SAN SALVADOR, JAN. 4 -- U.S. military forensic and technical experts today examined the bodies of three American servicemen and combed the wreckage of their helicopter, and photographs and videotape appeared to support the Bush administration's suggestion that at least two of the soldiers had been executed.

The photos and videotape, viewed by The Washington Post, clearly show what appear to be bullet wounds to the temples and faces of two of the men. The third man, the pilot, is believed to have been fatally wounded when the helicopter was shot down by leftist guerrillas in El Salvador Wednesday.

U.S. officials said Thursday that preliminary evidence suggested that the Salvadoran guerrillas of the Farabundo Marti National Liberation Front (FMLN) had executed the servicemen after the helicopter made a "controlled landing."

The guerrillas, who claimed responsibility for shooting down the helicopter over a "war zone" in eastern San Miguel province, have denied executing the Americans, saying they died of wounds sustained in the crash.

Today, in their third communique on the incident, the rebels said the American helicopter was shot down after it fired on guerrillas and civilians on the ground. An FMLN spokesman in Mexico City called for an autopsy by an "independent forensic commission" to determine the cause of the Americans' deaths.

U.S. officials said there was no evidence to suggest that the helicopter ever fired its M-60 machine gun. They noted that helicopter crews have standing orders not to discharge their weapons except in dire emergencies. The servicemen had been on a routine supply mission from Honduras, one of about four such flights daily to support U.S. military advisers in El Salvador.

The dead soldiers were identified as Lt. Col. David H. Pickett, Chief Warrant Officer Daniel S. Scott and Pfc. Earnest G. Dawson Jr. All were assigned to the 4th Battalion, 228th Aviation Regiment at Soto Cano air base in Honduras. The bodies are to be taken by U.S. military transport plane on Sunday, possibly to Dover Air Force Base, Del.

The three-person forensic team -- two pathologists and a photographer from the Armed Forces Institute of Pathology -- arrived in El Salvador from Washington Thursday and began examining the bodies today. They were expected to finish their work by late tonight.

Two helicopter safety experts from Fort Rucker, Ala., the Army's safety and aviation training center, and two other technical specialists from the U.S. Army South in Panama also spent the day examining the wreckage of the U.S. Army UH-1 Huey transport helicopter, which reportedly was set ablaze by the rebels after they shot it down.

The specialists are trying to determine the cause of the crash and fire, and the helicopter's speed on impact. Those determinations would help to settle the question of whether the servicemen could have survived the crash landing.

Peasants in the rugged area where the helicopter went down, about 75 miles east of the capital, said two of the Americans were wounded but able to ask for help and water.

Several of the peasants, in videotaped testimony given to the Salvadoran armed forces late Wednesday, said they began to assist the two surviving Americans as seven to 10 guerrillas looked on.

They said the rebels first removed the Americans' equipment, including the M-60 machine gun, from the helicopter. Then, when the Americans asked for water, the guerrillas led the peasants away, ostensibly to fetch water.

However, one rebel soldier stayed behind with the Americans, according to two of the peasants' testimony. Moments later, several shots were heard, the peasants said.

In the testimony, videotaped at the Salvadoran army base in San Miguel soon after the bodies were recovered by Salvadoran troops, one of the peasants, Miguel Angel Carranza Andrade, stood over the uncovered bodies of the Americans.

Carranza, vice president of a local citizens council, said he returned to the crash site a few minutes later and saw that the two Americans had new injuries and were dead.

"He didn't have this wound, or this one either," he said, pointing to what appear to be bullet entrance and exit wounds to Pickett's head. "But when I came back, he had them."

Pointing to Dawson's body, Carranza said that when he left, the American had a large gash on his chin but was alive. But indicating an apparent bullet wound to the face, he added, "He didn't have this one."

In the guerrillas' initial version of the event, they said in a clandestine radio broadcast at about 5 p.m. Wednesday, about three hours after the helicopter was downed, that the three Americans' bodies were found in the helicopter wreckage.

On Thursday, the People's Revolutionary Army, the hard-line guerrilla faction operating in the San Miguel region, said rebels downed the helicopter because they thought it was a Salvadoran aircraft and was going to fire on them. They said one American died immediately and the other two, gravely injured, died shortly afterward.

In an interview today, Miguel Saenz, a senior FMLN official in Mexico, said the allegation that the Americans were executed was a fiction designed to release $42.5 million in U.S. military aid to the Salvadoran government. The funds were frozen last year pending both sides' conduct in the war and progress toward a negotiated settlement.

President Bush is scheduled to recommend to Congress in the coming days whether to release the aid. Bush could recommend restoring the aid if he finds that the rebels have committed human rights violations.

Special correspondent Andrea Dabrowski in Mexico City contributed to this report.