If North Korea fired a long-range missile at the United States today -- like the one it test-fired this summer -- could we defend ourselves?

Until recently, the answer would have been an unequivocal "no." But that answer is changing as America moves, very slowly, toward deploying a missile-defense system. As Air Force Lt. Gen. Henry Obering, director of the Missile Defense Agency, noted in the wake of a successful test last month, we now stand "a good chance" of shooting down a missile that threatens our country.

Make no mistake: We're far from safe. But we're better off now than we were in the Cold War days of "Mutually Assured Destruction."

The fittingly named MAD policy dates to the early 1970s, when the United States and the Soviet Union were the principal nuclear powers. To discourage each side from firing its weapons first, both signed a treaty promising never to deploy an effective missile defense.

But the Soviet Union collapsed 15 years ago. And the world has long been a different place. For one thing, the nuclear threat has spread widely. There are five "official" nuclear powers and at least two de facto ones, including India and Pakistan. Several others are suspected of having nukes. And that number will only increase.

Iran, for one, has an aggressive nuclear program. For "peaceful purposes," its president insists. But while advanced industrial countries such as Japan and the United States do indeed need electricity from nuclear power, Iran is the world's second-largest oil producer. It doesn't need nuclear technology to produce power -- Iran wants it so the country can project power. An Iran with nuclear missiles could dominate the Middle East and directly threaten strategic American allies.

And then there's the unpredictable Stalinist regime in North Korea.

On July 4, it launched several test missiles, including the long-range Taepodong-2. North Korea says it's a nuclear power. It's not difficult to imagine that country, which has been collapsing for years, lashing out at some imagined slight by firing a nuclear warhead at the United States. And we'd have only a minimal chance of defending ourselves. Today only 11 test interceptors are deployed to protect the U.S. mainland.

We have the ability to change that.

An effective missile defense will require three types of systems: the land-based interceptors positioned in California and Alaska; sea-based interceptors (to defend U.S. coastal areas and our allies against short-range ballistic missiles launched from ships), and, critically, space-based interceptors.

That last category is the most controversial.

Opponents complain that we shouldn't "weaponize" space. But that ignores the simple fact that space is already weaponized. After all, if a country fires a long-range missile, that missile has to pass through space. So it only makes sense to place platforms up there to destroy missiles before they can re-enter the atmosphere and threaten Americans.

We already have some of the technology in place. Until the Clinton administration cancelled the Brilliant Pebbles program, it was making great strides. That program can and should be revived and expanded, so we can begin testing and deploying effective space-based interceptors as soon as possible.

Twenty five years ago this week, President Ronald Reagan vowed to "end our long neglect of strategic defenses." Since then, though, we've taken only small steps. We're not defenseless -- our missile system has passed several tests. And last week, the military activated a high-powered radar outpost in Japan to help it track ballistic missiles in that region.

But with nuclear technology in the hands of unstable regimes, we're not as safe as we should be. We'd be crazy -- MAD, even -- not to deploy a layered defense screen that can protect all Americans.

Edwin Feulner is president of The Heritage Foundation (heritage.org), a Washington-based public policy research institute and co-author of the new book Getting America Right.