The immigration debate is in the spotlight again this week as lawmakers are trying to carve out their own distinguishing brand of reform. Proposals range from nearly exclusive law enforcement (Rep. Jim Sensenbrenner) to guest workers with an added citizenship path (Sens. Ted Kennedy and John McCain).

But just as important as which bill will prevail in Congress is the question of what will happen with the roughly 12 million illegal immigrants already in this country. Most likely, they'll stay. The real question is how fast they'll be able to integrate and become Americans.

The status of currently illegal immigrants is a particularly contentious point. Everyone seems to agree that reforming the system is necessary, that a blind eye toward illegal residents erodes the rule of law and that increased border security is a matter of national interest.

But now the sour questions begin. Is a guest worker program necessary? And more importantly, what should happen with those currently living and working in the United States illegally?

On the one hand, as some bills propose, imagine that all illegal aliens are asked to leave the country, although they might be able to apply for a guest worker visa from their home countries. Options include mass deportations and voluntary provisions under which illegal aliens will be required, or have incentives, to come forward and sign up to return home.

The problem with expecting that illegal aliens will just leave is that is doesn't reflect reality. Mark Krikorian of the Center for Immigration Studies reckons that an attrition strategy for reducing the illegal population is possible. But considering that low-skilled immigrants--whether legal or illegal--create substantial economic benefits, and people across the border have powerful incentives to come to the United States, the strategy for downsizing the illegal population by kicking everyone out doesn't look very real.

On the other hand, as some suggest, suppose that a newly created guest worker program allows illegal immigrants to adjust their status--after returning first to their home country or, more realistically, while remaining in the United States. Some are quick to point out that status adjustment will not open the door to permanent residency or citizenship. So the guest worker provision would be a dead end. Illegal immigrants, now with a new guest worker status, won't be able to remain in the United States and at one point will have to return home.

But what some people find so alarming about opening the guest worker door for illegal immigrants is that it might end up leading to a new mass settlement. They're probably right. Since roots have been laid in the new country, and nothing has changed in the old one, the new guest workers will tend to simply settle down, with no motivation to leave. Consider some basic facts: unemployment and low wages will continue to push them out of depressed economies and a myriad of opportunities will keep pulling them into the United States.

If it's true that illegal immigrants are too settled to leave, two things must happen. First, any guest worker program that wants to avoid the settlement cycle all over again needs to be configured so that fresh guest workers have powerful incentives to return home. This entails, for instance, the White House's idea of working with other governments, like Mexico, to make sure that workers receive credit in their home countries' retirement system.

Also, as noted by Stephen Johnson from the Heritage Foundation, the immigration debate has a foreign policy element to it. Free trade agreements and economic reform will improve the conditions in poorer nations, thus minimizing the push factor that sends immigrants out in the first place.

Second, and more importantly, measures have to be taken so that new immigrants are integrated into national life--economically, culturally and politically. A new permanent underclass or non-integrated community would be a catastrophe.

Despite increasing percentages in naturalization, Latin American groups have had a lower naturalization rate than, say, Europeans. Naturalization needs to become both more common and meaningful. The right incentives and policies should help immigrants to learn English and become better educated, which will facilitate assimilation into the adoptive country.

What will happen with 12 million illegal immigrants? If they stay, that's almost the size of San Salvador and Mexico City combined. Though not all, many are likely to stay. A recent report from the National Research Council argues that the education of Spanish speaking immigrants is crucial for the country's economy. Making sure that they become part of America's economic engine, and political future, begins right now.

Jose Enrique Idler is a research fellow at AEI.