If common sense were the coin of the realm, the Senate wouldn’t need the Snowe Rule. It’s not, so it does.

The legislation introduced by Maine’s Sen. Olympia Snowe this week doesn’t sound like much. So obvious, so logical — limit spending in emergency appropriations bills to things that are true emergencies.

But it’s Congress’s habit of ignoring the obvious and defying logic that gets it in trouble with the citizenry and nothing gets the public bile churning like Washington’s tendency to turn one region’s nightmare into Christmas morning everywhere else.

Remember the rock fight last spring over disaster relief? There were exactly two legitimate emergencies in that $8.6 billion bill — $5.4 billion for flood relief in the Midwest and $1.9 billion to continue peacekeeping operations in Bosnia and the Middle East. By the time it got to the Senate floor, the definition of emergency had been expanded to include the way Census 2000 was to be conducted, Cleveland’s desire for a new parking garage and the dilapidated condition of an old movie theater in upstate New York. It took a stalemate, a veto and nightly television images of soggy North Dakotans to finally shed some of the most egregious lard.

The Snowe Rule won’t change the world. Heck, it won’t even change Washington to any significant degree. There will still be plenty of room for Lawrence Welk Museums, mohair subsidies and superfluous Stealth bombers in the regular appropriations process.

But at least that slow-motion exercise is set up for such nonsense. There’s time for debate, time for the pundits to ridicule, time for the public to fume.

Emergency legislation is different. It’s on a fast track, there’s not as much scrutiny, the requirement that new spending be offset with budget cuts to avoid increasing the deficit is waived, as are annual spending caps. Also, senators of conscience naturally are loathe to hold up desparately needed aid to the striken just because some nitwit across the aisle wants to help folks back in the home district pave something.

All of which makes emergency bills an increasingly tempting target for the pork-inclined. And that’s just wrong. As Snowe says: “The Senate created an expedited processs for emergency legislation for very sound reasons, but providing a vehicle for non-emergency items to be rushed through Congress was not one of them.”

The Snowe Rule deserves quick and unanimous approval by the Senate, no parking garages attached.