Defense spending is already the real subject of the SALT debate and bids fair to hold the stage through the presidential campaigns. Is it too much to hope that the discussion will become more sensible and realistic than what we've seen so far? That senators and columnists will stop pretending that the issue is whether the budget should go up by 3 or 5 percent and recognize that what really matters is the way the money is spent?

Most of the 5 percenters have shied away from specifics about just where the extra money should be used. Following the lead of Sen. Sam Nunn (D-Ga.), they refer such questions to the Joint Chiefs. But it is not difficult to guess what the extra money would buy. The "enhanced" version of the Pentagon budget is likely to contain the sort of equipment Edward Luttwak recently mentioned in an article on this page: nuclear-powered aircraft carriers; "high-performance" bombers resembling the defunct B1; newer, faster aircraft, with more electronic equipment; more and bigger ships; more "precision" weapons to use against planes and tanks. Somewhere on this list come training, transport and spare parts, but the real money is likely to go for big-ticket hardware purchases.

Maybe this will turn out to be just what we need to improve the nation's defense. But is it not equally possible that we'll get less real defense, at greater cost? There are several questions I wish the 5-percenters would answer before we spend more money in the same old way.

1) How much is all this really going to cost? Within three years, from late 1971 to late 1974, the estimated cost of the B1 bomber quadrupled, from $25 million apiece to $100 million (including the effects of inflation). Why should we expect anything different from the MX missile? The administration originally estimated the total cost to be $30 billion. Already, some Pentagon offices are using $55 billion -- without any adjustment for inflation -- as a working figure.

2) What about the feasibility of keeping these systems running once we get them built? Don Cook recently pointed out in The Los Angeles Times that landing the proposed new 110,000-man "mobile intervention" force would be a larger undertaking than the entire Allied invasion of Normandy, not to mention such details as finding water for 110,000 men in the Arabian desert or keeping machinery running in the sand and heat. "We have our combat aircraft down about 50 percent of the time, because of their sophistication," Sen. Gary Hart (D-Colo.) recently said. The more complex the weapons system, the worse the problems of maintenance and reliability are.

3) Even when they're running, will these weapons really make a difference -- not on the test range, but in the real circumstances of war? Military designers are well pleased by a new generation of "Precision Guided Munitions," such as a missile called TOW. A soldier stands and fires a TOW at an enemy tank; by keeping the tank in his sights, he can adjust the course of the rocket in flight, theoretically ensuring a hit. But those familiar with TOWs say that, to guide them, a soldier must stand exposed from the waist up for about 10 seconds, virtually ensuring that he'll be hit himself. This spring, a weapons designer named Ori Even-Tov explained in Orbis that precision weapons can be catastrophic failures against an enemy who understands how easy they are to jam. Many precision weapons rely on optical guidance or infrared detection systems to find their targets and require clear daylight conditions to work. This is fine for tests in the Nevada desert, but not for the smoke, dark and fog of the European battle plain.

4) Does our spending respond to realistic threats? The MX missile system is based on the premise that one side's nuclear missiles can destroy the other side's missiles in their silos. The MX is supposed to be accurate enough to pose that threat to the Soviet Union and mobile enough to prevent the Soviets from doing the same. When we hear a senator speak of a Soviet missile with "accuracy" of 175 yards, we assume it could come within 175 yards of an American silo, close enough to score a kill. But "accuracy" is only a measure of consistency; if you fired two dozen of those Soviet missiles and drew a circle containing half the impact points, the radius of that circle could be its "accuracy" (or "Circular Error Probable"). To know whether any of the missiles came close to waht it was supposed to hit, you would need to know the "bias," which is the distance between the target and the center of the impact pattern. Bias is caused by unexpected winds, gravitational anomalies and countless other irregularities, and it is different for each flight path. When missiles are sent over a certain path time and again, the bias for that path can be eventually worked out. But no missile has ever flown the path that Soviet or American missiles would take in a nuclear attack. Nearly every missile designer and tester is aware of bias; somehow it has totally escaped the public debate.

5) Does the focus on complex hardware blind us to some of the graver problems with our defense? For 20 years the career service has adopted the ethics of the businessman rather than the warrior; in Vietnam, careers were made while the war was lost. Our military doctrine is based on the days when we had crushing logistical superiority over all foes and did not need to concentrate on innovation or maneuverability; now we are the smaller force. Effective military force has historically depended on a combination of ideas, motivation, training and equipment. Now we concentrate on the machinery alone.

We're not the first to think that more money will buy better defense, no matter how it's used. In the 1930s the French made major sacrifices in the name of strong defense. By the end of the decade, their hardware was unrivaled on the continent: they had more tanks than Hitler; they had poured their treasure into building the Maginot line. All the Germans had in their favor was the idea of blitzkrieg war.