The cause of immigration reform has been red meat to demagogues across the country and last week another helping was served to them by a federal judge from liberal San Francisco. As usual with this overpoliticized issue, appearances were deceiving.

Judge Charles R. Breyer granted a preliminary injunction that, for now, blocks the Bush administration from pursuing a major part of its effort to curb illegal immigration.

In August, the Department of Homeland Security issued a new rule that would have forced employers to fire workers within 90 days if there were discrepancies between their names, Social Security numbers and information kept by the Social Security Administration. The intention -- not a bad one -- was to unmask illegal immigrants who have used phony information to get jobs.

"What part of 'illegal' does Judge Breyer not understand?" Rep. Brian P. Bilbray, the Republican from California who chairs the House Immigration Reform Caucus, told The New York Times. "Using a Social Security number that does not belong to you is a felony. Judge Breyer is compromising the rule of law that he took an oath to uphold."

Rousing stuff, but a reading of the judge's opinion shows that he understands "illegal." He also understands the meaning of "legal" and the harm that would befall law-abiding workers and employers if the administration had been allowed to proceed with the plan to mail letters to 140,000 employers over the status of 8 million employees. The judge was simply being just.

It might be a different case if the Social Security Administration's records were a flawless source of data. But, as the opinion points out, when the agency discovers discrepancies, they are put in a file that "contains more than 255 million mismatched earnings records and is growing at the rate of 8 to 11 million records per year." Moreover, wrote Judge Breyer, the file "contains information about many U.S. citizens as well as noncitizens."

The judge found that employers would bear a significant cost in trying to comply with the 90-day time frame and many authorized workers probably could not resolve discrepancies in the time allowed. There is "a strong likelihood," he wrote, "that employers may simply fire employees ... even if the employees are actually authorized to work." Those employees would be fair in asking Congress: What part of unfairness don't you understand?

In the end, this is not the Bush administration's failure alone -- Congress has not come together to pass meaningful immigration reform. This suit had the odd couple AFL-CIO and the U.S. Chamber of Commerce listed among the plaintiffs, which points up a larger national consensus that has always existed and could prevail if politicians have the guts to stare the demagogues down.

The essential ingredients of reform are well known: tighten the borders; normalize the legal status of the 12 million illegal immigrants already here (as a practical matter, they can't all be shipped home and it would be a blow to the economy if they were); and, yes, find an efficient way to make sure employers hire only those workers authorized to be in the country.

Judge Breyer put a hold on a piecemeal approach. Congress ought to be spurred to try again for a comprehensive solution, which is the real meat of the issue.