It's an alluring idea: If the United States disarms or restrains its military forces, other countries would do the same. The notion is gaining ground in the Obama administration; it needs very careful scrutiny.

The president's thinking about nuclear disarmament is grounded in this idea. In laying out his vision of a nuclear-weapons-free world, Mr. Obama asserted that "as the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act. We cannot succeed in this endeavor [to rid the world of nuclear weapons] alone, but we can lead it."

Let's ignore the question of whether a nuclear-free world is achievable. The president clearly sees America's nuclear arsenal as a central part of the problem. He puts America squarely in the nuclear disarmament dock and offers unilateral restraint as a measure of leadership. Clearly, he believes that unilateral restraint is necessary to get the ball rolling toward universal nuclear disarmament. Put simply, by disarming ourselves, we remove at least one reason for others to have them in the first place.

Those holding this worldview are usually, at the very least, ambivalent about America's military superiority. Mr. Obama doesn't say so, but many of his more liberal followers think our huge lead in weapons technology forces others to try to catch up by acquiring more weapons. Thus, the logic goes, if we want others to disarm, we must do so ourselves.

defense Secretary Robert M. Gates is certainly is no fan of this kind of disarmament thinking, and yet he has a strange ambivalence about aspects of our military superiority. Some critics have charged that his most recent defense budget will erode our military superiority in vital areas.

In justifying his budget, Mr. Gates has said that "every defense dollar spent to ... run up the score in a capability where the United States is already dominant is a dollar not available to take care of our people, reset the force, win the wars we are in." The assumption seems to be that we can afford to narrow the overall defense gap without adverse consequences, because we have "run up the score" and there is supposedly no inherent benefit from a large degree of military superiority over our adversaries.

But Mr. Gates and Mr. Obama misunderstand the real-world dynamics of U.S. military superiority. America's military strength and determination to excel more often than not have discouraged aggression and - in cases like Libya - actually encouraged disarmament. Moreover, other countries don't always mirror our restraint. In fact, seeing the military gap closing can entice them to work harder to catch up, and this could happen faster than Mr. Gates imagines.

A recent nuclear arms race "game" conducted by my colleague, Baker Spring, shows how simplistic arms race ideas can be wrong.

Mr. Spring, a research fellow in national security policy at the Heritage Foundation, brought together experts to simulate real world reactions by nuclear powers to various crises and arms control proposals. In most cases, instead of responding in kind to U.S. unilateral acts of restraint, a majority of states, including Russia, maximized their nuclear forces to the extent their resources permitted. Three of the seven put their nuclear forces on alert in response to the U.S. "de-alerting" its forces. This so alarmed our allies, who feared we were backing off their defense, that they began taking defense measures on their own that escalated the crisis.

Even worse, when the U.S. tried to reassure other nuclear powers by making our nuclear command-and-control activities more transparent, four countries did the opposite, "shrouding" their plans and decisions.

Odd behavior? Not really: Some countries see nuclear weapons as instruments to achieve advantage over others. They aren't nuclear powers simply because we are, and their behavior is dictated not by fear of us, but rather by a desire to achieve some gain over an adversary. Saddam Hussein bluffed about his nuclear weapons program because he wanted to deter Iran, not us.

Unilateral restraint does not always produce the desired response from others. It can backfire and embolden other powers to take advantage of a perceived opening. When other nuclear powers think the U.S. is serious and capable of defense and retaliation, they are far more likely to behave responsibly and in a stabilizing fashion. America's nuclear superiority is not a provocation, as some think, but a deterrent to aggression.

The same is true with respect to America's conventional military superiority. In the real world, the wider the gap over potential adversaries, the less incentive they have to try to catch up. Our superiority is a form of deterrence; it deters enemies not only from challenging us on the battlefield, but from having much hope of ever catching up with the quality and quantity of our weapons systems. We saw this with the Soviet Union in light of President Reagan's defense spending boost.

Conversely, were the superiority gap to shrink and catching up appear to be more attainable, our adversaries would likely accelerate their weapons programs. Allowing our superiority to wane gives an incentive for others to build weapons - providing an impetus for an arms race.

The lessons are clear: Don't assume others will mirror our restraint on military arms, and don't assume we can tolerate marginal erosions of superiority in any category of military weapons. The best way to deter adversaries is to keep our defense as strong as possible, and to demonstrate our commitment to use it if challenged.

Kim Holmes is vice president of foreign- and defense-policy studies at the Heritage Foundation.