I HOPE YOU DIDN'T BLAME the guy doing about six miles per hour in the left lane of the Memorial Bridge: The tour-tape narrator on his cassette deck told him to stay in the left lane. But then, his brother and his dad had a brief, loud discussion -- and he didn't catch which way he should veer at the D.C. end of the bridge.

He veered right; he rewound the tape, and discovered he was supposed to go left. Despite his extensive, 11-year experience creeping along local roadways, correction of this error involved a good 10 minutes, a couple of sharp words with Dad, and one less sharp but nonetheless illegal U-turn.

The few portions of the tape that he actually heard were, it seemed, well done and charmingly informative. His sister-in- law, a schoolteacher, at one point said from the back seat: "This is really good." (It was one of the few things anyone said while the tape was running; it was not unlike watching television -- except that it was 3-D, of course, and you could conceivably die.)

Mostly, in any case, he listened only for directions and scenic cues -- alternating between sudden sprints for still- green traffic signals, and foot-tapping, off-road idles (while the narrator elaborated, say, on some lesser-known contents of the Library of Congress).

At the end of side one, the narrator said to "flip me over" and continue with Part Two of the tour. (Part One had, at that point, taken them from Arlington Cemetery through the Mall, around behind the Capitol and back into West Potomac Park.)

Several times, he tried to flip whatsisname over and continue. But the tape would not play. He told his Dad, who owned the car, that this was probably "the stupidest tape player" he had ever encountered. Finally, before anyone could top such high-rent wit, his brother reached over the seat, popped the tape out and peered into it. The tape had broken.

This was last Saturday. The tape was last seen on Ohio Drive near the Tidal Basin -- a few feet from where it was also last heard.

About a quarter-mile down the road, the shifter broke on the car. This did not affect his judgment of tour tapes, of course, as it was entirely unrelated. His brother, in any case, again came to the rescue and fixed the shifter -- otherwise everyone would've had to walk.

Which is, come to think of it, what anyone who uses a tour tape ought to do in the first place. -- Roger Piantadosi.

HEAR YE, SEE YE -- There are two tapes available for Washington tours, both of which limit their descriptions to monuments and buildings along the well-beaten paths within the White House/Lincoln Memorial/U.S. Capitol triangle. They are best if used on foot, with a walkaround tape player of some kind -- or if used as a prelude to actual touring, in the inert safety of one's own home.

The first -- a general-interest production with music, sound effects and actual wit -- is from CCInc./Auto Tape Tours (Box 385, Scarsdale, NY 10583); it was $11.95 at Travel Merchandise Mart on K Street. Though the CCI tape is geared for automobile touring, it's entertaining and informative enough to stand on its own.

The other is a more detailed, architecturally oriented two-tape set from Travelcassettes ($14.95; Box 982 New Haven CT 06504-0982). It is not as entertaining as the CCI tape -- often sounding like someone reading aloud from a textbook -- but it is better suited as a walking-tour aid.