Captain William of the Popular Liberation Forces had deployed two companies of guerrillas on the main road to Suchitoto, searching buses, bumming cigarettes and chatting with passers-by. A dozen Civil Defense troopers with makeshift uniforms and G3 automatic rifles stood guard at Tecomatepe, a village about 12 miles south of here, and a National Guard detachment in shiny leather spats was on hand in this largely deserted and amply scarred city 25 miles northeast of the capital.

In between, along the highway to what used to be one of El Salvador's tourist destinations, was guerrilla territory. The rebels, one of five groups in the Farabundo Marti National Liberation Front, have controlled passage sporadically for months. They were out in a force of more than 200 Sunday, marching up and down single file and stopping traffic at checkpoints under fat drops of a warm June rain.

The demonstration of rebel force had been going on for several days, like a clenched fist defying the authority of the U.S.-supported Army and the sovereignty of the government 40 minutes away in San Salvador. It was a clear lesson for motorists passing through and for peasants loading belongings on pickup trucks to flee what could turn into a battle zone where they would once again be caught defenseless in the middle.

Similar lessons have been given increasingly in broad swaths of Chalatenango province, just north of here, and in Morazan province, in El Salvador's eastern hills, since last fall. Outsiders can only guess what conclusions the country's close-mouthed peasants and villagers draw--whether they detest the guerrillas for disrupting their lives or despise the government for letting it happen, or both. But it seemed clear on the road to Suchitoto that they knew who was in charge of that little piece of the country for the time being.

It is to reverse the lesson that the government, at strong U.S. urging, launched an ambitious new operation in San Vicente province southeast of here. "Operation well-being for San Vicente," as it is called, includes a pledge that the Army will remain in force around the province and protect civilian attempts to restore the area to normal economic activity.

Col. Rinaldo Golcher, the commander, says he has more than 5,000 soldiers at his disposal, including some U.S.-trained "quick reaction" units to bolster regular troops assigned to this operation along with the provincial brigade ordinarily on hand. Guerrilla attacks elsewhere will not lead to reassignment of his men, Golcher said, because lack of staying power and followup have been diagnosed as the Salvadoran Army's main tactical problem.

This seemed particularly apparent as Captain William and his men stood around the other afternoon. Guerrilla attempts to capture Suchitoto in February--the most recent of many--had led to a strong Army counteroffensive that included bombing by U.S.-supplied A37 Dragonfly jets and resulted, after heavy fighting, in reestablishment of government control over the area.

Things had changed markedly since then. But Captain William had nevertheless taken his precautions. Lookouts were posted on a high rise with a view to the south, keeping in touch with walkie-talkies. A field radio, its batteries dripping white acid down a rebel's back, was never far from his reach. The forces boasted at least one rocket-propelled grenade launcher and a light machine gun to back up their M16 automatic rifles.

There seemed to be little fear on Sunday that the Army or Air Force would attack soon to challenge the rebels' open presence there. A few feet off the road, one guerrilla was dishing beef stew out of a black iron cauldron and his comrades were mixing it with corn meal, served on a tortilla in the absence of a plate.

(Government planes did bomb the area Monday night and Tuesday, witnesses said, but on Thursday, the rebels had moved along the road to dynamite Las Guaras Bridge, The Associated Press reported, isolating Suchitoto.)

The field radio operator and several other guerrillas were women or girls. One shy girl, who seemed no older than 16, wore no uniform and carried no weapon. Others were dressed in olive fatigues or blue jeans like their companions, however, and carried the U.S.-made M16s that, except for a few West German G3s, appeared to be standard issue.

Strangely, in a part of the world that gave machismo its name, none of the women seemed involved in preparing or serving the lunch. A pudgy young rebel, standing guard as his comrades searched passengers of the Suchitoto-San Martin bus, said the shakedown was designed to make sure no soldiers or Civil Defense troops were aboard.

The commander of the Civil Defense unit at Tecomatepe, with half a dozen men and boys at his disposal, said there was little he could do because the guerrillas numbered in the hundreds.

In the town's only indoor restaurant, a square-faced girl complained that she had nothing to serve because the guerrillas had cut off the road and nobody had brought anything in from San Salvador or the market at San Martin, on the Pan-American Highway 18 miles south. Reminded that traffic seemed to be passing through the guerrilla positions without trouble, she said: "Yes, but it is still very dangerous."