NO ONE KNOWS how much Pope John Paul II's week-long U.S. visit will end up costing -- or even how to calculate the cost. But already who picks up the tab has become a subject of considerable unnecessary controversy in three cities. Some religious and civil-liberties groups in Philadelphia and Boston are challenging -- or nit-picking -- proposals by governments in these cities to spend public money on facilities connected with outdoor papal masses; and in New York, local and Roman Catholic officials have been locked in negotiations over who will pay for what.

But by and large, here in Washington and in Chicago and Des Moines, these details are being handled as they should be: without making a separation-of-church-and-state issue out of the logistics. Spending by a city for the smoothest and safest handling of a major event is a legitimate secular municipal function. Even a spokesman for Americans United for Separation of Church and State has agreed that there is nothing wrong with using public money for cleanup, police overtime, police protection and traffic control.

Playing host to world figures and huge turnouts is indeed expensive, as District officials regularly remind us when they are haggling with Congress for more federal help with the bills. Still, here in the capital, whether it is the pope, angry American farmers, anti-war demonstrators or civil-rights marchers, public spending for special services is considered normal and essential. Much of the hair-splitting in other cities over the papal-visit expenses has to do with whether public money should pay for platforms from which the pope will celebrate outdoor masses. That's a long reach for a constitutional controversy, and not worth it.

Far better is the kind of cooperation that separate church and state groups here are demonstrating in their planning. For example, there will be a chainlink fence surrounding the stage and altar from which the pope will say the mass on the Mall and extending to other nearby areas. The police recommended the fence, estimated to cost about $25,000, the church has agreed to pay for the portion around the stage and altar. To help clean up, the church plans to produce hundreds of Scouts on the Monday holiday for volunteer duty. This approach to the visit is a lot more sensible -- and helpful to all taxpayers -- than a drawn-out argument and threats of legal action.