With another test flight scheduled for June, and unqualified backing from the Bush administration, it won't be long before the subject of missile defense comes back onto the national radar screen.

Good thing. Since the late 1960s, foes of ballistic missile defense have successfully blocked the United States from deploying an effective missile-defense system. As a result, our armed forces today cannot stop even one ballistic missile launched at U.S. territory. And we possess only the most limited ability to protect our allies and our troops stationed abroad.

Such vulnerability may not have appeared quite so serious in the Cold War era, when both the United States and the Soviet Union had enough missiles to make a "first strike" seem suicidal. But no longer are we sparring with leaders such as Leonid Brezhnev over ways to cut long-range arsenals. Today's missile threats come from countries long referred to as "rogue states" -- North Korea, Iran, Libya, Syria and others -- who are only too happy to exploit this chink in our national armor.

Indeed, the missile threat to America has grown even since a 1998 congressional commission, chaired by Secretary of Defense Donald Rumsfeld, first warned of this danger to U.S. security. The latest global threat assessment by the National Intelligence Council says the risk of the United States being attacked by a missile carrying chemical, biological or nuclear warheads is greater today than during most of the Cold War.

And U.S. intelligence sources expect it will get worse, with potential terrorist attacks getting "increasingly sophisticated and designed to achieve mass casualties." After all, it's been more than two years since North Korea, a world leader in the export of missiles and weapons technology, fired a three-stage rocket over Japan, and the news since then has brought more reports of missile proliferation. About two months ago, the United States discovered a Chinese firm had sold to Iran equipment critical to the manufacture of ballistic missiles.

Which is why all Americans should appreciate the signals being sent by the Bush administration on this crucial issue. Secretary of State Colin Powell has endorsed missile defense as "an essential part of our overall strategic force posture," and Secretary Rumsfeld has pressed our allies in Europe to join the United States in supporting missile defense.

Here are a couple of additional pointers for the administration:

• Continue to affirm America's decision to deploy a missile-defense system. There's this wrong-headed but persistent notion that the president still has to decide whether we'll deploy a missile defense. But that decision was made over a year and a half ago, when Congress passed and President Clinton signed the National Missile Defense Act of 1999, making it official U.S. policy to build a system "as soon as is technologically possible." What President Bush must do is figure out which system he wants to deploy: land-based, sea-based, space-based, or some combination.
  
  
• Declare the 1972 Anti-Ballistic Missile Treaty null and void. If there's any single reason Americans are unprotected today from missile attack, it's because the United States still clings to the ABM treaty, signed nearly 30 years ago with a country that no longer exists: the Soviet Union. The treaty prohibited the construction of any national missile-defense systems. But with our former treaty partner gone, the agreement is no longer in force. Fortunately, Secretary Rumsfeld seems to understand that our defense needs have shifted dramatically since the Cold War.
  
  
• Lift restrictions on the testing of a sea-based missile defense. Such a system offers several advantages over the land-based system President Clinton had been contemplating. Because sea-based interceptors can be positioned on existing Navy Aegis cruisers, this system would be cheaper to build: $8 billion (a price tag that includes critical space-based sensors), instead of $31 billion. It also would take less time to build, with a targeted deployment date of 2005, rather than 2007. And because it would be based on ships, it would be mobile and cover a far greater area more efficiently than a single site in Alaska.

But the most important thing is to act -- and now. Because the other side is hardly standing still.

Baker Spring is a research fellow in the Davis Institute for International Studies at The Heritage Foundation.