The leftist Farabundo Marti National Liberation Front has promised its own investigation into the alleged reb-el execution of two U.S. airmen after their helicopter was downed.

The incident has led to calls in Washington for the restoration of military aid to El Salvador's rightist government."Those who committed this act, who murdered our colleagues, perpetrated a war crime," U.S. Ambassador William Walker said Sunday.

In Washington, Secretary of State James A. Baker III said he would ask Congress to end restrictions on military aid to the Salvadoran government.

The country's senior Roman Catholic official said a church inquiry lends support to U.S. claims that two of three U.S. soldiers were shot and killed after their chopper was downed by rebels Wednesday.

The rebels' clandestine Radio Farabundo Marti on Sunday dropped earlier denials and promised "an exhaustive investigation" of the incident.

The radio said the rebel group has "a clear policy of assuming responsibility for each one of its acts, and we will proceed in that manner in this new situation."

Rebel officials at first claimed all three soldiers had died when the helicopter crashed. They later said all had died of crash injuries shortly after the helicopter went down.

They also claimed that guerrillas had fired at the helicopter only after it fired at a local village - an allegation denied by U.S. officials. The helicopter was shot down by small arms fire from members of the rebel group.

At a memorial ceremony at Comalapa airport, 35 miles south of the capital of San Salvador, Walker said: "We are determined to see those responsible for the deaths of these Americans brought to justice."

Later, a U.S. Air Force C-130 transport plane took off for the United States carrying the bodies of Lt. Col. David H. Pickett, 40; Chief Warrant Officer Daniel S. Scott, 39; and Pvt. 1st Class Earnest G. Dawson, 20.

U.S. officials said Saturday that preliminary autopsies indicated that only Scott had died in the crash itself. They said Pickett and Dawson were shot with at least three different weapons as they lay injured at the crash site.

"What kind of animals would execute injured, helpless and nonthreatening persons in their power, and do so in cold blood?" Walker asked.

President Alfredo Cristiani, who attended the memorial service, also promised to try those involved in the deaths.

"We will do everything possible so that those guilty of this infamous murder receive punishment . . . according to the law," Cristiani said.