ROBERT SIEGEL, host: Well, now to what the New START treaty does cover. Here's the headline number. The U.S. and Russia will each have to reduce their stockpiles of deployed long range nuclear warheads from 2,200 to 1,550, which got us wondering, what happens to those extra weapons?

And to help us answer that and other practical questions about the implementation of New START, we turn to George Perkovich, director of the nuclear policy program at the Carnegie Endowment for International Peace. Welcome to the program once again.

Mr. GEORGE PERKOVICH (Nuclear Policy Program Director, Carnegie Endowment for International Peace): Thank you.

SIEGEL: And as we've heard, each country could soon find itself with hundreds of deployed warheads over the limit. What does the treaty require that they actually do with those? Destroy them? Store them? What?

Mr. PERKOVICH: Well, the treaty gives the two countries seven years to implement. Also, the way that the reductions actually are done physically focuses much more on the delivery system. So, you mentioned the number that we would reduce down to 1,550 deployed warheads. The warhead is the part that goes boom.

But to be a weapon it has to get to the target. And it's the delivery systems, the delivery vehicles that get it there, namely, missiles that are based on submarines, missiles that are based in silos, less likely would be on heavy bombers. It's those things, the delivery vehicles, that are dismantled, basically, if not destroyed, rendered unusable and that process is verified.

SIEGEL: Now, the dismantling of a missile is fairly easy to visualize, but a strategic bomber or a submarine that launches nuclear missiles, would such systems actually be dismantled?

Mr. PERKOVICH: They can be, or they can be retired due to age. But the more likely way that this would be done is that you render, like, our submarines, for example, have 24 tubes, which basically look like tubes into which you could put a missile. You could render those useless by filling them with concrete or otherwise disabling them. And then that part of the reductions, as it were, is what's actually kind of counted and verified more than the warheads themselves.

SIEGEL: But just to clarify this point, as a result of reductions, of deployed warheads of this sort, each side, Russia and the U.S., would have an increase in the number of somewhere stored warheads and something that could be conceivably used once again in weapons.

Mr. PERKOVICH: That's correct. And, in fact, one of the challenges, and it was mentioned in the earlier piece in the future, or hopefully a next round, is to for the first time have in arms reductions treaties the verification of the dismantlement of warheads. And I think that's something that both sides, U.S. and the Russians will start to think pretty seriously about going forward.

SIEGEL: I would think that despite the umpteen thrillers and James Bond-like stories about stolen ICBMs and submarines that are hijacked with nuclear missiles aboard, it really is the much smaller weapons that are much more likely to get into bad hands. And when we think of loose nukes, it's not really so much an entire missile that we think is going to go missing.

Mr. PERKOVICH: Right. There's a kind of a joke that some of the people who are in the nuclear business, you know, make, which is, you know, the safest, most secure place for a nuclear weapon, a nuclear warhead is on top of a missile in a silo.

SIEGEL: Well, George Perkovich, thanks for talking with us about it.

Mr. PERKOVICH: Thank you.

SIEGEL: Thats George Perkovich, who is director of the Nuclear Policy Program at the Carnegie Endowment for International Peace.