A handful of Medflies turned up in Los Angeles last week. Three had already been sighted in Florida. Oakland was next. Official planes and choppers took to the air to combat the dread, elusive foe. I am aware that this combat involves aerial spraying, not aerial dogfights of the late-night-movie, battle-of-Britain kind. But I can't help it: each time a newscast or wire-service story reveals that our aircraft have once again scrambled, my mind at once fills with Spitfire images, encounters between a madly maneuvering fruit fly and a madly maneuvering fighter plane --rat-a-tat-tat gunfire, gushing black smoke and one of them spiraling crazily toward earth. Mostly I am waiting for word that the B52s have joined the fray--it can only be a matter of time. "We had to destroy California to save it," an expressionless spokesman will tell us on the 6 o'clock news one night. ("Well," we will sigh, "these things happen.")

I will leave the argument over pesticides, alternative measures and who should have done what when to the experts. My sole intention here is to nominate the Mediterranean fruit fly as symbol of the year--or perhaps of the decade. It is the perfect embodiment of our assorted miseries and dilemmas, an ideal candidate for Miss National Torment of 1981. For as a representative problem, the Medfly has it all: (1) it is a serious and genuine problem that needs to be dealt with, but (2) there is something wrong with each of the ways of dealing with it, something that involves not just certain costs and disadvantages but also (3) uncertainty as to whether the remedy will even work in the long run, as it seems to be once again (4) a too- cumbersome and too-clever technological solution, a kind of overkill that doesn't kill what you want to kill at all, another of our impressive, giant engines of frustration.

This is no doubt what has filled my head with images of mismatched weaponry and whining insects outsmarting all manner of electronic gear. But I have something more than hardware issues in mind. Surely this also describes the familiar relationship of the hardcase social or economic problem to the massive machinery government assembles to overcome it--machinery that in its ponderous way seems often to "solve" the problem at hand by reducing the whole terrain in which it exists to rubble.

The controversies going on about government regulation, whether for the purpose of protecting health or preventing an injustice or furthering some other generally accepted national goal, owe much to this skewed relationship. So does the widespread public impulse to revoke or let die legislation that has come to seem overreaching and excessive in relation to the amount of good it does. And so --in another realm--do the doubts now being expressed by some of the hawkiest of the hawks concerning the potential usefulness of certain superweapons the president is being urged to build.

Reagan came to office with a pretty clear and well-known view of this over-all situation. Except in military matters, he seemed to favor a let-nature-take-its-course approach, the exact opposite of the leave-nothing- to-chance school of social planning that had created the worse along with the better government programs in the first place. His response to the "do everything" theory of government appeared to be "do nothing." At least that was the message at the outset when we heard how a wide variety of federal interventions were going to be stopped once and for all. Better to dismantle the overkill machine, to call off the sortie altogether, than to conduct so wasteful and inefficient and troublemaking an operation. People could live their lives healthily and fairly and productively without all that burden and claptrap.

This reaction seems to me no more helpful than the overprogrammed, hyperintrusive kind of legislating and managing it finds so abhorrent. And it has naturally raised all kinds of suspicions that it is not so much the stultifying evils of a big clumsy government machine that the administration is seeking to curb as the legitimate claims of people whose hardship costs others something to fix--the poor, the disenfranchised, the exploited and abused. Interestingly, this administration, which has been unusually faithful to its pre-election, campaign-promise word, has lately shown at least a few signs of adjusting its perception of all this. In certain civil-rights matters and environmental and urban questions, the Reagan people appear to be moving somewhat away from those old absolutist ideas about heaving out the government altogether and letting Charles Darwin handle the rest.

This is good. It also is hard, maybe impossible. Can the U.S. government, acting as a kind of symbol of, and surrogate for, the society as a whole, concoct sensible, humane and relatively efficient answers to at least a respectable proportion of the problems we face? Will the Reagan government have the guts to move into that truly difficult area where you do neither everything nor nothing--but something that has risks proportionate to the prospective gain? While everyone is waiting for the economic plan's impact to be felt one way or, God help us, the other, there will be plenty of other case studies to observe in the administration's evolution toward a style and philosophy of governing. Civil-rights legislation, most particularly renewal of the Voting Rights Act, is one case. The really hot case of the moment, however, is that of the good old MX missile and basing system.

The full-fledged, 200-missile/4,600-shelter, now-you-see-it- now-you-don't, moving-van MX system has always struck me as almost a parody of the overdone, oversize government contrivance that purports to be a solution--and which everyone knows, somehow, just isn't going to happen and won't work if it does. If the Pentagon had n't thought it up, Mel Brooks would have. To his credit, Reagan and his aides seem to have begun trimming it down, not just for money reasons, but for program reasons as well. I think in fact that the way the president disposes of the broad array of military questions now before him will provide plenty of clues as to whether he can really do something about that huge and semi-senseless government reaction- machine he has complained of. For inspiration and guidance he should, whenever possible, contemplate the lowly fruit fly.