ANYONE UNLUCKY enough to board a Metro bus full of high school students knows that, collectively or individually, they are capable of simultaneously breaking every transit law, posted or not -- smoking, eating, drinking, radio-playing, and generally making boisterous nuisances of themselves up and down the aisles, secure in the juvenile knowledge that they outnumber the driver. Contrast this with the case of a 25-year-old Department of Labor employee who one day took the subway as well as a lone bite of a turkey sandwich -- and wound up handcuffed and packed off for what she describes as a horrifying and humiliating 31-hour ordeal with authorities in Arlington -- including a strip-search.

The difference on the trains is that an ever-alert force of transit police patrols the cars, not only to protect riders, but to nab anyone who dares to nibble. The moment this woman sank her teeth into the bread, an officer nabbed her. And what happened next? She was escorted unceremoniously from the Blue Line and turned over to Arlington County police.

Her requests for an attorney were denied, she says, and when she refused to answer questions on her own, she was taken to a detention cell, forced to strip "in full view" of male officers, taken to an isolation cell and left there, wearing only underpants, for 15 hours. Eventually, the charge -- "consuming food on a Metrorail car" -- was dropped.

As if this weren't insane enough on its face in every way, the authorities compound the horror by issuing inexcusably cold bureaucratic explanations of the procedures. Metro's reply? "She was warned, you'd better believe it. And once we make the arrest we have no choice but to turn the person over to local authorities. We don't make the laws, we just enforce them. . . . The public appreciates the cleanliness of the cars." Says Arlington Sheriff James A. Gondles: "We don't discriminate on doing strip-searches by the nature of the offense. If it's serious enough to get you committed, you're strip-searched."

Clean subway cars are just grand, and civilized searches of people charged with serious crimes can be justified. But there is no acceptable excuse for submitting anyone to this degrading abuse for taking a bite out of a sandwich on the way to work. Metro's policy-makers, Arlington's sheriff and every other authority who had any responsibility for this awful incident should rescind, remove or otherwise get rid of every pretense on or off their books that could produce anything even resembling this kind of "law enforcement."