If you shudder at the recurring nightmare of the Washington springtime tourist -- The Thing That Walked Four Abreast -- but can't escape town, there is an answer:

Forget the sidewalk. Slip into the alley.

Washington is gridded with alleys; nearly every block has one, even the far-flung, rolling residential neighborhoods of upper Northwest and far Southeast. And though they are not as lively as they were 40 years ago, when many of the city's poor lived in them, they are by no means deserted.

There is wonderful junk for unashamed adventurers and starving artists, and a chance to study neighbors' backyards, which are infinitely more revealing than their front-porch public faces. And here and there commerce raises its lovely head.

Probably the best-known local backstreet business is BLUES ALLEY, two ex-garages at the rear of 1073 Wisconsin Avenue NW where big-name jazz nowadays costs $10 to $12 a seat. Sam Levy, the Georgetown real estate broker who 18 years ago rented the place for $200 a month to original owner (and Dixieland bandleader) Tommy Gwaltney, says he first mentioned the property to Gwaltney as a joke; a tire dealer was using it for storage. "Tommy took one look and said, 'This would be great.' I thought he was kidding." He wasn't. 337-4141.

DeSales Row, the mostly sunny alley amid 18th, 19th, L and M Streets NW, is the home of two hideaways -- MISTER DAY'S (296- 4448) and E.J. O'REILLY'S PUB (872-1114) -- held apart by a blueprint maker and an auto shop. Both taverns are heavy with pinstripes and heels for weekday lunch, and Thursday night in DeSales Row is a good time to find out which hairstyles are in this year at Marymount College. O'Reilly's has a handful of tables outside (one of them in the sun) and Guinness on tap inside. Mister Day's has Stroh's on tap, pinball and video games, and a fast $3.75 roast beef sandwich.

There's an EXXON STATION in the alley running north from Cathedral Avenue just west of Connecticut Avenue NW -- a peanut's throw from the National Zoo. Not far from there, on an alley east of Connecticut between Woodley and Calvert, is the door to LORD TELFORD'S PUB, where a draft goes for 90 cents from 3 to 7 weekdays. After 7, the hot dogs are still only $1, but the back door is locked; enter through the Tucson Cantina.

Sandwich? There's a cluster of coffee shops in the shadow of St. Matthew's Cathedral. Three are behind the church, between Rhode Island Avenue and N Street NW, and another -- JIM'S PLACE (785-2299), owned by a fellow nonetheless named Joe Chang -- between M and DeSales. "Faster than MacDonald's," says Chang. Steak and cheese sandwiches. Also in the shadow of St. Matthew's, but accessible only from the arched alley next to 1734 N Street NW is an old carriage house serving Middle Eastern fare called the IRON GATE INN (737-1370).

The most immediately transporting alley in town is not actually in town; it's in Old Town. Ramsey Alley, behind King Street south of Fairfax in Alexandria, is full of cobblestones, shade trees and general tranquility (except for the crane currently tearing down one of the old torpedo factories a block away). And it leads to a discovery called DISCOVERIES (548-9448), two floors of "ancient arts" purchased primarily in another hemisphere by owners Paul Berry and Stephen Collins. Discoveries' fare ranges from Egyptian camel-bone hairpins ($3) to solid-brass Moroccan mugs ($9.50) to $175 hand-carved African chairs that are more comfortable than they look. Owner Berry, who wishes the city would give Ramsey Alley a few lights and some regular cleaning, is still friendly enough. "Anybody want to go out there and blow up that crane?" he says. Just kidding.