By Tamar Jacoby

The conventional wisdom is all but unanimous, so much so that even those who hold the opposing view pay homage to it. Sure, some people dispute even the notion that we need foreign workers to keep the U.S. economy growing. But among those who recognize the necessity of a continued flow of immigrants to do dirty, unskilled jobs that educated Americans increasingly no longer want to do, the mantra goes unquestioned: What's needed is a guest worker program to deliver this labor in a timely, efficient way.

But the conventional wisdom is wrong, and as the Senate debates immigration in the weeks to come, members would do well to reexamine the assumption. The last thing the United States needs is an inflexible guest worker plan.

It isn't hard to understand where the idea came from or why it's popular in Washington. Policymakers from George W. Bush to Sens. John McCain, John Cornyn and Edward Kennedy grasp that the main problem with our immigration system is the lack of visas for foreign workers. International supply and demand -- demand created by U.S. labor needs -- generate a flow of roughly 1.5 million immigrants a year. But our annual immigration quotas accommodate less than two-thirds of that number, producing an annual spillover of about a half-million illegal workers that erodes the rule of law and undermines our security.

The logical remedy: to provide these additional workers with visas and allow them to enter the country in a lawful, dignified way. The only problem: Policymakers are afraid the public would reject such a large increase in permanent immigration. So even those who have been most courageous in promoting reform talk instead about temporary visas. Bush and Cornyn would require foreigners to go home at the end of their work stints. McCain and Kennedy would allow some workers to stay permanently, but they, too, call their proposal a temporary worker program, and many of those who support their package -- including myself -- have gone along in adopting the term.

The problem with the guest worker idea starts with practicality: Appealing as it sounds to some, a time-limited program will not work. The adage is true: There is nothing more permanent than a temporary worker. Many of those who come to the United States for short stints will want to stay on when their visas expire, perpetuating the underground economy that the program is supposed to eliminate.

This isn't just speculation -- look at the reality today. True enough, many young foreign workers initially come to the United States for what they think will be a short visit, and many do go home after a few years. But unlike past such workers, an increasing number are now staying on. This is partly a result of U.S. policy: Our efforts to fortify the border have made it harder for people to travel back and forth. But other, deeper forces are at work. The traditional flow of migrant farmworkers -- truly seasonal laborers, usually single men -- is giving way to a more diverse stream: both men and women, often with families, less rooted at home and more open to the lure of life in America.

Meanwhile, growing immigrant communities have made settling here a more attractive choice. Of some 11 million illegal immigrants in the United States, only 2.4 million are single men, while nearly half are couples and many have children. Legal migrants are even more rooted.

The bottom line: It won't help to bring our quotas more into line with the size of the immigrant flow if we don't also craft a policy in keeping with the way these workers behave -- and today that means accepting the reality that many will want to settle permanently in the United States.

But that's not all. Admitting foreign workers on a strictly temporary basis would also violate American traditions -- our democratic values and our history as a nation of immigrants -- and it would be deeply unpopular with the voting public.

The Manhattan Institute and the National Immigration Forum recently conducted a series of focus groups testing two contrasting options: a guest worker program or a more traditional immigration plan based on the idea of citizenship. The results ran sharply counter to the expectations of policymakers in Washington. Democrats and Republicans alike overwhelmingly preferred the citizenship model for reasons of both principle and practicality. It might make sense initially, these voters said, to admit workers on a provisional basis. It might also make sense to create incentives for the more transient to go home at the end of their work stints. But if they worked hard, put down roots and invested in their communities, wouldn't we want to encourage them to stay? Don't we want immigrants to assimilate? Don't we want to attract the kind of hard-working, committed folks who plan for the future and invest?

The answer is, of course, that we do. This isn't just the American way, it's also the antidote to many of our worst fears about immigration: Sojourners with no stake in the future are going to be much less likely to learn English or buy their own homes or make an effort to move up on the job.

Sure, a citizenship plan looks like a bigger gamble; like the workers, the changes that come with it will be permanent. But surely it would be better to face up to that change and shape it in a way consistent with our values. Rather than a one-size-fits-all guest worker program, we need a system that leaves room for workers to choose, welcoming those who feel they belong and who work their way up and make our country stronger as they do.