Andrew Rose and Loyd Holliman each pleaded guilty in federal court to soliciting and receiving bribes as public officials, prosecutor Jim Letten said.
They each face up to 15 years in prison and a $250,000 fine at sentencing July 26.
The volunteer firefighters came to New Orleans to help with search-and-rescue operations after Hurricane Katrina struck on Aug. 29.
They signed on with FEMA and were put to work managing a camp housing disaster relief workers in the city's Algiers neighborhood, one of the men's attorneys has said.
Prosecutors said the pair allegedly approached a local contractor and offered to inflate the head count for meals at the camp in exchange for a payoff. The contractor held a meal service contract, and would earn more money if the head count were inflated.
The contractor reported the offer to the FBI.
The men, both from Colorado, were arrested Jan. 27 after receiving two envelopes containing $10,000 each, prosecutors said.