IT IS A little bizarre: the military leadership on both sides of the war in El Salvador is changing at precisely the same time. In the government, the high command has named itself a new minister of defense. As for the guerrillas, the Nicaraguans report that the No. 2 in what is commonly believed to be the most radical faction was murdered by an associate, and the No. 1 committed suicide when he found out.

The outgoing minister of defense, Jos,e Guillermo Garcia, was the sole political survivor of the reformist junta that overthrew the oligarchy's military pets in 1979. He became the chief patron of what reform has since taken place, but, El Salvador being El Salvador, he could not effectively contain either the guerrillas on the left or the gorillas on the right. His fellow officers have now brought in Gen. Carlos Eugenio Vides Casanova. He has been commander of the National Guard, or rural police, where on his office wall hangs a teasing quotation from Abraham Lincoln: "You cannot strengthen the weak by weakening the strong." You can say that it is reassuring to find the key leader in a nation at civil war looking to Lincoln for some of his inspiration, though the exact meaning of this quotation in its Salvadoran context may not be so reassuring.

Salvador Cayetano Carpio, the longtime Marxist guerrilla commander reported to have taken his own life, can hardly be said to have fit the Lincoln mold himself. Whether he actually intended to strengthen the weak is a question. There is no doubt he wanted to weaken the strong. What is known of this veteran of the struggle is that he hated and distrusted the United States, felt close to Cuba and the "protracted popular war" faction in the Nicaraguan Sandinista leadership, and was among the most reluctant of the guerrilla personalities to countenance "dialogue" with other elements of Salvadoran society.

One does not want to invent possibilities that are not there. The basic fact of El Salvador, however, is the war and, by chance, circumstances are bringing new leaders, and therefore new possibilities, to both sides. It cannot fail to be a moment of a certain common pause and reflection. What the two new leaderships could see, if they could see very clearly, is that their struggle is destroying their country. Their foreign friends must see clearly, too.