Antonio Martinez is 38 but looks 50, slumped against the corrugated cardboard wall of the refugee center he now calls home. The guerrillas came well before dawn, he says, shot three of his sons and ordered him to leave town with nothing but what he wore.

On that night in October 1980, nearly 50 families fled the little collection of houses in the hills six miles north of this rural town, stumbling down a dry riverbed in the dark to get here. And here most of them remain, either afraid to return or, like Martinez, empty of hope.

"They took the chickens, the goat, the ducks, everything. There's nothing left to go back to," he said. His eyes have the vacant look of those whose lives can hold no more surprises.

In three church-run centers near the provincial capital of San Vicente there are about 1,500 refugees who say that left-wing guerrilla terrorism has ruined their lives. With the earnest, weathered faces of the rural poor, they are just as believable as the thousands of refugees in other camps who say they fled the advancing Salvadoran armed forces or right-wing terrorists.

In San Vicente, Concepcion Amaya de Carrillo was patient as she waited in line for powdered milk and beans at the food-supply center run by Caritas, the local charity arm of the Roman Catholic Church. She said she had lived as the wife of a tenant farmer in the village of El Rodeo near San Isidro, 15 miles northeast of San Vicente, until a night last October.

"The guerrilla terrorists banged on my door at 3 a.m.," she recalled. "They said we could either join them or get out, or we would die in 24 hours." She and her husband and three children fled with what they could carry. How did she know the invaders were guerrillas? "We know. They had big guns. They did not wear masks, and their accent was pure San Isidro," she said.

Leftists here argue that such incidents are often the work of military men disguised as guerrillas. "The final victory depends on the good will of the people. Why should 'the guerrillas' alienate them that way?" asked one.

The government says many murders blamed on right-wing or military terrorists are actually committed by guerrillas settling internal disputes. Both sides agree that common criminals take advantage of the general violence to commit other crimes, and both sides say frankly that they shoot spies and known collaborators with the opposition.

The charges from either side often are impossible to verify. The Army often works with militia who carry M1 and G3 rifles while dressed as civilians, and the guerrillas often wear stolen military uniforms.

In the town of Yamabal, near San Miguel in eastern El Salvador, three men dressed as regular Army soldiers arrived last Monday saying they were the first of a company coming to protect the village and wanted to review the Civil Guard. When the men were lined up, the three opened fire, killing 11 men and wounding five more. The killers escaped in the confusion, and newspapers reported that scores of people fled Yamabal for San Miguel.

The civil war in this small country seems always to burst forth that way, sporadically and unpredictably, like a political version of the molten unrest beneath the volcanoes that dot the landscape. Every guerrilla push and every military operation seem to create more refugees, leaving the houses to molder and the crops to rot.

Estimates of the displaced now range upward from 500,000, or 10 percent of the population, with two-thirds of them out of the country. It is as though the population of California were suddenly homeless, penniless and frightened, spread out across the United States.

In this part of El Salvador, a 90-minute bus ride northeast of the capital, the Army has just completed a four-day sweep against suspected guerrilla camps. "Some of the refugees from that action are now coming in," said David de Jesus Bonilla, director for 15 years of San Vicente's branch of Caritas.

Bonilla showed with little pride the eight open-ended sheds the church has put up to house more than 700 refugees. The sheds have walls of latticed bamboo, faced with clay by the refugees, who live two families to a dirt-floored room, about 15 feet square. Juana Gabriela Portillo, 50, and toothless, has two narrow beds for her family of nine, and four of them sleep on the ground.

They left the village of La Esperanza, near Tecoluca, last August when the guerrillas came through, and even though the Army has declared the region clear of rebels, "we can't go back there," she said. "They took our clothes, the pots and pans even, and they told us never to come back. I was very scared."

When the guerrillas first rose against El Salvador's rulers in the early 1970s, "they weren't violent. If the people didn't want to join them, they were very polite," recalled the Rev. Rene Valle, priest of San Esteban Catarina. "But many resisted and many were 'ears'--government spies--and finally the boys began to shoot also."

Valle came here in August 1979 when his predecessor, the Rev. Napoleon Macias, was gunned down as he turned from the altar after mass. "Yes, he had gotten involved in politics. We still aren't sure which side killed him...no, there was no investigation. There never is," said Valle.

After that shooting, many residents left here for San Salvador, fleeing the right-wing terrorists they blamed for it, he continued. Their homes were occupied by refugees from rural areas who were fleeing the guerrillas.

In the huge, filthy courtyard of what once was a large and probably elegant home, a tin roof shelters a labyrinth of 30 or so dark, tiny rooms partitioned from each other by sheets of cardboard. Smoky cooking fires burn on makeshift clay stoves and naked toddlers sit dully in the corners. "Come in, come in, sit down," says a woman. "See how nice it is now that we have the walls."

Dr. Carlos Roberto Navarrete works long hours at Caritas' clinic in San Vicente, treating worms, skin troubles, dysentery, tuberculosis and other diseases of the poor. He has worked here six years, and he said the number of people who are brought in with severe mental problems has increased 25 percent during the last two years.

"There is so much fear, and when they lose everything it's hard to cope," Dr. Navarrete said. The walking wounded are easy to spot, wandering through every town laughing at nothing, arguing with ghosts and living on handouts from people not quite as badly off as they. The hopeless cases rarely come to doctors, he added.

In front of the cardboard wall where Antonio Martinez sits gazing at nothing much, there is a small cement slab with an ornate little cross, draped with plastic flowers. Under the slab lies the body of a neighbor's son. "We carried him out the night we left," murmured Martinez. "He was a good boy."