That erratically recurring hallucination, civil defense, has at last appeared in the Carter administration. But the outbreak is mild, with sypmtoms limited to a pre-SALT gesture to the bunker-mentality crowd that was laughed away when John F. Kennedy advised all Americans to start digging.

At that time, talk-show itinerants earnestly debated the ethics of prudent shelter builders shooting slothful neighbors who begged for cover. It was recommended that those without a backyard could improvise protection against the hydrogen bomb by stacking books around a dining room table and crawling inside. And, to the probable bafflement of archeologists some centuries hence, billions of vitamin-enriched biscuits and a lot of canned water were squirreled away. But, for all its toleration of foolishness, the American body politic does not long endure absurdity; civil defense never flourished.

What has survived under the label of civil defense, however, is a cut-rate skeleton bureaucracy that's mainly confined to periodically setting off sirens that no one understands.There's also a contingent of think-tank hardliners that feverishly contends that the Soviet Union - despite its notorious inability to house its people satisfactorily above ground - has accomplished the extraordinary feat of providing them with emergency housing below ground; or that, with its creaky transport system, the Soviets can swiftly evacuate its cities to prepared sites in the famously hospital Russian countryside. Skeptics who have failed to come upon this necessarily prodigious system during residence or extensive travels in the Soviet Union are advised that you only have to know what to look for.

In any case, the dig-in school of civil defense has been suceeded in the United States by advocates of a new approach - evacuation, which calls for rapidly emptying out areas that are considered attractive targets. How, to where, and with what means of sustenance when they get there is not stated. Nor is any help offered with another puzzling matter, namely: that the new pinpoint accuracy and high yield of Soviet missiles makes it mandatory for the United States - in the opinion of the hardliners - to replace deeply sheltered missile silos with a mult-billion dollar mobile system; but, at the same time, mass evacuations are to take place through the easily wrecked bottlenecks of bridges, tunnels and cloverleafs that routinely gum up commuting in most metropolitan areas.

As announced last week by the administration, the new step incivil defense calls only for moderately expanding the planning of evacuation plans - no more than that. Money, of course, is the measure of intent, and what is note-worthy is that the administration is not aiming high. For fiscal 1980, total civil-defense spending would rise from the present $100 million to $143 million; and over five years - Congress willing, which is doubtful - total spending is projected at a maximum of $2 billion, a piddling sum for making ready to evacuate scores of millions of people.

Strategy scholastics on both sides of the civil-defense issue are now provided with a new occasion for exotic speculations on what the Soviets might conclude if they do this and we do or don't do that, and vice versa. Like much else on the periphery of Soviet-American antagonism, civil defense can be a living for members of thinking class.

However, as distinct from all other strategic matters, civil defense requires the attention and bodily cooperation of the citizenry, a factor that turns out to be the saving impediment. In an era of precision-guided, multi-megaton weapons, civil defense makes no sense and is easily seen to make sense. Which is why it has languished throughout the atomic age and is likely to continue to do so.