Ex-astronaut Rusty Schweickart wants to save the world from an incoming asteroid -- the multimegaton variety blamed for killing the dinosaurs -- and he thinks that the only sure-fire way to keep them away is by using, of all things, diplomacy.

Mr. Schweickart was on the Apollo 9 mission that circled the earth testing the lunar lander, and had a successful post-NASA career in business. Now 72, he is spending his retirement trying to alert the world to the problem of Near Earth Objects, or NEOs.

Most of the time, he conducts the campaign sitting at a laptop computer in the study of his home in the Sonoma County wine country of Northern California. The Web connects him to a global network of other ex-astronauts, astronomers, government scientists, space buffs and more. Many of them are members of the B612 Foundation, which Mr. Schweickart helped to found to research the problem.

Asteroids have been studied for centuries. But there are still so many gaps in our understanding of them that Mr. Schweickart says he has had to pioneer a lot of asteroidology himself. He tells me, "You are looking at the world's expert in deflecting asteroids, and that is just inexcusable."

The basics of the problem are familiar to Discovery Channel viewers. Now and then, one of the millions of chunks in the Asteroid Belt gets knocked into a different orbit, one that might one day lead to a collision with Earth.

The best place online to follow all this is at neo.jpl.nasa.gov, where Mr. Schweickart himself checks in several times a day. It's a kind of Facebook for asteroids, each one having its own home page, along with a cool Java applet showing its orbits.

When it comes to actually dealing with an asteroid, the Hollywood option, of nuking it to smithereens, is the least useful, says Mr. Schweickart, largely because you can't control the debris.

Serious students of the topic prefer the idea of crashing a spacecraft into the asteroid, thus nudging it into a new orbit. In fact, merely orbiting a spacecraft nearby might do the same trick, on account of the craft's gravitational pull.

Because asteroids have these sorts of easily imagined happy endings, it's a more pleasant apocalypse to contemplate than, say, global warming, for which there is no such easy solution.

Deadly asteroids also have something else going for them: They can be dealt with for a relatively small amount of money. Spending $100 million or $200 million a year for a decade will put in place all the telescopes necessary to have a complete census of all of the NEOs that threaten Earth. (Current efforts, of which there are several, tell us about only a fraction of them.) Such a tracking program would likely give us a warning time of decades ahead of any possible collision.

The hard part of asteroids, says Mr. Schweickart, and the part he is spending nearly all of his time on right now, involves finding a way to reach a global agreement on how the planet would respond should an asteroid head our way.

This is where the astronaut starts to think like a diplomat. Indeed, several of the messages in his inbox last week involved a meeting he's hoping to have in the fall with the secretary-general of the United Nations.

Mr. Schweickart knows what you're probably thinking at this point: That eliminating an asteroid is a job for Bruce Willis, not for a bunch of diplomats. Hence, a short lesson from Mr. Schweickart, him with an MIT degree, in orbital mechanics.

When an object like an asteroid is known to be heading toward Earth, its exact splashdown point can't be calculated with any certainty. Instead, scientists know only that it will fall someplace on a thin line along the Earth's surface. These are the sorts of trajectories that make news when wayward satellites drop back to terra firma.

Now suppose the impact line for an asteroid begins over Country A, extends through Country B and ends at Country C. To nudge the asteroid so that it misses Earth completely, you first have to push it in one direction or another -- in effect, toward either A or C. That means that residents of either A or C will bear a slightly greater risk if the rescue effort doesn't push the asteroid quite hard enough.

Naturally, the citizens of A and C, and their political leaders, will be screaming for the asteroid to be pushed in the other country's direction and out of their backyard.

Mr. Schweickart says the only fair way to proceed is to have a decision-making formula drawn up well in advance, thus unaffected by the political heat of an actual crisis.

Another reason to involve the U.N., says Mr. Schweickart, is to overcome global suspicion that a unilateral American antiasteroid effort would be a ruse to militarize space. Mr. Schweickart says he also is concerned about the issue. Many in Washington, he says, seem almost exclusively interested in the nuclear option.

Mr. Schweickart has been working on NEOs since 2001, and says he will spend another year on the project before turning the reins over to someone else. In the meantime, he's talking to everyone he can.

"Let's face it," he says, "being an ex-astronaut opens a lot of doors for you."