There are some things that are worse than a weak economy, and the possibility of a nuclear attack against America's homeland, its forward-deployed forces or its allies is one of those things.

The number of countries possessing nuclear warheads and the ballistic missiles needed to deliver them quickly against distant targets is growing. As that worrisome trend unfolds, U.S. policymakers have to seriously consider the possibility that nuclear deterrence will fail.

It was precisely that concern that led the Clinton administration to increase funding for both national and theater missile defenses in 1998.

The Bush administration stayed on the course established in the Clinton years, spending a relatively modest amount of money -- about 1 percent of the military budget -- on defenses capable of countering a small strategic missile attack. Bush also funded a variety of systems for protecting deployed forces against shorter-range ballistic missiles.

None of these programs threatens the effectiveness of the Russian or Chinese deterrent force. They can only cope with the lesser nuclear challenges posed by countries such as North Korea and Iran, or an accidental launch of a few long-range missiles. Countries with large nuclear arsenals can easily overwhelm them.

Most experts believe it is the smaller arsenals that pose the greater danger today, because the countries possessing them are less stable and less predictable in their behavior.

Even if that were not the case, the absence of effective defenses against small attacks employing ballistic missiles increases the incentives for additional countries to acquire such weapons. Thus, a strong case can be made that building modest missile defenses strengthens deterrence and discourages nuclear proliferation.

But that is only true when the defenses are actually capable of destroying attacking missiles, and boost-phase systems are more likely to achieve that goal. At the very least, they reduce the challenge faced by other defenders by thinning out an attack before each missile becomes a cloud of warheads, decoys, countermeasures and debris.

The new Obama administration can keep this promise alive for a small amount of money. The resources required to sustain all of the boost-phase interception concepts currently funded by the Missile Defense Agency are much less than the federal government spends each day. In round numbers it is $3 billion to $4 billion per year, which is not much money compared with the consequences of even one nuclear weapon reaching American soil.

The three programs that offer the most potential for effective boost-phase or ascent-phase interception of ballistic missiles are:

-- The Kinetic Energy Interceptor

-- The Airborne Laser

-- The Network Centric Airborne Defense Element

(Part 14: Assessing other potential BMD programs)

(Loren B. Thompson is chief executive officer of the Lexington Institute, an Arlington, Va.-based think tank that supports democracy and the free market.)

(United Press International's "Outside View" commentaries are written by outside contributors who specialize in a variety of important issues. The views expressed do not necessarily reflect those of United Press International. In the interests of creating an open forum, original submissions are invited.)