WITH PRESIDENT Reagan urging that we send more military aid and advisers to El Salvador, it is worth recalling that Americans have been training Salvadoran military and police forces for more than three decades -- and without notable success.

In the late 1940s, American officers were in charge of the Salvadoran Military Academy. In 1948, we sent our first military mission to train the Salvadoran Air Force and to help raise its level of professional conduct. In the next 15 years our military missions grew so large that, by 1963, we had more men in our air mission than there were either pilots or planes in the Salvadoran air force. I was then our ambassador in El Salvador, and I formally requested that our large and conspicuous Army and Air Force missions be reduced in strength. My request was in vain.

At the same time we had police-training officers in our AID mission, and Salvadorans attended the police training school that we ran in the Canal Zone.

Although our officers could sometimes exert a beneficient democratic influence on the politics-minded Salvadoran officers, the American military was often unprepared for what it encountered there.

In 1948, the commandant of the Escuela Militar (the military academy which produced the officer corps of the Salvadoran Army) was a distinguished American colonel who had a gallant record on the beaches of Normandy and in the invasion of Europe. He was a fine representative of the U.S. Army, but there was some question as to whether his qualities were those most suited to the needs of the Salvadoran armed forces.

During a military coup d',etat on an afternoon in December 1948, this colonel came to our embassy, where I was then charg,e d'affaires. He said he was annoyed by the disappearance of his deputy commandant, a Salvadoran officer, whom he had instructed that morning to perform some administrative chores (using a contingent of cadets to spread manure on the parade ground). The deputy, one Col. Cordoba, had ignored the orders and dashed away in a jeep.

I can still hear the voice of our well-informed military attach,e, another distinguished officer, telling the commandant -- who had found us on the roof of our embassy -- to look at a puff of smoke in the distance.

"See the smoke over there? That's Cordoba. He just took over the government."

(Soon afterward another officer displaced Col. Cordoba as the new provisional leader.)

A dozen years later, in January, 1961, during another coup d',etat, many Salvadorans believed that the U.S. military mission had plotted and managed the overthrow of the reformist junta then in power. Local newspapers printed as evidence photographs of the chief of the U.S. mission at the military headquarters of the perpetrators during the coup. It mattered not that this American had simply driven to the central barracks trying to find out what was happening. Salvadorans saw photographs of the American officer mingling with those who, as Secretary of State Shultz would put it, had just shot their way into pwoer. Sincere advocates of reform were convinced that the American military had thwarted them.

While I was the U.S. ambassador to El Salvador in 1964, a small contingent of Green Berets, some of whom I understood had been among the early advisers in Vietnam, came to El Salvador to supplement the training already in progress under the direction of our military mission. The Green Berets may have made the Salvadoran soldiers somewhat better prepared for later duties -- especially in the Soccer War in 1969, the republic's most notable international conflict in this century.

That was the brief but bloody episode in which El Salvador's American-trained army fought the American-trained army of Honduras. History offers few such pathetic uses of U.S. military training as the war between those two U.S. proteges in the jungles and mountains on the border between the two countries. Only since 1979 has our military training in El Salvador attracted wide attention in the United States, even though it has been such a long and continuous process.

Before the coup d'etat of October 1979, we had already trained 2000 Salvadoran officers and men. We had provided more than $16 million in military aid -- not a large amount in today's dollars, but significant in the 1940s and 1950s and in relation to the 3,000-man army that El Salvador had when we first turned our attention to it.

Since 1979, the number of Salvadoran soldiers trained by us has doubled or trebled. The amount of military aid since October 1979, measured in the hundreds of millions of dollars, has put El Salvador among the leading recipients of U.S. military assistance.

In such volume and value, our aid has exceeded even the most exaggerated reports of any Soviet military aid that may have reached Salvadoran insurgents via Nicaragua or Cuba. It thus becomes legitimate to ask: Why has an insurgent army of 6,000 muchachos done so well against the 20,000-man army that we support?

Recently, nongovernment American military analysts have written much about the morale of the Salvadoran armed forces. They lead us to ask whether a young man seized in his village by a press gang and marched off to the barracks, with thumbs tied behind his back, to be put into uniform, can be as good a soldier as his adversary. In contrast, the insurgent muchacho is more likely to be a young man -- or woman -- who has joined the revolt out of a commitment to end social injustice.

No amount of presidential rhetoric can conceal the facts about El Salvador. No official U.S. rhetoric can persuade the poor of El Salvador that the regime we support has been improving their lot. If it had been, we would not see the increasing flow of refugees still fleeing the country for haven in the United States.

We need a better answer than the old panacea -- a better answer than merely turning up the volume of the military aid which, after millions of dollars and hundreds of man-years of training, has not been notably effective in 35 years.