In an editorial {"An Eye on El Salvador," Aug. 24} The Post says that the FMLN guerrillas "came out pretty well" from their offensive last November, in part because "Congress, far from penalizing them for starting the offensive, instead halved aid to the government for a massacre -- the killing of the Jesuits -- that army officers perpetrated in the heat of battle."

This is an irresponsible way to describe that massacre. Killings "in the heat of battle" may involve combatants or those who happen to be in the path of a battle. The killings of the six Jesuit priests and of their housekeeper and her daughter were nothing of the sort. They were planned and carried out by army officers against people known not to be armed and when there was no battle in the immediate vicinity. They are more appropriately described as cold-blooded killings. The only relevance of the FMLN offensive is that the military officers who killed the Jesuits apparently took advantage of the offensive to do something they had probably wanted to do for a long time.

I suggest that congressional outrage over the killings reflected a more realistic assessment of what happened than the one proposed by The Post. ARYEH NEIER Executive Director Human Rights Watch Washington

The editorial "An Eye on El Salvador" was biased and one-sided. While no one likes to contemplate further violence in that tortured country, the government of El Salvador must share in much of the blame. Negotiations have stalled because the government has been unwilling to pay the price for peace.

A demand for sweeping changes in the armed forces is by no means ''outlandish,'' as the editorial calls it. The Salvadoran military has been implicated in the deaths of thousands of innocent civilians. Evidence linking high-ranking officers to the murders of the Jesuits has been concealed and withheld, although even President Alfredo Cristiani has admitted military involvement. The assassination of Archbishop Oscar Romero, the murder of the four North American church workers, the bombing of the Fenastras union headquarters and countless civilian deaths make up the bloody list of human rights violations allegedly linked to the armed forces. Why should it be unreasonable to demand the abolition of this murderous machine? Moreover, the elimination of the military is not without precedent in the region. Costa Rica has been without an army since 1948 and is now considered a model for peace.

It is time for our own government to send a clear message that continued atrocities in El Salvador will no longer be tolerated. The taxpayers of the United States have contributed $1.5 million a day to the brutal government of El Salvador. The proposal by Sen. Christopher Dodd (D-Conn.) and Sen. Patrick Leahy (D-Vt.) to cut military aid by 50 percent, contingent on successful negotiations, would be a good step in that direction.

A new offensive on the part of the FMLN would be unfortunate. It is the people of El Salvador who suffer the brunt of the endless violence. But to avoid continued bloodshed, both sides must demonstrate good will at the negotiating table, and Congress must create the incentive for the resolution of the conflict. It is time the government of El Salvador does its part to end the conflict by agreeing to true and profound reforms in its military.

BARBARA L. DOLE Silver Spring