Even if the budget cuts finally agreed upon by Congress call for relatively small reductions in defense, the cuts could have large implications both for future budgets and for the nation's security. Because of the time it takes to develop most weapons systems, decisions on what to order now can translate into important differences in combat capability and spending requirements in the "out years."

This fact pushes Pentagon planners, when faced with the threat of budget cuts, to protect those relatively small immediate expenses that represent down payments on big future weapon purchases. Reductions are then concentrated on recurring costs for operations, maintenance and the other low-visibility items that determine the readiness of existing forces.

This is an understandable reaction but, in the current situation, a dangerous one. Future spending requirements are as important as next year's outlays. There is no gain--and potentially much loss-- in starting to produce weapons that you can't afford to buy, operate and maintain in the future. The Reagan budget calls for an inflation-adjusted rate of increase of about 16 percent a year in obligations for weapons development and procurement. It is by no means clear that this buildup is either within the capacity of the defense industry or compatible with the manpower resources available to operate and maintain the weapons produced. Even at that, some military planners estimate that what is really needed to meet the administration's general strategic objectives has been substantially understated.

There is no way to make a definitive assessment of the military dangers the nation faces. Nor--if there were--would there be any automatic method for translating such an assessment into a description of needed forces and the budget requirements to buy and maintain them. But hard choices need to be made, and the administration has thus far sidestepped those choices by embracing a strategic concept so broad that it can justify almost any new weapon start sought by the military.

Congress has been asking increasingly sharp questions about the implications of the administration's defense plan--but it hasn't been getting many answers. If Congress is unable to give the defense budget the thorough review that it needs before this year's budget decisions are made, the nation may find itself buying a defense establisment that is not only very costly, but unready to respond to real threats in the near future.