Why El Salvador's Army grows more confident

The Salvadoran Army is suddenly flushed with a string of small, but spectacular victories over leftist guerrillas.

Together with the massive outpouring of voters in last Sunday's balloting - which is viewed as a repudiation of leftist violence - the Army wins have considerably boosted the morale of the hard-pressed foot soldiers.

It has also put the guerrillas on the defensive.

Moreover, when the battalion now being trained at Fort Bragg in the United States returns to El Salvador in early May, the Army's effectiveness will receive an additional boost.

In the past several weeks, and particularly during election week, Army units around major cities and key installations ambushed scores of guerrillas - killing and capturing an estimated 400, according to the Army's preliminary reports.

Behind this new success is a major change in the Army's fighting tactics. The Army has decided to fight like guerrillas. Instead of trying to attack rebels with massive strikes, the Army now is sending out small units of a half-dozen-or-so men to locate guerrillas.

The result is a rapid improvement on its battle score card. The Army has less of chance of losing its struggle than it did just six weeks ago. In 1980 and even early 1981 the Army suffered major losses to leftist guerrillas.

The Army has ''taken the night away from the guerrillas,'' comments an informed source close to the Salvadoran military. Most of the encounters have taken place at night or in the early dawn.

It hasn't been easy for the Salvadoran Army to turn conventional tactics around. The battle-seasoned, US-trained Atlacatl Briage (battalion) has led the way with the new tactics. Other units are following.

Still, the US trainers have had limited effectiveness preparing battalions for new tactics here. So the Salvadoran Army may get more training in the US.

Meanwhile, the Army's new tactics have demonstrated to top Army officials that their earlier battlefield approaches were simply inadequate for a guerrilla war of the magnitude now under way here.

A key factor in the changing tactics has been the flow of information on guerrilla activities given local Army commanders in the countryside.

This is a new development. It fits clearly into the political picture emerging from last Sunday's massive outpouring of voters. Perhaps as many as 1.2 million Salvadorans gave the message that they want an end to the violence.

But no informed observers really expect an early end to the violence. There is widespread speculation that the guerrillas may now lie low to assess both the Army victories and the election results.

There is also speculation that the new tactics are leading the guerrillas to reassess their own battle techniques. Guerrillas appear to be increasingly well armed and to control sizable pockets of this Massachusetts-size country.

An Army source here says, perhaps optimistically, ''We'll be ready for them, whatever they try.''

But the Army has suffered numerous casualties in latest battles, too. Company commanders are making it clear to their men that casualties accompany wins.

That warning aside, the mood in the Salvadoran Army is obviously upbeat at the moment.