Immigration reform is like tax reform: Everybody agrees that the present system is unfair, that it encourages lawlessness, and that it must be changed.

But if the national consensus favors a system that is fair, equitable and enforceable, there is hardly any consensus at all as to what fairness entails, or what would constitute an acceptable system of enforcement. And as a result, the prospect of genuine reform in immigration seems as remote as genuine reform of the tax code.

The fundamental problem is that the American economy works like a huge siphon, drawing desperate thousands of job seekers illegally across the Mexican border. The question is whether to try to plug the siphon on the Mexican side (by helping Mexico and other Central American countries to develop their economies); cut it in the middle (by vastly increasing border patrols) or stop it on the U.S. side (by imposing sanctions to make it less likely that the illegals could find work here).

As a practical matter, the first two options are useless. Even with an unaffordably generous amount of U.S. aid for the south-of-the-border economies, the United States would continue to be too attractive to resist. The long border with Mexico makes enforcement at entry essentially impossible. All that's left is some way of removing the temptation for American employers to hire the illegals. And that is where every reform attempt, including the latest effort by Sen. Alan K. Simpson (R-Wyo.), bogs down.

The Senate-side sponsor of the last year's failed Simpson-Mazzoli bill would abandon the criminal sanctions of that proposal in favor of civil penalities against employers who hire illegal aliens: a $5,000 fine for a second offense.

Opponents insist that such a provision would have a devastating effect on all Hispanics -- including American-born citizens and legal immigrants. Rather than risk fines of the sort proposed by Simpson, they say, many employers would simply refuse to hire Hispanic, Hispanic- looking or Spanish-surnamed applicants.

They also object to the fact that the Simpson bill, introduced without House cosponsorship, would eliminate Simpson-Mazzoli's direct connection between employer sanctions and amnesty for long-term illegals. The newest proposal would delay amnesty until a presidential commission certified that the sanctions were actually working to reduce the entry and employment of illegals.

In addition, there is the debate over whether illegal aliens are taking jobs that otherwise would go to unemployed Americans -- particularly minorities. It may be impossible to prove the job- taking effect of 2 million or more illegal immigrants, but it does seem reasonable to suppose that, absent the illegals, not all the employers would go out of business, and those that continued to operate would have to hire somebody.

But there are problems aplenty, even stipulating that no American would go jobless as a result of the employment of workers unlawfully in the country. Already the Supreme Court has ruled that the children of illegal aliens must be educated at public expense. The illegals are also entitled to at least some of the other benefits enacted for American citizens, including public welfare and Social Security. It may be hard-hearted to want to deny such benefits to any poverty-stricken resident of the United States, regardless of legal status. But it seems eminently sensible to want to reduce their influx.

Interestingly, the opponents of virtually every proposal to do something about the influx have failed to propose any practical solution of their own, aside from guest-worker proposals which would "solve" the problem by legalizing the illegals.

It's hard to avoid the suspicion that, no matter how much they claim to favor reform, they really like things pretty much the way they are. Those of us who believe that the present situation is unfair, expensive and a serious threat to the job prospects of low-income Americans had better back the Simpson proposal or come up with something else with a decent chance of success.