IN HIS Thursday press conference, the president said that in seeking ways to close the budget deficit, he might consider savings from defense. His spokesman, Larry Speakes, however, later explained that the president wasn't talking about any major scale-backs in the planned $1.6 trillion buildup, but rather some of those "management savings" that have promised so much and delivered so little to date. This means that the job of revising the defense budget is likely to fall to Congress, a result that past experience suggests will not do much for either reduction of future deficits or the strengthening of national security.

For obvious reasons, Congress prefers to spread defense money around as many districts as possible. This generally means making small down payments on a host of weapon systems. The individual military services applaud this strategy because it builds congressional support and because weapons systems are hard to stop once they are in production and jobs are at stake.

The military will also point out that cutting out new weapons starts doesn't do much for next year's deficit. That's because it takes a long time to build up production. Only 15 percent of money authorized for procurement in a given year will be spent in the same year. For shipbuilding, less than 2 percent may be spent in the first year.

The "slow spend-out" argument, however, cuts both ways. Making small down payments on new weapons now means having to cope with large uncontrollable increases in future spending as production builds up. And once the weapons are built, the budget must absorb the huge costs required to man, operate and maintain them. An American Enterprise Institute study estimates, for example, that the long-run cost of operating and equipping the 600-ship Navy now planned will be three or four times greater than the initial cost of shipbuilding.

With the economy still in the doldrums, next year's deficit may not be as important as the deficits expected if and when the economy moves into substantial recovery -- which is exactly when the big bills for current weapon-buying decisions will start falling due. When those costs become obvious, public resistance to defense spending is likely to accelerate followed by a return to the start-and-stop pattern of defense spending that has caused so much disruption and inefficiency in defense planning in the past. Needed advances in weaponry may also be blocked because available resources are tied up in producing and operating outmoded weapons.

The administration's hastily constructed defense budgets have included almost all of the weapons plans hatched during the three preceding administrations. Among them are several expensive systems that many supporters of a strong defense now criticize for being either defective in operation or out-of-date in concept. The best place for sorting out competing claims for scarce defense budget dollars--and leaving a margin of discretion for adjustments of strategy in the future -- is within the administration.

If the administration sidesteps that task and continues its insistence on hitting preordained numerical targets for defense spending, Congress is liable to do the job instead. The results would probably not produce either future budget discipline or an orderly plan for strengthening the nation's defenses.