Congress and the White House are at odds over ways to reduce illegal immigration into the United States. This month, the House of Representatives approved a measure that would tighten security and extend a fence along the 2,000-mile U.S.-Mexican border. President Bush has proposed a guest worker program to regulate what he sees as an unstoppable flow of alien job seekers.

Largely ignored is the need for a foreign policy component. Latin America is the primary source of undocumented migrants entering the United States and, with few exceptions, the conditions that push people out are not getting better. Unless policymakers pay attention, efforts to secure borders and regulate temporary workers could be too little, too late.

To solve them, U.S. lawmakers sometimes find it easier to break big problems into manageable chunks. That's why Republicans in the House of Representatives have for now proposed expanded controls to reduce flow at the borders and punitive measures against employers who hire undocumented workers.

Reducing the flow with technology and stronger law enforcement responds to the majority of citizens' concerns-not just in border states, where more than a half a million aliens transited illegally last year, but also in other parts of the country where undocumented workers seek employment and live in marginal, often crime-ridden neighborhoods.

Few doubt that better, smarter measures are needed to shield the United States against terrorists and transnational criminals while disrupting tourism and trade as little as possible. But even a fence and doubling the number of border agents won't keep out determined migrants seeking to escape starvation back home. They will find other ways.

A guest worker program will direct many toward legal entry points, allow them to come and go, and, by eliminating existing red tape in the employment process, encourage more migrant workers and their American bosses to pay taxes. Moreover, legal guests will toil in the light of day, improving their social integration.

Already U.S. citizens bear the cost of immigration enforcement services provided by the federal government, estimated at about $10 billion in 2002 by the Center for Immigration Studies. These are in addition to state and local expenditures on schools, emergency medical care, and criminal justice not covered by federal programs. Promoting legal employment would offer some relief.

But even stronger borders, better local-state-federal law enforcement coordination, and a user-friendly guest worker program will not stanch the flow if source countries do not implement deep political, economic, and social reforms. With few exceptions, such as Chile, Uruguay, and some islands in the Caribbean, America's hemispheric neighbors to the south are closed societies, plagued by monopolistic practices.

Despite the prevalence of elections and the adoption of some market reforms, Latin America lags behind industrial nations in significant ways. Most of the region's public schools do not educate youth for the modern workplace. Facilities are overcrowded and lack textbooks, and 40 percent of the region's students reportedly never progress beyond grade school. The rural poor-the most likely to emigrate-are least likely to attend at any level.

The Population Reference Bureau claims that by 2025, Latin America's population will rise from 520 million to 702 million. Neither economic growth nor job creation is likely to keep up with the number of new entrants in the labor market. Not surprisingly, Latin America compares to Sub-Saharan Africa in overall crime.

The rise of leftist populism in Venezuela, Bolivia, and even Ecuador has divided citizens and threatens prospects for near-term prosperity in the Andean region by bringing back capricious, personalistic rule and social spending designed to placate the poor without liberating them from the complex regulations, lack of credit, and weak property rights that keep them that way.

Despite improving cooperation in law enforcement, Mexico remains a leading source of undocumented migrants. It is in the middle of a baby boom bubble in which about a million new workers join the labor force each year. Yet, on average, only about 500,000 new jobs have been created in each of the last five years.

President Vicente Fox, the first opposition party president in 71 years of single-party dominance, did much to open Mexico's economy but was thwarted by a divided congress in privatizing sluggish monopolies, improving access to credit, and curbing corruption. Next July, voters might replace him with the populist former Mexico City mayor Andrés Manuel López Obrador, who promises more social spending and a retreat from free markets-a recipe for growing poverty and worker flight.

Mexico is also a transit country for migrants from Central America. Lagging economic reforms in Guatemala, Honduras, and Nicaragua keep new small businesses from flourishing, contributing to high unemployment and crime. In both Mexico and Central America, free trade with the United States helps, but trade is a door that opens only when local governments promote and protect a competitive marketplace.

To alleviate conditions that cause migrants to leave home in the first place, the United States must adopt a serious foreign policy to encourage neighboring states in Latin America to change from "monopoly" to "opportunity" societies. To date, U.S. diplomacy and assistance are largely an amalgam of counternarcotics assistance, trade agreements, and "feel-good" aid programs.

Rather, U.S.-Latin America policy must broadly foster deep democratic reforms that put government and political parties in the hands of constituents instead of charismatic leaders, push for a more open competitive marketplace that helps small businesses to prosper instead of family and state monopolies, and bring about a climate more respectful of individual rights instead of sustaining autocracies where liberties are substituted with entitlements.

Tighter border security and a guest worker program may help the United States reduce the overflow of undocumented migrants pouring over our borders today. But five years from now, U.S policymakers will discover that it was not enough to stem the tide. A focused foreign policy is necessary to help Latin America become more free and competitive.

Stephen Johnson is Senior Policy Analyst for Latin America in the Douglas and Sarah Allison Center for Foreign Policy of the Kathryn and Shelby Cullom Davis Institute for International Studies at The Heritage Foundation.