WASHINGTON —  Two senators on Thursday asked federal officials to explain their decision to sign a $236 million deal with Carnival Cruise Lines (search) for Hurricane Katrina housing, saying Greece was ready to provide two ships for free.

In a letter, Sens. Tom Coburn, R-Okl., and Barack Obama, D-Ill., asked Homeland Security Secretary Michael Chertoff to explain why Federal Emergency Management Agency officials chose Carnival and turned down the Greek offer.

The six-month deal with Carnival for three full-service cruise ships — which now sit mostly empty in the Gulf Coast (search) — has been criticized by lawmakers of both parties as a prime example of wasted spending in Hurricane Katrina-related contracts.

The two have proposed legislation that would create a chief financial officer to oversee and approve Katrina spending.

"Even if the Carnival contract were a good one — and it almost certainly is not — it is inexplicable why FEMA would fail to implement the Greek governments offer of free cruise ships," the senators wrote.

Greece on Sept. 4 offered to donate two cruise ships to the United States as part of humanitarian aid for Katrina evacuees, according to the European Union.

Butch Kinerney, a spokesman for FEMA, said the agency signed an initial deal with Carnival by Sept. 3 — before the Greek offer. He said he did not know when FEMA officials subsequently became aware of it.

Once FEMA officials did find out, they chose to move forward with the Carnival deal because it was not known how quickly Greece could provide the ships, Kinerney said.

John Hart, a spokesman for Coburn, said the senators want to know exactly when FEMA became aware of Greece's offer and why the agency hasn't tried to back out of the Carnival deal, particularly since the ships are hardly being used.