SOMEDAY when Congress gets around to rewriting the presidential campaign finance law, one provision that will surely be changed is the one setting limits on spending in each state. In the meantime, the campaigns vie to see who can most ingeniously avoid the limits -- an exercise that may undermine the legitimacy of a law that otherwise works fairly well.

The original idea behind state limits was appealing. If you're going to limit overall spending so as to give serious campaigns a roughly equal chance nationally, why not also limit spending in each state? So a population-based formula was made that limits spending in Iowa, for example, to $760,000. The problem is that in presidential races not all states are equal. The early retail politics states like Iowa naturally attract more candidate time and spending, and there's a premium on pumping as much money in as possible. So the campaigns try to figure out how to spend money in ways that will help them in Iowa but won't count against their Iowa limits.

One way is to count some of your media expenditures against your limit in other states. Roughly half the time you buy on a Davenport station, for example, is charged against your Illinois limit, under a sensible enough formula adopted by the Federal Election Commission. Also, rental cars are counted against the limit of the state where they're rented -- a bonanza for the Moline, Ill., agencies, where dozens of cars are rented by campaigns and driven across the line into Iowa. Then there's the four-day rule. It wouldn't be fair to count the salaries of national staffers against one state's limit, so the rule is that a salary is not counted unless a staffer spends five consecutive nights in the state. So Bush coordinator Rich Bond, running the Iowa campaign since October, spends every fifth night in Omaha, Neb.

If all this strikes you as ridiculous, you're not alone. The FEC thinks the state limits should be abolished. Officials of Common Cause, which suggested them in the first place, agree. Most candidates readily concur. Exceptions might be some of the more lightly financed campaigns, which have money enough to meet the Iowa and New Hampshire limits but might be vastly outspent if the limits were off. But the limit on total national spending, if strenuously enforced, would still exert a downward discipline on early state spending. The real danger is that the law will be flouted by a desperate campaign willing to chance the chastisement that comes months later when the FEC finds that a state spending limit was exceeded. To prevent the most unscrupulous campaign from getting an advantage, the FEC must vigorously and speedily enforce this not very sensible provision of the law -- until Congress gets the good sense to repeal it.