Suppose the unthinkable happened, and terrorists struck New York or another big city with an atom bomb. What should people there do? The government has a surprising new message: Do not flee. Get inside any stable building and don’t come out till officials say it’s safe.

The advice is based on recent scientific analyses showing that a nuclear attack is much more survivable if you immediately shield yourself from the lethal radiation that follows a blast, a simple tactic seen as saving hundreds of thousands of lives. Even staying in a car, the studies show, would reduce casualties by more than 50 percent; hunkering down in a basement would be better by far.

But a problem for the Obama administration is how to spread the word without seeming alarmist about a subject that few politicians care to consider, let alone discuss. So officials are proceeding gingerly in a campaign to educate the public.

“We have to get past the mental block that says it’s too terrible to think about,” W. Craig Fugate, administrator of the Federal Emergency Management Agency, said in an interview. “We have to be ready to deal with it” and help people learn how to “best protect themselves.”

Officials say they are moving aggressively to conduct drills, prepare communication guides and raise awareness among emergency planners of how to educate the public.

Over the years, Washington has sought to prevent nuclear terrorism and limit its harm, mainly by governmental means. It has spent tens of billions of dollars on everything from intelligence and securing nuclear materials to equipping local authorities with radiation detectors.

The new wave is citizen preparedness. For people who survive the initial blast, the main advice is to fight the impulse to run and instead seek shelter from lethal radioactivity. Even a few hours of protection, officials say, can greatly increase survival rates.

Administration officials argue that the cold war created an unrealistic sense of fatalism about a terrorist nuclear attack. “It’s more survivable than most people think,” said an official deeply involved in the planning, who spoke on the condition of anonymity. “The key is avoiding nuclear fallout.”

The administration is making that argument with state and local authorities and has started to do so with the general public as well. Its Citizen Corps Web site says a nuclear detonation is “potentially survivable for thousands, especially with adequate shelter and education.” A color illustration shows which kinds of buildings and rooms offer the best protection from radiation.

In June, the administration released to emergency officials around the nation an unclassified planning guide 130 pages long on how to respond to a nuclear attack. It stressed citizen education, before any attack.

Without that knowledge, the guide added, “people will be more likely to follow the natural instinct to run from danger, potentially exposing themselves to fatal doses of radiation.”

Specialists outside of Washington are divided on the initiative. One group says the administration is overreacting to an atomic threat that is all but nonexistent.

(Read More: NY Times)