Atmosphere: Old clothes, roll-up your sleeves restaurant. Not for faint of heart or appetite.

Price range: $2.75 to $5.25 for complete dinners and $8 to $15 for a dozen crabs, depending upon size (small to jumbo), or all-you-can-eat crab feasts from $8.50 up, also depending on size of crabs. Carry-out prices slightly lower.

Hours: Open seven days a week but hours vary, usually noon to midnight on weekends and 2 p.m. to midnight weekdays. Crab feasts (all-you-can-eat prices) daily from 5 p.m. to 10 p.m.

Special facilities: Parking on nearby streets; easy access for wheelchairs.

Reservations: First come, first served.

Credit Cards; Cash only but credit cards soon may be accepted.

If you enjoyed the Rabelasian feasting scene from the movie "Tom Jones," then you'll love Ernie's Original Crab House in Alexandria.

Young children have a glorious time smashing crabs with wooden hammers and then picking at the pieces - at least children who aren't squeamish. Amorous couples sit sucking claws and feelers and licking buttery fingers. Large trays of crabs continuously cascade onto tables. And throughout the room dedicated gourmands sit sprawled in blissful stupor before huge mounds of crab shells, ringed by empty beer pitchers, participants in the daily all-you-can-eat-crab feast.

It's not a nautical setting for a crab house, in the heart of Fairlington Shopping Center next to Lindsay Cadillac. And the interior, in assorted plastics and a few wooden shingles, with large garbage cans dragged among the tables to clear the crab-shells, is at best practicaL. Although the windows, painted with seascapes of seagulls and crabs, do have a childlike finger-painted charm.

But the action is on the tables, where the anvil chorus of pounding hammers drummed steadily during our family's two-hour feast last week. A tray of a dozen medium-sized crabs slithered onto the brown wrapping paper of our table, soon followed by platters of fried oysters, clams and french fries for our two boys who have caught and picked crabs in Louisiana and South Carolina - where these crabs were from - but here chose food that required little effort and left them free to use the pinball machines an djuke box.

"I'm sure that's why they're here," said my wife as she deftly broke off the sandbag (head) and back and removed the deadmen (gills), "to keep kids occupied while their parents eat." I nodded and followed her example, trying not to splatter myself with crab juice.

Great delicious gobs of crab meat appeared miraculously on my fingers. "There's also good meat in all those little compartments," my wife suggested, as she wielded the paring knife like a scalpel - the knives are the only implements supplied, beside the wooden mallets.

My lips burned from the "Old Bay" spices the crbs are steamed in and served with. I searched frantically for the pile of brown paper towels, our napkins, to dry my slippery hands so I could hold my beer glass.

"You don't need the sauce, the crab's are hot enough without it," my wife confided as she saw me gasping and grabbing for the beer. I nodded.

A young woman climbed onto an empty table next to us. Instead of dancing or belting out a sea chanty in honor of crabs, which I thought appropriate enough, in this happy crab and beer hall, she began photographing her friends eating at a nearby table. One friend held a long crab claw between her teeth as the flashbulbs popped. Several other customers also came equipped with cameras to record the crab-eating performances of their friends, though most stood only on chairs to take the pictures.

In June the local soft shell crabs begin arriving from the bay, one of the world's great delicacies, sought out by fish as well as man, and then you don't have to worry about removing the deadmen and sand bag, but just devour the whole thing. Ernie's imports fresh Louisiana and South Carolina hard shell crabs most of the winter but as Chesapeake Bay crabbers there soon will be local crabs, according to our friendly, fast and knowledgeable waitress, Janet.

"It's the best crab I've ever eaten." said our 11-year-old, who cracked and ate one crab just to keep his hand in. "But I really like the atmosphere here . . . you know the juke box and pinball machines."

"The fried oysters were very good," our 14-year-old allowed on one of his occasional visits to our table to ask for more quarters. The $2.25 for songs and games was one of the crucial expenses of the meal, though not listed on the menu or bill.

Our bill was $28.49, excluding tip and pinball.

Crab houses like Ernie's are not for the fastidious or well dressed, but it is a delicious learning experience for young children (jaded teen-agers have pinball and other delights to choose from) and those adults who somehow have gone through life without encountering a crab head on at the table.

There is another Ernie's in Hybla valley near Mount Vernon, on Richmond Highway, which opened about three years ago. "Ernie's Original Crab House" was in Cheverly, Md., for several decades before migrating to Crystal City in the late 1960s: It moved to Fairlington in 1970 when highway construction took the Crystal City place.