It's appropriate, in a way, that North Korea chose the Fourth of July to test-fire several missiles into the Sea of Japan. That's the day we celebrate our independence, and Pyongyang's saber-rattling shows the need for us to take further steps to secure independence from the threat of missile attack.

If the intercontinental ballistic missile (ICBM) launched by North Korea had been aimed at Alaska or the West Coast of the United States, our missile-defense system - on alert for weeks in anticipation of the launch - might have been able to destroy the missile. We have 11 ground-based interceptors (nine in Alaska and two in California) now in place to counter long-range missiles.

But success in this endeavor wouldn't be assured - for our missile-defense system is fairly limited, particularly for countering missiles of this type.

First, the system is still under development - although some of it is operational. Second, beyond those 11 ground-based interceptors, we have little. The Navy seeks to field up to 20 Standard Missile-3 (SM-3) interceptors on four Aegis ships by the end of this year, says Lt.-Gen. Henry Obering, director of the Missile Defense Agency. But those interceptors are designed to counter medium-range missiles.

And the system's coverage is spotty. If North Korea had fired the long-range missile at Alaska or our West Coast, interceptors would have been in position to counter it. But if the missile were aimed at, say, Australia - an ally we're treaty-bound to protect - our ground-based interceptors would've been in poor position to respond.

And if North Korea launched a medium-range missile at Japan or Guam, our best hope of success would be an SM-3-bearing ship fortuitiously positioned to launch an intercept.

In any instance, we would certainly do our utmost if a launch threatened the United States or an ally - but we have a lot of work to do to be secure against missile attacks.

This need not have been the case. As far back as February 1991, Stephen Hadley (now national security adviser to President Bush but then an assistant secretary of defense for international security policy) presented a missile-defense plan along with Ambassador Henry Cooper, then director of the Strategic Defense Initiative Organization.

The system they proposed - GPALS, for Global Protection Against Limited Strikes - would be at least partially complete now if Congress hadn't killed the plan soon thereafter.

GPALS would've been capable of defending against up to 200 individual missile re-entry vehicles. The plan called for a family of defensive interceptors to counter short- and medium-range missiles, ground-based missile defenses for countering long-range missiles and a broader sensor network and command-and-control system. By now, far more than 11 ground-based interceptors would have been in place.

And they would've been bolstered by a constellation of space-based interceptors called Brilliant Pebbles - basically, computer-guided meteorites - which could have fended off all long-range and most short- and intermediate-range missiles. Brilliant Pebbles would have allowed multiple shots at the kind of missile North Korea test-fired on Tuesday. Even if the full compliment of each element of GPALS were not deployed today, we'd have been well-protected against any target - within the United States or elsewhere - that the North Koreans might choose to attack.

In 1991, when the GPALS plan was unveiled, its cost was estimated at $41 billion (in 1988 dollars). We'll never get the protection we need for that price now.

Yet we still need the system - perhaps now more than ever. The North Korean situation provides a perfect example of why. Do we bomb the launch pad at risk of getting it wrong and/or inflaming world opinion against us? Or must we wait for loss of life and property before acting against the threat?

A defensive option against missile attack is essential. It provides the president with a wider variety of choices in a world where nuclear weapons and ballistic-missile delivery systems are proliferating and where future events are difficult to predict.

It is long past time that Congress make up for its past failings and fund a missile-defense architecture similar to GPALS. Only then can we be independent of the fear of missile attack.

Baker Spring is the F.M. Kirby Research Fellow in National Security Policy in the Douglas and Sarah Allison Center for Foreign Policy, at The Heritage Foundation