The Obama administration is faced with one of those damned-if-you-do, damned-if-you-don’t decisions: Should it be giving Americans advice on what to do in case of a nuclear attack by terrorists on an American city?

Nobody wants to cause a panic, and nobody is saying that a suitcase (or cargo container or whatever) bomb is an imminent threat.

On the other hand, if the administration ignores the possibility altogether, and something catastrophic does happen, and the administration hasn’t widely disseminated simple information that could save thousands of lives, it would make what happened to George W. Bush after Hurricane Katrina look like a coronation.

So the administration is doing what President Barack Obama is wont to do, anyway: splitting the difference. It has begun distributing to emergency preparedness officials around the nation a planning guide on how to respond to an isolated nuclear attack. And it has begun distributing similar information to the public on the Federal Emergency Management Agency’s Citizens Corps website.

Here, as they say, is the takeaway: Ignore the impulse to run away. Stay inside, even if it’s inside your car. And if you are inside, go as deep into the basement as possible and stay there for at least a couple of hours.

“Shelters such as houses with basements, large multi-story structures, and underground spaces (e.g., parking garages and tunnels) can generally reduce (radiation) doses from fallout by a factor of 10 or more.”

So it says in the “Planning Guidance for Response to a Nuclear Detonation.” It is fascinating reading, full of grim acronyms like “LD50” (a lethal dose or radiation that kills 50 percent of a population) and “RTR” (Radiation Triage, Treatment and Transport).

It assumes, for sake of argument, that terrorists would acquire a 10-kiloton nuclear device, the explosive equivalent of 10,000 tons of TNT, only worse because TNT doesn’t create radioactive fallout.

A 10-kiloton nuclear weapon creates a fireball 650 feet wide. Anything within a kilometer (six-tenths of a mile) of ground zero will be flattened or heavily damaged by the shock wave or wind.

Outside of this “no-go” zone and within a mile of ground zero, there will be heavy structural damage but “many serious injuries (and) greatest lifesaving opportunities.”

Outside of a mile, you have a pretty good chance of surviving, provided you head for the basement or stay in your car. Fallout will be a serious problem as far as 20 miles away, depending on winds, for up to 72 hours, depending on how close you are to the blast.

Also, the report says, local emergency responders shouldn’t expect any substantial federal help for at least 24 hours, and perhaps as long as 72 hours.

How much should people worry about this? Not much. What are the odds?

But it is a good thing that some people are worrying about it.