To hear some critics tell it, America's planned missile-defense system is based on the B-movie fantasies of former actor President Reagan. It'll never work, they chortle. But anyone who keeps up with the latest tech news knows better.

For example, NASA scientists recently landed a space probe on an asteroid 196 million miles from earth. The feat was like flying through the blades of a moving propeller, one NASA engineer told The Washington Post, because the asteroid is tiny-just twice the size of Washington, D.C.-has practically no gravity to attract the probe, and revolves once every five hours and 17 minutes. Hitting "a bullet with a bullet," the task facing missile defense scientists and engineers, is a cakewalk by comparison.

Then there are the "smart cars." Researchers at DaimlerChrysler are developing crash-proof cars that use satellite tracking systems and computers to maintain a safe distance between other autos. The cars, slated to become available in the next few years, will be able to take control from drivers in an emergency and independently plot the fastest course through traffic.

In Hawaii, the U.S. Air Force and IBM are working with a supercomputer that can find dead satellites, spacecraft and unidentified flying objects by turning blurry telescopic images into clear pictures in seconds. It's said to be so good it can find a lost screwdriver floating among 40 years of space junk. And still we're told that finding a warhead amid a field of decoys is beyond our capabilities.

Spacecraft landing on asteroids millions of miles away. Cars that can see approaching traffic in all directions. Computers that can locate a tiny piece of space junk instantly. American know-how can surmount virtually any obstacle. Yet we're to believe that missile defense is impossible?

Baloney. The Navy alone has been using a "theater" missile-defense system for more than 20 years to protect its ships and planes from cruise missiles. The Navy brass and their Pentagon bosses swear by it, and it easily could form the basis of a global missile defense.

Critics point to interceptor tests that failed to destroy "enemy" missiles. Conveniently overlooked are the successes: Of the 10 missile defense tests since March 1999, eight were successes. An 80 percent success rate suggests we're doing something right.

Another reason missile defense gets a bum rap is the half-hearted support President Clinton gave it while he was in office. His insistence on abiding by the now-defunct 1972 Anti-Ballistic Missile Treaty (which prohibited a national missile defense) stalled U.S. research efforts during most of the 1990s. In effect, we were trying to get the job done with our hands tied.

Presidential leadership is the key here. Just think what would have happened to NASA's Apollo program without the unqualified support of Presidents Kennedy, Johnson and Nixon. Forget about asteroids-we'd probably still be trying to land on the moon.

Now more than ever, the United States needs a missile defense. As my colleague Baker Spring notes in our book, "Priorities for the President," the United States would be helpless if Iran, Iraq or North Korea (all of which have robust missile programs) lobs just one missile over the ocean toward a U.S. city.

If any nation can create a missile defense, we can. American technology has split atoms. It has launched men into space and put them on the moon. It has created supercomputers that are smaller than a wristwatch, and it can probe the reaches of outer space.

And still some say we can't hit a missile with a missile. Sounds to me like they're the ones with the fantasies.

Edwin Feulner is president of The Heritage Foundation (www.heritage.org), a Washington-based public policy research institute.