There's a difference between having an "open door" policy and having no doors at all.

The U.S. economy has been strengthened perpetually via its open doors. Free flows of immigration, trade and capital have fueled the wealthiest economy in history. But the continued success of this policy hinges on us knowing who is attempting to come through those doors -- that is, on fostering community as well as growth.

Today America's exceptional status as a nation of immi­grants is being challenged by globalization, a phenomenon that makes both migration and terrorism much easier. The favored approach of recent years -- a policy of benign neglect regarding the immigration problem -- is no longer tenable.

Successful immigration reform must be comprehensive. A lopsided, ideological approach is bound to fail, whether it focuses exclusively on border security while ignoring migrant workers or vice versa.

Just think through the numbers. Illegal immigration has reached mas­sive proportions. The U.S. currently hosts more than 10 million undocumented aliens. When three out of every 100 people in America are undocumented (or docu­mented with faked papers), we have a profound security problem.

And that's the point Congress should focus on. The real problem presented by illegal immigration is security, not a supposed threat to the economy.

Today the percentage of Americans who are foreign-born (12 percent) is the highest in decades. At the same time, the economy is strong, with higher total gross domestic product, higher GDP per person, higher productivity per worker and more Americans working than ever before. Immigration may not have caused this economic boom, but it is folly to blame immigrants for hurt­ing the economy at a time when the economy simply isn't hurting.

Ironically, efforts to curtail the economic influx of migrants actually worsen the security dilemma by driving many migrant workers further underground, thereby encouraging the culture of illegality.

The real problem with accommodating a flood of undocumented workers is that it makes flouting the law the norm. And that makes the job of terrorists and drug traffickers infinitely easier. To solve that problem, we must develop a nationwide system that identifies all foreigners present within the U.S. A non-citizen guest-worker program is critical and would involve three steps.

First, all guest workers should be iden­tified biometrically. A nation­wide system of identification, such as fingerprints and retina scans, already has been developed for the US-VISIT pro­gram.

A sister "WORKER-VISIT" program is essential for enforcement efforts and would help American companies. Employers who want to hire guest workers would be required to verify electronically that the particular worker has registered with WORKER-VISIT and is eligible to work in the United States.

Second, a guest-worker program must not be amnesty. Potential guest workers should apply from outside the U.S. and be required to have a sponsoring employer. Documented migrant workers would enter with a new status: not citizen, not illegal, but rather temporary worker.

And third, the guest-worker program shouldn't be used as an excuse to create another large fed­eral bureaucracy. Government should never microman­age migrant labor -- or any labor, for that matter. Instead, the private sector ought to run the guest-worker visa pro­cess.

Incentives for employers and workers to comply should be written into the law, along with strict penalties for non-compliance. Guest-worker status should not be a path to citizenship or convey rights to U.S. social benefits. The guiding rule: Treat migrant workers with neither preference nor prejudice.

This century of globalization will see America either descend into timid isolation or affirm its openness. We can't afford to wait. Already China's economic power is ascending with openness, while western Europe declines into isolation.

Too many voices are saying that immigration reform is politically untenable. That supposes a false choice between openness and law. And it misreads the populist demand for a simple solution that's both obvious and true to our American heritage.

Tim Kane, Ph.D., and Kirk Johnson, Ph.D., are economists in the Center for Data Analysis at The Heritage Foundation.