The State Department suspects leftist rebels executed three American servicemen in El Salvador but is awaiting the outcome of an investigation by a U.S. forensic team before making a final judgment.

The incident Wednesday could have an impact on future U.S. aid levels to the Salvadoran military. President Bush is expected to decide next week whether to release $42.5 million in such aid set aside by Congress last fall.The three Army crewmen were flying on a routine mission from San Salvador to Honduras when their helicopter was struck by gunfire, State Department deputy spokesman Richard Boucher said Thursday. There are differing versions as to what happened next.

"The helicopter landed in a controlled fashion. Nevertheless, all three U.S. servicemen had apparent gunshot wounds to the head and two of them had no other apparent wounds," Boucher said.

Privately, a U.S. military source said there was no doubt that the three Americans were victims of an execution. But this account was contradicted by the FMLN rebels, who said they found the bodies of the Americans inside the aircraft after it hit the ground.

An eyewitness said two of the Americans were alive when the helicopter landed and that the rebels showed no sign of wanting to harm the crewmen. The eyewitness, however, was not present when the Americans died.

Associated Press photographer Mike Stravato, who visited the crash site, said the helicopter clearly crashed, and did not land safely.

The bodies were recovered by the Salvadoran armed forces and taken to San Salvador, the Pentagon said.