THIS EDITORIAL is for anyone who has ever circled the Mall, looking for a place to park. Or who has been irritated by all the cars that are circling the Mall, looking for a place to park. Or who has breathed fumes of buses that are idling near the Mall, or had a perfect photo ruined by those idling buses. Or who has considered taking the family to the Mall and decided against it, because it would be impossible to park.

Have we left anyone out?

Oh, yes. Anyone who’s been stuck on the Mall looking for a bathroom.

An energetic and civic-minded nonprofit organization called National Coalition to Save the Mall is promoting what sounds like a pretty sensible idea: build parking under the Mall. The facility, which the group suggests might stretch from Ninth to 12th streets NW, would serve a triple purpose, providing on its bottom level cisterns to collect rainwater and groundwater runoff and a reservoir to capture water in the event of major floods. The water could help keep the Mall’s grass green, and the extra capacity could save Constitution Avenue and its buildings from damage in an era of increasingly severe weather.

Officials have recognized the need for such a flood-control facility, but an estimated $400 million cost has put off serious consideration. Over a long period (say, 30 years), parking fees, primarily from buses and out-of-town tourists, could pay for the construction.

And why stop there? Promoters of the idea, who include the philanthropic president of Southern Engineering Corp., Albert H. Small; the architect Arthur Cotton Moore; and coalition chair Judy Scott Feldman, point out that such an underground space could include washrooms for tourists, shower facilities for tour bus drivers and underground connections among the museums and Metro. Fees and parking hours would have to be thought out carefully. But if the internal roads of the Mall could be freed up for pedestrians and cyclists, maybe along with a Circulator bus, the visiting experience would be more pleasant for everyone.

So far the idea is in the early stages, with plenty of financial and engineering challenges no doubt to come. But as always on the Mall, the biggest challenge may be political: So many local, regional and federal agencies have overlapping claims to the territory that it’s hard to get anything done.

The promoters have taken the idea to many of these stakeholders and, so far, have received encouragement. Del. Eleanor Holmes Norton (D-D.C.) told us that a great deal of “due diligence” obviously would be needed but that she liked the coalition’s idea of a public-private partnership and the principle of going underground.

Pedro Ribeiro, spokesman for Mayor Vincent C. Gray (D), told us that the absence of tour-bus parking is a particular problem for managing traffic around the Mall. City officials think the idea is intriguing and worth further exploration, Mr. Ribeiro said.

We think so too.