When science fiction writers tell stories of military conflict set in the far future, they are saying that, in their world view, the elements in our characters that create war are so deeply rooted that we will still have been unable to eliminate them thousands of years from now. The first two volumes of Orson Scott Card's Ender trilogy, Ender's Game and Speaker for the Dead (Tor, $13.95 and $15.95), are rife with this dyspeptic view of the human race, but Card is a writer of compassion and his heart breaks for the individual men and women of good will who find themselves caught up and forced to participate in the race's homocidal crossfire.

Ender's Game is the story of a 6-year-old computer genius whose childhood is ripped violently from him when the military, seeking to exploit his talents in a war against an alien race, drafts him into a savage "battle school" where children make war on children. Here Card focuses on the question: What happens to the heart and soul of those, unremittingly trained for war but essentially innocents, who for the (possibly delusional) safety of their people commit what amounts to genocide? Can a person redeem himself, especially in his own eyes, after helping to wipe out every man, woman and child of another people? Speaker for the Dead, set 20 years later, offers Ender -- who had been tricked into xenocide in the first book by being told the battle he waged was a computer simulated practice run -- a chance to redeem himself.

Once again humanity is on the verge of committing xenocide, this time against a highly intelligent but socially primitive culture whose genetic structure threatens Homo Sapiens with a devastating viral plague and, although biologists have already learned to contain it, frightened humanity as usual would rather shoot first and ask questions later. The climaxes of both volumes invoke quasi-religious images and themes, (what else can we be expected to make of an alien race whose members are, quite literally, born again but who must first undergo actual death, through a process curiously resembling crucifixion), which suggest either some unresolved inner conflict on the author's part or else the subject matter to be dealt with in the concluding book of the trilogy. Bravos

If Orson Scott Card examines the moral cost of military conflict, C.J. Cherryh -- whose extraordinary gifts are not as well-known outside the science fiction community as they should be -- focuses on the human costs of military conflict, not only in terms of death and suffering, but also the destruction it wreaks on the lives of those who survive. As we learned once at Lexington and Concord and again to our cost in Vietnam, decisive military conflict need not necessarily involve armies throwing massed might at one other; it can also involve highly- disciplined guerilla bands or paramilitary groups.

In Angel with a Sword (DAW, $15.95) private militias are struggling for control of an off-world planetary Venice of canals, boatmen, minarets and slums. Cherryh's protagonist, a young canal woman from the city's watery slums, precipitates herself into the middle of this conflict, when she rescues a high-ranking member of one of the feuding militias from drowning -- in a city where any contact with anybody, for whatever reason, is regarded as a political act in support of or endorsing someone's friend or enemy . . . and all enemies are to be shot on sight. Cherryh takes advantage of the fact that her two main characters come from opposite sides of the canal to demonstrate how the ravages of war cut across, and bite into, all levels and stratas of a society and to show how each reacts to preserve what it sees as its own self-interest and/or position, quite often to the detriment of the whole. Alien Economics

Whatever his personal antecedents, the late L. Ron Hubbard obviously had a strong personal antipathy to bureaucracy, particularly the military and espionage establishments with their callous manipulation of and disregard for people, things and events. Unlike Card and Cherryh, Hubbard has chosen to make fun of his target rather than dissect it. In The Invader's Plan (Bridge Publications, $18.95), the first volume of a proposed dekalogy (ten volumes), Hubbard spins a satirical tale in which our world has been marked for potential exploitation by a more advanced, and equally ruthless, race. The jape: One of their advance scouts discovers that, between the threats of global pollution and nuclear warfare, we are in danger of destroying the earth before they can exploit it and wiping out a considerable investment in money, time and research as well -- so to enslave us, they first have to save us (from ourseles).

Almost all of The Invader's Plan is a delicious read and, as one would expect of an experienced pro, Hubbard makes his points well; the major question is whether the book's flippant, light-hearted tone can sustain itself over some 5,000 pages. On the other hand, Hubbard is no stranger to the form. Much of his best work of the '40s and '50s, Fear, Slaves of Sleep, Typewriter in the Sky, is written in exactly the same style and won reader polls at the time. Growing Pains

The uses which first-novelist Bill Baldwin makes of his story's military background are not so ambitious as those of Card, Cherryh and Hubbard. Instead, Baldwin is telling the kind of stirring old-fashioned space opera which, in the hands of genre founding fathers Edmond Hamilton, E.E. Smith and Jack Williamson, set hoards of adolescent minds afire. In fact, Baldwin's book, along with much of this sub- genre and several others within the field, might more correctly be labeled "Young Adult." We do not expect extreme moral complexities in a young adult novel and Helmsman (Popular Library, $2.95) does not attempt to give them to us: Instead, it recapitulates the by now traditional, and perhaps almost obligatory first novel of choice: that of a young intellectual outsider/misfit, Wilf Brim, a military cadet from a backwoods planet who rises, in spite of social disfavor and the wrong-headedness of his superior officers, to save the fleet, the day and his people.

As with all fabulations created specifically for the young, whether people or cultures, everything in Helmsman is couched in terms of black and white: higher-ranking officers who oppose Wilf are either fools and blunderers or spiteful individuals whose enmity he has incurred from being right when they were wrong or because of their prejudice against his origins. War is portrayed as an archetypal struggle between good and evil in which a peace-loving people must rise up to end oppession by forcibly dissuading the perpetrators from their evil ways, in the classic vein of "might for right." Those who respond to this kind of fiction will find Baldwin rewards his readers with fast action, well-thought-out plotting and some delightful characters, especially Barbousse, a gangling dissembler who rescues Wilf on a number of occasions in the time-honored manner of eccentric, engaging sidekicks everywhere (and when).

Good writers employ war's exigencies, epiphanies and dramatic contrasts to raise serious moral issues or to illuminate contradictions in their own culture's positions; lesser writers may even, without debasement, employ them in the service of a suspenseful plot or to reinforce socially approved behaviors and codes. The problem arises when war is simply glorified. The distinction may be a subtle one -- for even the best of writers may waver -- and it lies not in whether a writer is for or against war, but in how he presents it, in how honestly he portrays war's terrible toll in life and limb, its psychological carnage, its economic and social devastations; or in whether he chooses, for whatever reason, to subordinate these to mere background details, while appealing to the feelings of power and conquest war can bring. In our own culture, nearly the only place such issues are being debated fictionally are in the handful of Vietnam novels, and in science fiction.