One wonders how many hundreds, even thousands, of Metro train passengers have been utterly confused for nearly two years by a map on the concourse of the Friendship Heights subway station.

The map, which apparently has been in place since the station opened for service on Aug. 25, 1984, is one of those neighborhood locators -- the kind that has an arrow that points to the station, asserting, "You are here." Concentric rings indicate how long it takes to walk to nearby destinations.

Just one problem: The map indicates that the passenger in search of accurate directions is at the Tenleytown station, a mile or so down the line on Wisconsin Avenue. (And even the Tenleytown station name on the map is depicted incorrectly; it is labeled Tenley Circle, a name that was changed long before the line was opened.)

While we're at it, one also wonders how Metro's Friendship Heights station attendants, who occupy a kiosk facing the erroneous map barely a dozen feet away, apparently managed to ignore or fail to report the wrong map in all these 21 months. This isn't the first time such a thing has happened. Metro Scene reported last year on a similar map mix-up at Rosslyn station in Arlington County, which prompted Metro to straighten out its maps along the Orange Line. Metro Stop Muddle

On a related subject, Metro train operators approaching Friendship Heights from downtown Washington announce the station as "the first stop in Maryland," irking some District residents who have called this column to voice annoyance. The station straddles the Maryland-D.C. line with entrances in both jurisdictions, so shouldn't it be announced on outbound trains as "the last stop in the District and the first in Maryland," or some variant? The boundary-straddling Takoma Park station, on another leg of the Red Line, should be similarly announced. Hard-to-Get Books

The Quill and Brush, a used-book store on Old Georgetown Road in downtown Bethesda, has in its window a large sign that proclaims its specialties: "Rare, Out of Print and Non-Existent Books."

Nonexistent books? They'd have trouble selling me one.

But the sign's no blunder, says Rick Peabody, a store employe. "That comes from an old New Yorker magazine cartoon," he explained. "A lot of people come in and say, 'huh?' It's an attention-getter."

It works. Never on Weekends

A number of District streets with reversible rush-hour lanes have neon signs that flash on during certain hours, indicating "One Way" and "No Left or Right Turn" to warn the unwary.

But sometimes the timers that run those flashing signs get out of sync with the clock.

So it was yesterday, about 1 p.m., when the flashing signs indicated that 15th Street NW between I Street and Massachusetts Avenue was one way northbound and that intersecting traffic was barred from making conflicting turns. The restrictions ordinarily apply from 4 to 6:30 p.m. Monday through Friday, but never on weekends.

Did the motorists pay attention to the discombobulated instruction? Not at all. They ignored it, just like the Metro attendants did with the sign at Friendship Heights.