After the bomb blast on Sunday, jubilant Iraqis danced on the flaming wreckage of the contractors' vehicles, witnesses in the flashpoint Iraqi town said.
The two deaths come on an unprecedented day of bloodshed for the US army. Sixteen US soldiers were killed in Iraq on Sunday, 15 when a helicopter was shot down and one in a Baghdad bomb blast.
"Clearly it is a tragic day for Americans," US Defence Secretary Donald Rumsfeld told ABC television. "In a long hard war we are going to have tragic days."
Falluja residents said the roadside bomb had hit a convoy of US personnel in civilian vehicles. At least one vehicle was ablaze at the scene, where celebrating crowds shouted anti-US slogans.
Television pictures showed a gleeful youth wearing a US army helmet; others danced on wreckage.
Falluja lies in the restive north-central region of Iraq, which has seen the most active restance to the US-led occupation of the country.
The shooting down of the Chinook helicopter south of Falluja as it carried US troops to Baghdad was also hailed by locals.
"The Americans are pigs. We will hold a celebration because this helicopter went down - a big celebration," said wheat farmer Saadun Jaralla near the crash site.
"The Americans are enemies of mankind."