LOLOTIQUE, EL SALVADOR, JAN. 6 -- Silvio Mendez has spoken, and now he is afraid. He drew a finger across his neck and said evenly, "They could cut my throat."

Mendez, who farms the craggy hillsides just north of here, is one of at least two Salvadorans who say they spoke with two American servicemen after their helicopter was shot down by leftist guerrillas here Wednesday -- and who saw them a few minutes later dead, shot through the head.

Mendez's account corroborates the statements of other farmers and a U.S. military forensic examination, which have led U.S. officials to the conclusion that the rebels shot the Americans dead after the helicopter was downed.

Now, Mendez is afraid that the guerrillas will come looking for him. It is the same fear that has kept many witnesses to atrocities -- by both government forces and the leftist rebels -- from coming forward in the course of this country's 11-year-old civil war.

But in Mendez's view, he had little choice.

"I'm very nervous," he said. "But I had to do it. I was very close. I can't deny the truth. Others who live farther away can say they didn't see anything. But I can't lie."

A 34-year-old father of five, Mendez spoke with two American reporters today on the steps of his in-laws' house, a few hundred yards from the charred remains of the U.S. Army UH-1 Huey transport helicopter. It is the same hamlet where he was born and reared. He returned to it two years ago after living for three years in Dallas, where he worked as a dishwasher in a hotel.

Although Mendez has spoken about the incident with reporters and neighbors, he said he has not discussed it with any officials, either from the United States or the Salvadoran military. No one has pressed him, and no one has suggested his story is false.

In a clear, matter-of-fact voice, Mendez said he was fetching water for his cattle about 2 p.m. Wednesday when the helicopter came flying overhead. From the ground, the guerrillas of the Farabundo Marti National Liberation Front (FMLN) unleashed a burst of machine-gun fire lasting, Mendez said, about 10 seconds.

After that, he said, the helicopter "fell like a bomb." At no point did he see the helicopter fire on the rebels, as the FMLN has asserted. At first, frightened, he ran into his father's house, about 400 yards from the crash site. But about 20 minutes later, the rebels approached the house asking for help in removing the Americans and their equipment from the helicopter.

When he arrived on the scene, the pilot, identified later as Chief Warrant Officer Daniel S. Scott, was already dead, said Mendez. But the two other Americans were alive and talking. One of them, Pfc. Earnest G. Dawson Jr., had a large gash in his chin and other injuries but was able to walk with help, Mendez said.

About 20 guerrillas were on the scene, equipped with assault rifles and carrying radios. When he approached the two living Americans, they spoke to him in English. Having lived in the United States for three years, Mendez mustered a few words of English to communicate.

The men were both hurt, he said, but "not at the point of dying."

"When I went to help one of them, he said not to move him," he said. "One asked for water -- he used the word agua."

With at least one other peasant, Miguel Angel Carranza, Mendez walked down a rugged slope toward the small river that snakes below his in-laws' house. Four rebels stayed with the Americans and their helicopter, of whom Mendez recognized two. He identified them by their noms de guerre: "Ulises" and "Aparicio."

They had been gone perhaps two or three minutes, he said, when about four shots rang out.

"I didn't think anything, but we ran for about five minutes . . . because in the moment of panic you don't think -- you just run."

After a few minutes, he returned to the crash site to find the two Americans dead. There were fresh bullet holes in their heads, he said.

Asked if he thinks the guerrillas murdered the Americans, Mendez responded, "I imagine so." He added: "We're very afraid. . . . I've given more details than the others. They'll know it was me."

Although Mendez has land, cattle and a 6-month-old son here, he is thinking about leaving. "It would be a pity to lose all this . . . but if the atmosphere gets bad, it'd be better for me to leave."

The three slain Americans are Dawson, 20, Scott, a 39-year-old father of five, and Lt. Col. David H. Pickett, a 40-year-old father of three. They were on their way back to Honduras after a supply mission, U.S. officials say.

Their flag-covered coffins were loaded into a military aircraft today for Dover Air Force Base, Del. Ambassador William G. Walker said, "Those who committed this act, who murdered our colleagues, perpetrated a war crime."

Using nearly the same words he used after six Jesuits were killed in San Salvador 14 months ago, Walker added, "I have asked the question before {and} it bears repeating today: What kind of animals would execute injured, helpless and nonthreatening persons in their power, and do so in cold blood?" Eight Salvadoran military men have been charged in the Jesuits' deaths.

Walker went on to call for justice for the rebels responsible for the Americans' deaths.

The FMLN, which has acknowledged shooting down the copter, today issued its fourth statement on the incident since Wednesday. It appeared to back away from earlier outright denials of the American allegation that guerrillas killed the men on the ground.

"We have begun an exhaustive investigation to clarify the whole truth of this incident," the rebels said in a clandestine radio broadcast. "The FMLN has a clear policy, to assume responsibility for all of its acts and that is how we will proceed in this new situation."