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If you want to send arms-control advocates (search)into a tizzy, just tell them that nuclear weapons in the hands of responsible nations have a stabilizing influence on international relations.

No, really. Mention that nuclear weapons (search) ended World War II, kept the Cold Warcold and likely deterred Saddam Hussein from using chemical or biological weapons in the first Gulf War (search). Then, if they are even one millimeter short of apoplexy, suggest that we need new nukes to keep the peace today.

And all of this is demonstrably true. We regularly modified our nuclear arsenal during the Cold War (search) to reflect our evolving relationship with the Soviet Union. As a result, we kept the Soviets from using such weapons against us. The Soviet Union (search) eventually collapsed when its leaders realized they could not match American firepower or technology.

No such bulwark of deterrence exists today. This is unacceptable, as proliferation is advancing at a dangerous pace. China has begun a nuclear modernization program; India and Pakistan have tested nuclear weapons; nations such as Iran and North Korea have edged closer to becoming nuclear states. And even non-state actors -- terrorists such as Usama bin Laden who command no nation -- can become nuclear players if they can acquire an old Soviet warhead on the black market. And bin Laden's organization -- al Qaeda -- has shown it is willing to inflict mass casualties on U.S. soil.

Strategic deterrence was difficult enough during the Cold War, but it has become nearly impossible today. More states possess nuclear weapons, and many of those nations do not understand each other, nor the international chain reaction a nuclear attack would cause.

What role do nuclear weapons play in this increasingly dangerous world? The Bush administration has asked Congress for $20 million to study this question, but many lawmakers want to limit or eliminate those funds.

The question is too important to be answered on the cheap. The huge arsenal of devastating weapons with which we won the Cold War won't be appropriate for most future conflicts. In many cases, the theaters of conflict are too small, and the enormity of such weapons would lead to more casualties among innocents than combatants. For instance, we couldn't unleash such weapons against either of our last two adversaries -- Afghanistan or Iraq.

In light of this and other factors, the time has come to re-evaluate the role of nuclear weapons in national security policy, especially what experts call "low-yield" nukes (search) -- weapons that can, say, wipe out enemy headquarters buried deep underground, as opposed to ones that can level an entire city. Traditionally, these weapons are meant to counter adversaries with large land forces that could overrun America's expeditionary forces. This requirement endures, but tactical nuclear weapons (search) also may be the best way to address emerging threats.

A tactical nuclear force may deter an adversary from using biological or chemical weapons against American forces in the field. An enemy leader may not fear America's conventional response to the use of such weapons. He may believe his forces could withstand or defeat the United States. Or, he may doubt the United States would retaliate with existing nuclear forces because of our demonstrated reluctance to kill innocent people.

Smaller nuclear weapons -- sized to wipe out hostile forces without extensive damage beyond that -- have proven to be effective deterrents. During the first Gulf War, the first Bush administration purposefully let it be known that any use of chemical or biological weapons by Saddam Hussein could provoke a tactical nuclear response. Saddam, far more capable of deploying such weapons then than in Gulf War II, held off.

Furthermore, the battlefield of the future may require a tactical nuclear response. For example, America's arsenal of information technology has given it unprecedented advantages on the battlefield. It often can wipe out enemy forces before our troops even come within range of the enemy's weapons.

Precision-guided munitions enable U.S. armed forces to target almost anything, anywhere, at any time. America's enemies are adapting to this advantage by placing troops, weapons, command and control, and other combat elements underground. Until conventional weapons and/or forces can be developed to destroy these underground targets, the United States should consider having low-yield tactical nuclear weapons.

America's enemies don't respect our Cold War-era arsenal of nuclear weapons because they doubt we'll unleash those terrible payloads on innocent civilians. And we all know that if a threat isn't credible, it doesn't deter. As a result, we grow more vulnerable to attacks by the day. That's why it's urgent Congress funds the president's research request and that we get moving on the next generation of nuclear weapons.

Jack Spencer is a senior policy analyst for defense and national security in the Davis Institute for International Studies at The Heritage Foundation.