STRICT CONTRIBUTION limits are a central tenet of the federal campaign finance law -- and, consequently, an unceasing focus of efforts to undermine it. The latest such stealth attack is headed to the Senate floor in the form of a seemingly innocuous amendment to an appropriations bill. The provision would change the rules for leadership PACs, the political action committees set up by many lawmakers in addition to their regular campaign committees. Under the current rules, leadership PACs, like ordinary political action committees, can't give more than $15,000 annually to the national political parties. But the provision would remove that limit, letting lawmakers transfer unlimited sums from their PACs to their party.

Why would they want to do that? Because the lawmakers are barred from spending money from these leadership PACs directly on their own campaigns. Transferring the money to their party committees lets them do an end run around this restriction, because the party would then be free to spend those funds on the candidate's behalf. Thus, instead of being limited to raising $2,100 from each individual contributor per election, lawmakers could have their wealthiest supporters give $5,000 more. For a senator seeking reelection, that would mean that an individual could give up to $34,200 -- $5,000 a year plus $2,100 each for a primary and general election.

This ill-advised provision would increase the influence of deep-pocketed donors, make incumbents even less vulnerable and set a dangerous precedent for making fundamental changes in campaign finance law. As Sens. John McCain (R-Ariz.) and Russell Feingold (D-Wis.) explained in a "Dear Colleague" letter this week, the provision would let lawmakers subvert the existing contribution limits -- limits that exist to diminish the risk of corruption. The new loophole, moreover, would be available only to incumbents, because the provision defines a leadership PAC as one operated by a federal officeholder. This is the last change that should be made to a system already tilted in incumbents' favor.

If this kind of substantive change in the campaign finance law is to be made, it shouldn't be done by slipping it into a barely related, must-pass appropriations bill that's apt to come back from a conference committee with even more mischief attached. When the funding bill comes to the floor, senators should support the effort by Mr. McCain and Mr. Feingold to remove this noxious provision.