MILITARY INCOMPETENCE; Why the American Military Doesn't Win. By Richard A. Gabriel. Hill and Wang. 208 pp. $16.95. Betts

IT IS NATURAL in a free society that trends generate their own opposition. After great success in increasing the defense budget, the Reagan administration is on the defensive against critics, who see it as unsustainable in the face of fiscal crisis. Other critics, however, quite happy with the aim of overweening American power, deride our military's capacity to exploit its surfeit of resources in the situaion that counts: combat. Richard Gabriel's polemic is in this genre.

There's good news and bad news about this book, and even the good news is bad. What's good is Gabriel's disturbing chronicle of consistent foul-ups in the planning and execution of U.S. military operations since 70. As muckraking it is done well, though the author's military-bashing is a bit too zealous. For example, he argues that poor performance was too extensive to blame on directions of civilian leaders, as military men are wont to do. But the fact remains that in most of the cases political imperatives were crucial in forcing the military to undertake high-risk actions under close to impossible conditions (the Mayaguez incident, raids to resue prisoners at Son Tay and the embassy in Tehran, and the dispatch of Marines to Beirut). And a fair number of glitches in action are the sort typical for any military force in the fog of war. Particularly in Grenada some problems -- though not the major ones -- might be blamed on the short time available for arranging the attack.

Some mistakes are also evident only with the luxury of hindsight. A major problem in the Iran rescue attempt was excessive compartmentalization of planning, to preserve secrecy. Secrecy, however, was one vital element in the operation that did not fail, despite the porousness of our government which makes leakage of sensitive plans the norm rather than the exception. If the plan had been better coordinated, but surfaced before it could be executed, would the post mortem verdict be the same?

Although mitigating considerations make failure a bit less egregious than the author suggests, the record is too bleak to discount. Gabriel's argument is not new -- it repeats familiar charges by Edward Luttwak, William Lind and Jeffrey Record -- but this book lays out the gloom in depressing detail.

The bad news is that good description of symptoms is matched with questionable diagnosis and poor prescription. Gabriel's case studies do not bear out his principal thesis about the cause of the problem, and his final recommendations contradict what the cases do point to as a root of the problem. The author attributes military ills to the size of the officer corps, which should be cut drastically, and argues for relying on combat leaders rather than managers. Yet he says contradictorily that the corps is simultaneously bloated and overburdened, and later endorses returning to conscription because it would expand ROTC programs. The officer surplus is not clearly linked to operational mishaps in his combat cases; indeed, he faults the Iran rescue team for not including a larger staff element.

Gabriel also recommends shrinking the officer corps by slowing promotion and requiring longer service before retirement. But might slower promotion weed out officers whose ambition reflects talent? Modifying excessive turnover is a good idea, but if carried too far could replace an unstable personnel system with a sclerotic one.

THE PERNICIOUS FACTOR that does emerge consistently in the cases is interservice competition, which damaged operations by allowing too many cooks into the kitchen. Yet the author's final recommendation is to fire the chef in charge -- to abolish the Joint Chiefs of Staff and replace that weak coordinating institution with strong general staffs for all four services -- an anarchic decentralization that would let the cooks run free and aggravate the rivalry he reviles. Gabriel himself at one point recalls the crazy situation in the Spanish-American War -- before the JCS was created -- when the Army and Navy stonewalled each other in a dispute on how to take Santiago. And he faults the Iran mission for insufficient unity of command. The JCS should not be junked but reformed and strengthened, to discipline service parochialism.

The book's prose is gratifyingly readable, but facile writing (this is the author's 15th book) takes its toll. There are a dozen trivial errors and careless lapses of logic. Most of the case studies are based on very few sources, and some shocking accusations cite no source, or are not mentioned in the source footnoted (for example, he charges that planes cannibalized for spare parts ''are often counted as combat-ready," but this is not stated in the source).

Sloppiness unfortunately provides skeptics an excuse to dismiss the indictment more easily than they should. I was predisposed to be more tolerant of military mistakes until I waded through Gabriel's five case studies. I still believe his hope of debureaucratizing the military is oblivious to the difference between what is possible in a complex institution which has more difficult global responsibilities and less constantly pressing challenges to survival than does a model like the Israeli army. Though this book doesn't quite fill its own bill, there's enough in it to warrant anxiety all along the political spectrum from left to right.