The Post's editorial on Guatemala {" 'Dirty War' Again," Nov. 12}, while insightful in describing the horrendous human rights situation and lack of civilian authority despite five years of civilian government there, comes to a less than convincing conclusion.

The Post argues that despite military savagery, "keeping a hand in" Guatemala by continuing to provide military aid "can be useful." I have not yet seen, nor does The Post's editorial offer, an example of this usefulness.

The Post is right in noting that the Guatemalan army killed thousands after the United States ended military aid in 1977. But those developments were not cause and effect. In fact, our military assistance program ended because Guatemala's generals refused to accept any human rights conditions on aid. The choice presented to U.S. officials by the Guatemalan military was this: Keep giving us bullets, and keep your mouth shut about what we do with them, or take your aid and stuff it. How could continuation of U.S. aid under those circumstances have in any way been useful to human rights?

The circumstances in Guatemala today are not quite as bleak, thanks in part to the Carter administration and other governments' cuts in aid back in 1977. Tired of being treated as an international outcast and eager to court foreign donations, Guatemala's army allowed elections for civilian government in 1985 and again two weeks ago. It thus demonstrated its interest in moderating its practices to appease foreign governments.

Of course U.S. influence is limited in Guatemala, but the millions of dollars of U.S. military and security assistance being provided are clearly not moderating abuses. Instead they are bolstering a military engaged in unspeakable crimes. Guatemala's generals can hardly be blamed for reading that message as a blank check.

ANNE MANUEL Associate Director, Americas Watch Washington