CHICAGO -- While George W. Bush and other world leaders fret over the proliferation of weapons of mass destruction, former Costa Rican President and Nobel Prize Laureate Oscar Arias Sanchez travels the globe, talking to heads of state about the proliferation of small arms, which are currently far more deadly. "How," he asked during a recent speech to small-arms-control activists, "could killing many people little by little, day by day, be less objectionable than killing many in a single day?"

Sanchez delivered his speech here earlier this month as the keynote speaker at a Northwestern University School of Law conference on the international small-arms trade. The event drew dozens of activists, doctors, public-health workers and lawyers, most of them members of the movement calling for an international treaty on small arms that would place uniform controls on the flow of such weapons among countries.

A small arm is basically defined as a weapon that can be operated by one person -- anything from a six-shooter pistol to a shoulder-fired rocket. Experts at the conference estimated that there are 640 million small arms in circulation, one for every 10 people on the planet. A full two-thirds of these are in the hands of civilians, and each year such weapons kill approximately 500,000 people. (To put that number in perspective, consider that land mines kill 15,000 to 20,000 people annually.) Millions of small arms are produced and purchased every year, making it nearly impossible to reduce the global supply through confiscation and destruction.

Addressing the conference, Lora Lumpe, the founder of the Arms Sales Monitoring Project of the Federation of American Scientists and an expert on the small-arms trade, said that small-arms transactions fall into three general categories. The first consists of legal weapons transfers, which are made by governments themselves or by private businesses or individuals with government approval. Then there are "gray market" transfers, in which government intelligence services covertly ship small arms to states or insurgents. (Lumpe noted that this was a pillar of U.S. foreign policy during the 1980s, when the CIA ran guns to the Nicaraguan Contras, the Angolan UNITA rebels and the mujahideen in Afghanistan.) Finally, there are outright black-market transfers, in which dealers use payoffs and subterfuge to funnel weapons into officially embargoed countries and criminal syndicates.

Though many of the world's small arms end up in the hands of warlords, drug cartels and terrorists, 80 percent to 90 percent of illegal small arms begin their lives as parts of legal shipments. "Governments consider any sale of weapons they make to be, de facto, a legal sale," Lumpe told the conference. This makes it difficult to limit arms shipments to nefarious regimes or violent insurgents.

Many countries, including the United States -- which, if you combine official shipments by the government and private exports by manufacturers, is the world's largest small-arms exporter -- have fairly strict export controls, but according to Lumpe, they are routinely ignored and rarely enforced. And even if they were, she pointed out, the arms trade has become so globalized that controls are easily evaded by routing shipments through countries with lax standards and past officials who are easy to bribe.

As guns flow from the producers in the global north to consumers in the global south, prices are plummeting and access is skyrocketing. "They say that in Nairobi, an assault rifle used to cost something like 60 heads of cattle," Lumpe told me at the conference, "and now it's one chicken."

Having a population that's armed to the teeth generally does not bring stability to developing countries, making peace and security nearly impossible to achieve, even after cease-fires have been successfully negotiated. "What we've seen time and again is that after the peace, when the organized fighting is over, then comes the crime wave if you don't get rid of the guns," said Rebecca Peters, director of the International Action Network on Small Arms (IANSA), in addressing the conference. "You have a lot of young men who used to be soldiers with no job and a gun, and so crime is the natural occupation for those who used to be fighting a war."

Despite the high human toll that small arms take and the obstacles they represent to development, governments are reluctant to impose the kind of transparency on gun shipments that many nations, led by the United States, now want to require for financial transactions. "There's all sorts of reasons that governments don't want to be transparent about what they're doing," Lumpe told the conference. "It's a hallmark of the illegal gun trade that the middlemen who are running the deals have had contact with intelligence agents. . . . This is one thing that stops governments from going after the gunrunners: They know where the bodies are buried."

One would think that the war on terrorism would spur the Bush administration to crack down on the small-arms trade, as such weapons often end up in the hands of terrorists. Unfortunately, the war seems to have had the opposite effect. A recent report issued by a group called Control Arms -- a joint effort of IANSA, Amnesty International and Oxfam -- stated that many governments have actually loosened controls on arms exports to countries that are allies in the war on terrorism. Wendy Cukier, a professor at Ryerson University in Toronto who has published numerous articles on gun violence, said there has been a "dramatic uptick in the client list of countries who are receiving small arms."

At a United Nations conference on small arms in 2001, Undersecretary of State John Bolton defended U.S. policy in this area, saying that the "transfer of all military articles of U.S. origin are subject to extremely rigorous procedures." Bolton paid lip service to the importance of reducing the international trade in light weapons and military small arms -- a category that does not include firearms, which are by far the most common and deadly kind of small weapon. But he also made it clear that the administration would oppose any effort to restrict legal trade and manufacturing of weapons, as well as any mandatory review of how the conference's recommendations were being implemented.

Despite the Bush administration's unsympathetic stance, Peters says that small-arms activists have taken encouragement from the success of the International Campaign to Ban Landmines (ICBL) -- though she's also quite aware that her movement faces some challenges that the ICBL did not. "For one thing," she told me, "there's no National Landmine Association, and there is a National Rifle Association." (The NRA has recently stepped into the global arena and has been lobbying strenuously against a small-arms treaty.)

Perhaps the biggest challenge for Peters and her allies is that attacking the supply of small arms won't necessarily make much of a dent as long as demand for the weapons remains so high. The failed U.S. drug war shows how a supply-side approach to combating undesirable products can lead to a balloon problem: If governments squeeze production in one spot, it pops up in another.

But at the conference, Cukier noted that "with guns there's not a simple dichotomy between supply and demand. Weapons breed fear, breed demand for more weapons, breed fear and so on." Lumpe also recognizes the limits of supply reduction, but she points out that whereas drugs are generally trafficked without state help (there are some exceptions, of course), guns are nearly always trafficked, at least initially, under the direct auspices of governments or with their explicit or tacit approval. In this way, state actors have a great deal more influence over the trade in small arms than they do over the trade in illegal drugs. "If there are two words at the center of this, they are 'political will,'" said Doug Cassel who runs the Center for International Human Rights at Northwestern's law school. "There is a tremendous capacity on the part of the international community to reduce the sale and trafficking of small arms if they want to."

The United States should want to. In recent weeks, small arms have brought down several U.S. helicopters in Iraq, killing dozens of soldiers. Given the historically unprecedented military strength of the American armed forces, it doesn't make a whole lot of sense to be flooding the world with weapons that could someday be used in guerilla warfare -- arguably the only kind of war that an enemy can successfully wage against the U.S. military.

Even if the United States were to carefully restrict all small-arms shipments to regimes with good human-rights records, it couldn't necessarily guarantee that those guns would stay in a particular regime's hands -- or that they wouldn't outlive the friendly regime altogether. Guns have long lives (Lumpe told me that there are still guns from World War II in circulation), and governments, particularly in the developing world, don't. When a new regime comes to power, it often inherits the arms of the old regime, and that often spells trouble for both the citizens of the country and for neighboring states. In his keynote speech at the conference, Sanchez cited Afghanistan as a perfect example of this phenomenon. "No sale of weapons is ever completely safe," he said, "as yesterday's allies become today's terrorists."