This, says my source, "may be the ultimate foreign-cabdriver-in- Washington story."

Ernest Wittenberg, a public relations executive whose office is around the corner from the White House, "flagged a cab in front of my H Street office headed for an appointment on the Hill.

"I closed the door, called out, 'the Capitol,' and sat back to gather my thoughts for the meeting. The cab took off past Lafayette Park and stopped after two blocks.

"S'help me, the driver turned around and said, 'What is this Capitol?'

"I won't burden you with the painful part about explaining the building with the dome and how to get there. I didn't ask where the driver was from or how long he had been here, but I did ask how long he had been hacking. Two weeks.

"Don't they have an exam in local geography before licensing?"

Yes, they have an exam so tough that even I, a nearly 30-year resident, might flunk. But there have been unconfirmed stories of ringers sneaking in to take the examinations in behalf of totally incompetent newcomers. Hail to the Chief

Among the police departments of the region, we've had a Chief Crooke -- Bernard D. Crooke, the Montgomery County police chief -- for some years, and now we've got a Chief Justice.

Pending the disposition of perjury and obstruction of justice charges against Charles T. Strobel, the Alexandria police chief, Deputy Chief Arlen Justice has become acting chief of the department.

Chief Justice. That, as Warren E. Burger might observe, has a nice ring to it. The Eerie Canal

For quite some time, David Howcroft, who lives in the Palisades area and works in Georgetown, was seething. He wrote Metro Scene a letter complaining of the "truly appalling" state of the currently drained C&O Canal bed at the Wisconsin Avenue bridge: "Tires, pieces of a refrigerator and thousands of beer cans and bottles litter" the scene.

Before the letter reached my desk, Howcroft was on the telephone. He passed by on Monday, and said someone -- presumably a crew from the National Park Service -- had cleaned up the mess. Now, if we can only stop people from using the canal as a dump . . . . Under the Avenue

A longtime news source, reading this column on proposals through the years for underground parking in downtown Washington, suggests that we missed one of the biggies. Syd Kasper of Silver Spring provides a reminder that the original Pennsylvania Avenue redevelopment plan, produced by a presidential commission in 1964, called for providing as many as 10,000 subterranean spaces between the White House and Capitol Hill. That part of the plan was scuttled, however, when pressure built up to abandon major freeway projects in favor of a subway.