The assassination of a senior United States military adviser in San Salvador has furthered heightened the uncertainty in Washington over what the US role should be in Central America.
Several congressmen have asked for a US investigation of Lt. Cmdr. Albert Schaufelberger's killing by an unknown assailant. Those who oppose all further US military involvement in Central America are likely to point to this incident as another reason for ending military aid.
Yet early Washington reaction to the incident has been relatively low key.
While the Reagan administration's policies in Central America have some ardent congressional critics, Congress as a whole appears reluctant to totally scuttle programs like those of the advisers in El Salvador. House Speaker Thomas O'Neill cautions fellow Democrats not to ''go full force'' in criticizing the Reagan policy in the wake of the slaying of Commander Schaufelberger.
Although there are no more than 55 of them (the number is sometimes lower because of rotation), the advisers are deeply involved in virtually all military matters in El Salvador. They train Salvadorean troops. They advise Salvadorean military commanders on strategy and tactics. They attend high-level military staff briefings. And they fan out through the countryside to Army bases and units close to the fighting with leftist guerrillas.
''The Salvadorean military hardly buys a paper clip without approval by United States military advisers.'' That comment by a senior Salvadorean military official is at least part hyperbole, but it is clear that US military advisers in El Salvador do play a significant role in beefing up the Salvadorean Army's fighting potential.
While the advisers are under orders not to engage in combat, their mission is often dangerous, and this has frequently been alluded to by critics of the program. Helicopters in which the advisers ride are frequently fired upon. At least one adviser has been wounded. Others have been pinned down under ''unfriendly fire.'' The hazardous mission of the advisers was emphasized again this week with the slaying of Commander Schaufelberger. The US quickly issued orders to its other advisers on the scene to be particularly circumspect in their movements and contacts.
The advisers are some of the best military men the US has to offer - many of them schooled in counterinsurgency. Their commander is Col. John Waghelstein, himself a counterinsurgency specialist, who has handpicked many of the advisers.
One of their key goals is that of transforming the Salvadorean Army from a garrison-bound force of ''weekday warriors'' into mobile units capable of ''taking control of the night,'' as one US adviser phrases it. But the advisers report a great deal of ''institutional inertia.''
Yet they have doggedly continued efforts to remodel and modernize the Salvadorean Army - setting up, for example, six agile ''hunter batalions'' of 350 men each who are not afraid of countryside combat or night fighting. US advisers stay with these troops except when they actually saturate a small countryside region in search of guerrillas.
In addition, the US advisers are working with the new immediate-reaction Arce Batalion of 1,150 men, which is designed to quickly go after the guerrillas whenever and wherever they strike.
The US also has a broad plan that attacks the traditional way in El Salvador promotes its officers. The US is promoting a rapid promotion plan that elevates many junior officers who did not attend the Salvadorean Military Academy and who would not in the normal run of things expect to rise far in the officer corps.