THIS CONGRESS has not been called upon to do much in the way of real governing. By that we mean passing legislation -- such as the Simpson-Mazzoli immigration bill -- that deals fairly and realistically with a matter of great importance to this country's future. Today is probably the last chance for Congress to act on this measure. Thanks to the determined efforts of Rep. Charles Schumer and other conferees on the bill, good compromises have been worked out on numerous controversies of central importance. But conferees have bogged down over an issue that is actually of minor consequence.

The administration is now insisting that the conferees write into the statute a $1 billion-a-year limit on the federal government's liability for welfare and other costs that states might have to pay for illegal immigrants who would attain legal status under the bill. The conferees have already agreed to write such an agreement into the conference report on the bill. But representatives from states with large numbers of illegal immigrants, such as California, Texas and Florida have balked at adding new language to the statute itself.

On the face of it this seems like a substantial disagreement. On the one hand, states with large illegal immigrant populations argue that it isn't fair to burden their taxpayers with costs of a legalization program that, together with tighter controls on future immigration, will offer benefits to the whole country. On the other hand, the White House argues it will be difficult to verify which benefit costs can be attributed to the legalization bill, so that, without a cap, the federal government could incur large liabilities.

In fact, risks to both sides are much exaggerated. Sen. Alan Simpson, who has been dutifully arguing the administration's case in conference, notes that states are alrady benefiting from the taxes paid by illegal workers, so they shouldn't mind sharing in the costs of providing them with services. Even more important is the fact that although illegal immigrants are supposed to be ineligible for most social benefits, many are in fact already receiving them. As a result the added costs are not likely to be large for either the federal government or the states -- and they are even less consequential when you remember that tighter controls on recent and future illegal immigrants will produce substantial savings for all levels of government.

Accepting the cost cap isn't really much of a concession, since, if it proves to be a substantial burden on certain states, Congress could always raise the cap at a future date -- just as it has regularly raised symbolic caps on food stamps and other essential programs. And, for the moment, states can hardly be worse off with the federal government agreeing to pay $1 billion a year for costs that states are already incurring in large part. By insisting on the cost cap, the White House has provided a convenient excuse for each side to walk away from the measure and blame the other for its failure. Congress shouldn't be tempted.