IT'S SATURDAY MORNING in Adams Morgan and the sidewalks are full.

Of furniture. People sidestep sofas and mirrors lining 18th Street. Overstuffed chairs, oak dressers, glass book cases, veneered coffee tables, vinyl couches and rollaway beds have been hauled out by hawkers hoping to move them off the sidewalk and into someone's car.

Franc Brown, owner of Yesterday's Nice Stuff, stands in front of his shop wearing a green apron and looking like he should be selling produce instead of furniture. A woman standing next to him is concentrating on a round mahogany table on the sidewalk.

"I can hold it for you," Brown says. "But it's gonna sell today." There's a pause. The woman studies the table. "Should we go inside and write up the receipt?" Brown asks.

The mahogany table (1940s), with two leaves, is sold. The price: $76.

Adams Morgan, particularly the 18th Street strip in the few blocks below Columbia Road, is not a place for the discriminating period antique collector. There's lots of old furniture, there's funky stuff and there's junky stuff, there's some Art Deco and some Art Nouveau. There's even some vintage Dick Van Dyke Show and some early Pee Wee Herman. Most of the Serious Furniture is from the 1920s to 1960s, with a few exceptions. But there's plenty of unusual, different and offbeat pieces, and a fair amount of glass and costume jewelry.

So, you may not find a fine antique in Adams Morgan -- but you will find a neighborhood with a lot of character and a festival atmosphere. Go there to wander, to explore. And if you get tired of looking for a great furniture deal, you can always have a good time just eating a gyro or picking at a plate of Ethiopian food. The thing to remember is that each shop offers its own treasure (some well hidden), be it a beaver hat, a brass door knob or a big Victorian bed.

Here's a tour of the block:

SHIRLEY MASON LIPP ANTIQUES -- 2102 18th St. NW. 234-0030. "I'm so eclectic," says owner Shirley Mason Lipp. "I have Christmas tree tops that sell for $1 and I have things that go for $500, $600." At the moment, Lipp's lot is mostly tree tops and candy dishes, with a few old pictures, plates and some larger pieces.

"This is an urban area," says Lipp. "In the subruban areas, they're more interested in Country. In this area, Art Deco and collectibles are very important."

YESTERDAY'S NICE STUFF -- 20121/2 18th St. NW. 234-2208. Franc Brown has been on the block for about a year. He has lower prices and more simple, sturdy pieces than most of the other vendors on the street. A yellow gateleg table is $53; an oak wardrobe, $123. "I'm still here, so something must be going right," he says.

RUFF & READY -- 2220 18th St. NW. 462-4541. Paolo Narduzzi, founder of Ruff & Ready, used to do two flea markets a week. Once, he says, he remembers shoveling snow out of a parking lot so that he could set up his stand. "I discovered very quickly that a shop was more advantageous," he says. He found a place on 18th Street, in 1980. He has since moved three times on the street. Now his store has taken over two addresses with two floors of furniture, including armoires ($325), vanities ($350), Hoosier cupboards ($425) and less expensive pieces. There are lamps, tables, a perambulator and some stuffed animals heads.

"We have all kinds of fanciful items," says manager Ken Ceccucci. "Our stock is affordable used furniture, and sometimes you'll find an antique. Anybody can walk in here and find almost anything."

MELINDA'S ANTIQUES -- 2222 18th St. NW. 797-7484. An old cassette tape player is blaring Dire Straits. Outside a coat rack holds colorful hats and scarves that blow in the breeze. Melinda ("I just go by Melinda") sits on top of a table inside the shop.

"That piece," she says with a wave toward the back wall, "is $1,200." It's a monstrous dark wood Victorian secretary or vanity. Or something. "And that little thing out there is $1.50," she says referring to a small paper parasol a customer has asked about. "I don't specialize. I appreciate craftsmanship."

A sampling of her wares includes a tea set, a set of martini glasses, some necklaces and a porch swing. She also has a dresser ($75) and a mahogany drop leaf table ($145).

CHENONCEAU ANTIQUES -- 2314 18th St. NW. 667-1651. With a more country look and feel to his store, owner John A. Davis comes closer to offering older, more authentic "antiques" than anyone else on the block. Quilts, one with an authentic front (but new back), are draped over old trunks, one a very large painted blanket chest. The quilts are in the $300 range and the trunks can be more than $1,000.

HOMEWORKS -- 2333 18th St. NW. 483-1897. Here the '30s, '40s and '50s fill the room. "This seems to be the neighborhood where people appreciate what we're trying to do," says Nicole Cohen, who owns the deco haven with her husband, Lee. They've been open for almost two years. "We're selling to yuppies, lots of yuppies," she says, "and a fair amount of gay people." Mostly "under 40."

THE BRASS KNOB -- 2309 18th St. NW. 332-3370. Pieces of buildings fill this shop that should not be missed, no matter what your interest. There are doors stacked up (one with stained glass was priced at $695, a wooden one for $50), door plates ($25) and door knobs (glass knobs sell for about $6.50, brass for about $25). Lighting fixtures from plain to fancy hang from the ceiling, mantlepieces rest against the walls and old tiles are kept in sliding trays. On a Saturday, you elbow around the pieces, as browsers and buyers provide a constant stream of clientele.

"People have traditionally been afraid because this was a dangerous neighborhood," says Donetta George, who owns the shop with Ron Allan. "Now we have a lot of people coming in from the suburbs."