WASHINGTON — Analysts told a Senate committee on Tuesday that the federal government is not prepared to respond if terrorists were to detonate a small nuclear bomb in the heart of Washington, D.C.

Five witnesses testified before the Senate Homeland Security and Governmental Affairs Committee about the effect a 10-kiloton nuclear bomb – the same size as the weapons dropped on the Japanese cities of Hiroshima and Nagasaki during World War II – would have if it exploded at the White House.

Sen. Joseph Lieberman, I-Conn., chairs the panel, and Sen. Susan Collins of Maine is the committee’s top Republican.

“The scale of this disaster would quickly overwhelm even the most prepared city and state governments,” Ashton Carter, a former Clinton Administration official and Harvard professor, told the Homeland Security and Governmental Affairs Committee.

“The federal government must step up to the inevitable fact that this will overwhelm state and local responders. A nuke weapon is uniquely destructive. Nothing does what these things do,” he said. “[It demands] the full federal response.”

Dr. Cham Dallas, a public health expert at the University of Georgia, presented a map of downtown Washington, D.C., showing that there would be 100,000 deaths within just a few square miles of the White House.

Casualties would extend from the Washington Monument through Georgetown and north toward the Washington Zoo. There would be massive debris from damaged buildings, including shattered glass.

In Chicago or New York City, which have more concentrated populations, the damage could be four to eight times as bad.

Collins quizzed the officials about whether American hospitals were prepared to handle mass casualties.

Dallas said hospitals would be overwhelmed and susceptible to criminals who would try to steal drugs from the pharmacy, adding that the average age of hospital guards is 68 and almost all are unarmed.