The insistent whir of a Guatemalan Army helicopter broke the silence of the hot afternoon. The helicopter circled just short of the Mexican border, then swooped down and fired into the trees below.

"Guatemalan families came running out of nowhere, screaming," recalled Carlos Gomez, a Mexican farmhand who witnessed the scene. "There was terrible panic. When they got to our side, some of the people gave away their children to the Mexicans."

No one was hurt that afternoon of Jan. 14, but by the time the chopper rumbled off, nearly 300 men, women and children had sought refuge in Mexico. They said they had traveled on foot much of the night, fleeing from an Army raid that they said had left 18 dead in the village of Santa Cataria and 16 dead in the village of El Limonar. The chopper's crew had spotted their group as they approached the border and, apparently under the impression that they were guerrillas or sympathizers, had opened fire.

The group was another trickle in the flood of about 2,000 refugees each week that is pouring into Mexico as the Guatemalan Army wages the fiercest antiguerrilla campaign in its history. Over the past six months, the Army has stepped up its hunt for a tough, often invisible guerrilla force, and the refugees say it has inflicted a scorched-earth policy on Guatemala's western highlands. As a result, entire villages and hamlets have fled, often into Mexico.

In this rugged, unpatrolled land, there are few documented statistics. The State Department in its latest annual report on international human rights estimated that nearly 100 peasants a month were killed in Guatemala's escalating guerrilla war. It estimated that an additional 250 to 300 persons were murdered each month for what appeared to be political reasons.

"Increasingly, noncombatants are the principal victims of the violence from both sides," the report said.

A Western diplomat in Guatemala recently put last year's death toll at 5,000, most of them civilians, while the newly formed Guatemalan Unity Committee, an opposition group, put the figure at 13,500.

In interviews last month with Washington Post correspondent Christopher Dickey, Guatemalan military officers in the field readily conceded that civilians caught between them and the guerrillas were considered expendable.

"These people [the guerrillas] are difficult to distinguish from most of the rest of the local population," Gen. Benedicto Lucas Garcia, chief of staff of Guatemala's armed forces, told Dickey. " . . . Because of that, well, the population suffers."

The guerrillas have stated publicly that they at times also have killed civilians suspected of being government informants.

Guatemala's ambassador to Mexico, Jorge Palmieri, conceded in a recent interview that "there are military actions, and people who have nothing to do with it are afraid to be caught up in it, so they travel." He contended that there is evidence that the guerrillas "have manipulated people and led them to Mexico to cause upheavals."

Whatever the reason, there is no dispute that the refugees are coming here in record numbers. The Mexican Interior Ministry estimates that there are 120,000 Guatemalan refugees in this country now, more than double the figure of a year ago.

The winding, 565-mile-long dividing line between North and Central America has always been porous. Marked only by an occasional border post, like here at Ciudad Cuauhtemoc, it climbs across the peaks of the Sierra Madre, becomes the Usumacinta River, then loses itself in the dense tropical jungle farther north.

For as long as anyone remembers, merchants and migrant workers have crossed the border freely. But never has the flow been so large. Thousands of terrified, impoverished and often illiterate Indians have come to see the distance between their old homes and the Mexican border--often only a few hundred yards--as the difference between life and death.

Although it is quiet on the Mexican side of the mountains, the war has deeply strained the modest resources of the string of border towns where refugees have arrived. It has also unsettled officials of the Mexican government, who disclosed earlier this week that Mexico has authorized the training of a 4,000-man quick-reaction military force in part to cope with any possible spillover of the conflict.

Mexico has refused to allow the formation of refugee camps near the frontier for fear that the camps would quickly turn into armed guerrilla bases and worsen the country's already poor relations with Guatemala. Instead, the refugees are scattered all over southern Mexico, working in cities or on farms or relying on the good will of religious charity groups.

Pressure has been building on the government from conservatives who argue that Mexico already has enough social problems of its own and should put a stop to the new flood of penniless foreigners.

But when the government ordered the deportation of 1,800 Guatemalans last summer, it drew sharp criticism from the left as well as from Guy Prim, then the representative of the Office of the United Nations High Commissioner for Refugees, who said there was strong evidence that some deportees were being murdered on their return to Guatemala.

Most of the refugees, like much of Guatemala's highland Indian peasantry, seem conservative, devout and xenophobic. The stories they tell in broken Spanish of half-empty or deserted villages, burned homes and dismembered bodies present a picture far removed from the tight social order that for centuries has ruled one of the oldest cultures in the Americas.

Their accounts offer glimpses of a bitter, often bloody conflict that has gone largely unreported to the outside world. Few outsiders travel to the remote villages in the provinces of Huehuetenango, Quiche and San Marcos, where most of the fighting has occurred, and suspicious locals seldom confide in those who do.

The Guatemalan government insists that the guerrillas bear much of the responsibility for any atrocities that have occurred. Earlier this week, the Army blamed guerrillas for the massacre of 53 Quiche Indians in the village of Chumac.

But in a week of interviews, more than two dozen refugees offered repeated accounts of brutality by the Army and none by the guerrillas.

Near Motozintla, a village tucked against a barren mountainside, Jacinto Pascual, 60, explained why he, his wife, their children and grandchildren had abandoned their home in the Guatemalan village of Tacana last December. He said the pintos, a Guatemalan pejorative for soldiers, had killed 40 villagers in Tacana, including "whole families."

Pascual, whose possessions were reduced to what he could carry across the border in a plastic shopping bag, apologized for crying "right here in front of my wife. I'm not afraid of death. I've lived my time. But I'm afraid of the way the pintos kill. They first cut off the ears, then the nose, with a machete. They cut out the eyes and the tongue. I heard them say they don't want to waste their bullets."

On the flight to Mexico, he said, his family had found four bodies in a forest. "Two had their hands and feet cut off," he recalled. "Two had no more tongue."

Women express the same fears: being raped by the soldiers and being burned alive in their huts. Religious workers said that many frontier families tend their land and animals in Guatemala in the daytime and sleep in Mexico at night.

One widow who lives in Guatemala, but sleeps in Mexico, said she could no longer sleep when at home: "I've seen the fires at night. The soldiers bar the doors [of the huts], throw gasoline and burn everyone inside."

Candido, a wounded Catholic lay preacher from Neton, said he had been dumped from an Army truck a few days earlier after faking death. Soldiers had tied his brother behind the truck, "pulling him at great speed until he died," he said. Efrain Moreno, a former government employe just arrived from Neton, said the village had been completely abandoned.

A Mexican nurse, who said she has extracted "many a bullet" from the refugees, angrily recalled an incident two months ago when a woman from Neton brought her badly burned 9-month-old granddaughter for treatment.

Government soldiers had come to the woman's house seeking her son. When she told them she did not know his whereabouts, she said, they held the baby's feet over burning coals in the fireplace.

"Its feet were burned to the bone," said the nurse. "I saw it with my own eyes." The nurse, who asked not to be identified because she feared that Mexican authorities disapproved of her work with the refugees, said the baby survived and subsequently was taken to a hospital for a series of skin grafts.

Sometimes the impact on Mexicans of the Guatemalan conflict is a subtle one. In the Mexican village of Niquivil, built in a high pass often covered in clouds, the villagers do not go out at night. The mountains are haunted, they say, by the souls of the scattered, unburied dead across the border.

For the past six months, peasants have pulled bodies out of the Cuilco and Selegua rivers that run from Guatemala into Mexico. "The people here have been very shocked," said a local priest. "Many of them will not eat fish from the rivers anymore."