EVER SINCE President Bush announced his willingness to undertake "preemptive" or "preventive" wars, the chorus has grown of those who insist that war must invariably be the last resort. At the core of this argument is the conviction that war is terrible and, therefore, ethically unjustifiable unless it is the only way left in which to pursue an important aim. The preferred method, of course, is diplomacy, but there are many who would argue that economic and other sanctions are more justifiable than war and must have failed before war can justly begin. There are a number of practical objections to this belief, but they are not the chief objections. For it is frequently the case--and clearly so with regard to Iraq today--that waiting until all other avenues have been exhausted is unethical.

In almost every crisis that leads to war there comes a point at which it is plain that war is likely. At that point, both sides begin to consider what preparations they need to make to go to war, and often they begin those preparations. The warrior's art includes recognizing the moment at which an attack would carry the maximum likelihood of success. If we allow our soldiers to strike at that moment, we give them the ability to take the enemy by surprise, attacking him at a time or in a place or manner for which he is unprepared to respond. Surprise creates the conditions for successful military campaigns. The casualties are generally lower for both sides, moreover,

If, on the contrary, our military is required to wait on an open-ended basis while diplomacy and other avenues are "explored," the likelihood of achieving surprise is dramatically reduced. What is more, the enemy is given time to prepare himself to fight, digging into defensive positions, pre-designating targets for strikes by artillery, missiles, or weapons of mass destruction, training, stocking up on supplies, and so forth. As time goes on and the enemy observes our own military preparations, he gains an ever fuller understanding of what forces we intend to bring to bear and how we may use them.

Another problem with waiting for diplomacy to fail is that soldiers, sailors, and airmen cannot maintain the highest level of war-readiness indefinitely. There is a psychological dimension to this problem, in that daily expectation of an event that does not come is both exhausting and numbing. There is also a practical dimension. Soldiers, sailors, and airmen who are standing by for an operation are rarely able to continue full-scale combat training. Without that training, their combat skills begin to degrade. Every day that goes by after the best moment to strike has passed and before combat begins is likely to degrade the combat capabilities of our troops.

The result is that we provide the enemy with a much greater ability to hurt us. And that hurt is measured in the lives of our troops in the field lost because of delay in the attack. To be sure, if there is a prospect that diplomacy might succeed, the likelihood of that success must be weighed against the probability that more lives will be lost if war is delayed. The ethics of the situation thus are less clear cut than proponents of "letting diplomacy take its course" like to claim.