. That will depend not just on the length and intensity of the war and the contributions of other coalition members, but -- in light of the build-down that is going to occur anyway -- how much and which parts of the depleted inventory it is decided to replace, and which parts will be not so much replaced as superseded.

Maybe by late summer or fall, when Congress normally passes the defense bills, the answers to some of these questions will be clear. They aren't clear now.