SAN JOSE GUAYABAL, EL SALVADOR, FEB. 7 -- Two young men and a boy, whose tortured and mutilated bodies were found last week on the outskirts of the capital, were killed by a special forces unit of the Salvadoran Army, according to family members, villagers who saw them picked up, church officials and human rights workers.

The three bodies, dressed only in underpants and blindfolded with their thumbs tied behind their backs, were found Monday in a ravine called the Devil's Gate, a notorious dumping ground for victims of extreme right-wing death squads in the early 1980s. It is located in the mountains about seven miles outside of the capital, San Salvador.

The three victims had been badly beaten, cut and burned with cigarettes before being shot in the head.

The killings are the latest in a series of recent violent incidents in which elements of the military and security forces are believed to have been involved, raising fears among diplomats and human rights groups that El Salvador's human rights record is regressing after having improved in recent years.

According to diplomatic sources, the U.S. Embassy is investigating about 15 recent cases of major human rights abuses and has made its growing concern known to both the military and government. The U.S. is the biggest backer of the Salvadoran government, providing more than $100 million in military aid annually.

Human rights observers say the Army and security forces have improved their rights record dramatically since President Jose Napoleon Duarte took office in 1984, largely because of U.S. pressure.

Most say the current incidents, as opposed to those in the past, are not sanctioned by the upper levels of the military or the institution as a whole.

An estimated 40,000 people were killed by right-wing death squads in the early 1980s, and killings were often directly tied to the Army or security forces.

Military and diplomatic sources attribute the new rise in abuses to three factors: an end to the state of emergency under the Central American peace accord, a feeling by some that the war is not being won quickly enough and may drag on indefinitely unless tactics are changed, and increased political polarization.

"With the state of emergency gone, security forces have only 72 hours instead of eight days to hold a prisoner before turning them over to the courts," said one top military source. "They are growing impatient and take more extreme measures to get the person to break sooner."

Maria Julia Hernandez, head of the Roman Catholic Church's human rights office, said there has been a sharp increase in reported abuses since October.

Human rights workers say security forces have switched in recent years to the use of pychological measures including sleep deprivation, blindfolding prisoners and forcing them to stand for hours while being interrogated, and threatening the prisoner's family.

According to three sources who know the military well, some younger officers feel human rights requirements are slowing down the Army's ability to fight the war, now in its eighth year.

"Abuses are increasing because this is a dirty war and consequently calls for extraordinary measures," said one. "The enemy can use any tactics, and we are hogtied or hamstrung from defeating the enemy."

In a highly polarized nation, where reports of human rights abuses are distorted by both sides in the war, it is uncommon to find more than a dozen witnesses who agree on the essential elements of a story and will identify the suspected perpetrators, as in the current case.

"There is no doubt in my mind that it was soldiers of the {Army's} First Brigade," said Hernandez. "The place the bodies were dumped was obviously a warning, symbolic."

Col. Mauricio Ernesto Vargas, chief of the military operations department, did not rule out the possibility that soldiers did it, but if so, he said, it was an isolated incident, not a policy of the institution.

"This action is the product of sick minds who have no space in our society," Vargas said. "Anyone could have done it, and they would try to blame us. It will be investigated no matter what the consequences and punished."

U.S. Embassy spokesman Jake Gillespie said the United States was "deeply concerned" about all human rights abuses in El Salvador and would follow the case closely.

The three victims -- Luis Cornejo, 27; Manuel de Jesus Santamaria, 25; and Manuel's nephew, Javier Santamaria, 14 -- were from a hamlet near this town 15 miles north of the capital, at the base of the Guazapa Volcano.

It is an area where both the military and leftist guerrillas are active.

More than a dozen villagers, including family members and people who saw the men being taken away in a white pickup truck, all said special forces of the First Infantry Brigade grabbed the three men separately as they returned home from a party on the night of Jan. 31.

The soldiers were looking for the three by name, villagers said. The three were well-known in the village and were not known to have open political sympathies.

"It was the PRAL that did it," said Dinora Melgar de Cornejo, wife of Luis Cornejo, referring to special Long Range Patrol units of the Army's First Brigade.

She said her husband was killed because the PRAL had recently asked him to help gather intelligence information, promising him money. He refused, she said.

The Rev. Gregorio Rosa Chavez, auxiliary bishop of San Salvador, said in a televised mass today that the PRAL was responsible for the killings.

"We are returning to the period when 40 bodies would appear every day along the highways with the same characteristics as today," Rosa Chavez said.

According to the witnesses, who asked not to be identified for fear of retribution, four of the men in the pickup truck were in civilian dress and carrying M16 assault rifles, which are standard issue in the Army. Soldiers in uniform helped stand guard, the witnesses said. Five shells used in the M16 were found near the bodies.

According to the villagers, a man known as Tony provided information to the Army about the three that led to their detention. Tony was known because he had been a guerrilla who operated in the area before switching sides and informing for the Army.

There have been other examples in recent months of official brutality, including three separate incidents in which men died in police custody, reportedly after being severely beaten.

In November, a hotel clerk was picked up by the National Guard, injected numerous times with poison and left for dead.

The military high command met Thursday with the government human rights commission, promising to investigate the killings.

"They always promise investigations, and we keep dying," said one man here. "We know it was the military, but we know they will never be punished."

One West European diplomat who monitors human rights said the most disturbing thing about the triple killing was that more than 50 people showed up when the bodies were found, looking for missing relatives.

"To me this says there are a lot of people with missing relatives," he said. "It is an act of desperation to go looking for bodies."