By Sasha Chavkin, ProPublica

As Japan struggles to contain its growing nuclear crisis, a congressman and a disaster-preparedness expert raised concerns that the United States is not prepared to respond to a nuclear disaster.

Rep. Ed Markey, D-Mass., wrote a letter to President Obama on March 13 saying that the federal government lacks a coordinated plan for responding to a major nuclear incident. Markey wrote that key agencies tasked with emergency response in the event of a nuclear disaster are unclear about what their roles would be and even about which agency would be in charge.

"It appears that no agency sees itself as clearly in command of emergency response in a nuclear disaster," Markey wrote.

Dr. Irwin Redlener, the director of the National Center for Disaster Preparedness at Columbia University, echoed Markey's assessment, saying current disaster-response plans are confusing and leave too much uncertainty.

"It's definitely not as clear as it needs to be," Redlener said. "Part of the problem is a tremendous overlap on the federal, state and local levels."

The White House says that the lead agency in responding to a potential nuclear disaster depends upon the source and the nature of the nuclear release. It says federal disaster-response plans clearly establish which agency would be in charge under different scenarios. For example, the Nuclear Regulatory Commission would lead the response to a release from a nuclear power plant, the Department of Energy would coordinate response to a crisis involving nuclear weapons in its custody, and the Department of Homeland Security would lead the response to a deliberate attack.

"Given the range of potential causes, from an earthquake to a terrorist attack, the plan provides the flexibility and agility we need to respond aggressively and effectively," said White House spokesman Nicholas Shapiro in a statement.

The contingency plan cited by the White House includes six different agencies that could potentially be in charge of nuclear emergency response. A table that details which agency takes the lead has 15 different scenarios, eight of which include more than one possibility for which agency would coordinate the response.

Columbia's Redlener said that this setup is problematic: It would result in "people trying to make ad hoc decisions in the midst of a crisis." Redlener said that officials in these circumstances might hesitate to make decisions because of uncertainty about their legal authority to act.

In his letter to Obama, Markey wrote that officials from the Nuclear Regulatory Commission and EPA who briefed his staff were confused about their roles and about which agencies should be taking the lead.

"One Agency official essentially told my staff that if a nuclear incident occurred, they would all get on the phone really quickly and figure it out," Markey wrote.

The White House said that state and local officials, as well as nuclear facilities, all had detailed response plans in place. Shapiro, the White House spokesman, said that there is "a robust and active nuclear power plant accident exercise program" that involves authorities at different levels of government, and that such an exercise was conducted last year.

But Redlener said that the country was not prepared for critical elements of responding to a nuclear disaster, including mass evacuations, addressing the needs of vulnerable populations such as children, the elderly and the disabled, and distribution of potassium iodine in areas where it is not stockpiled. (See our story questioning how much protection iodine pills could offer.)

"If you look back at what happened in the Gulf after Katrina, I think that's a pretty good demonstration of the capacity we have," Redlener said. "We need to do a much better job in terms of imagining and planning for large events."