Most of the 50 or so shoppers at Reston's Memco store last week knew that it soon would be closing for good. But none was prepared for the announcement that boomed over the store's public address system minutes before its regular closing time:

"Attention Memco shoppers. In 15 minutes this store will be closing its doors. This is it, folks. The end. Everything goes, $25 a level cartload. Go on and fulfill your shopping fantasies."

It was nothing less than a license to loot.

For a moment, the shoppers were stunned. Then there was a frantic rush. First to go were the expensive items: small appliances, guitars, automotive parts. But by the end, even the chipped mugs and other rejects were being thrown pell-mell into shopping carts.

"I can cut the wires off these electric socks," said Sidney Sellman, of Shouse Village, during the confusion. "But where am I going to find a 38-inch-waisted man who wears lavender Izod belts?"

Technically, the Memco going-out-of-business sale had been under way since Jan. 18 when the new owners, Bradlees, a New England department store chain, decided to close the seven Washington area outlets. On that date, the merchandise was discounted 30 percent.

By March 8, closing day, the discount rate had risen to 70 percent.

Some shoppers raced around while others were methodical. One teen-aged girl systematically defoliated the greeting card rack while two friends plundered the entire cosmetics department.

On the final night, a half-hour before the surprise closing announcement, all footgear was selling for 15 cents on the dollar and Ali Shar, a native of India, queued up behind a cartload of children's lace-stitched cowboy boots.

The lot, approximately 40 pairs, cost a grand total of $58. Shar said he was delighted with the purchase, which he planned to ship to India.

With most of the store's space vacant and blocked off, all remaining merchandise had been pushed into the center like water in a vanishing mud puddle. The Muzak drifted over now-ransacked aisles, in which a small boy kicked imaginary goals with plastic clothes hangers.

The consensus among shoppers was that things were pretty well picked over. Still, they continued to search with the slow, circling movements of marauding sharks.

Graham Colley from Broad Run Farms parked himself on a folding chair. His wife, Grace, was seen in the distance scooting around the near-vacant houseware department.

"We've already spent $500," said Colley, indicating three overflowing shopping carts, "and she's not through yet."

Then, at 8:45 p.m., just as salesman Jolly Vasciento rang up purchases behind the jewelry counter, the music cut off and a forceful voice interrupted with the message that created pandemonium.

After the initial rush, depleting what remained of the best, virtually everyone engaged in impulse snatching.

Jammed into the maw of bulging carts were such hot items as cans of hamster cage freshener and tubes of mustache wax. Size didn't matter, or color, or usefulness.

"Hey," called out a man, "can we take the fixtures?"

When the end finally came, the fixtures were still in place. Ceiling lights flickered to warn shoppers it was over. By 9:13 p.m., the doors were locked.

Outside, as station wagons backed up to the loading area, people were busy making spot estimates as to the value of their booty. Best guesses were that the average $25 cartload held more than $700 worth of goods--a cash price that totaled less than what shoppers normally would have paid in Virginia sales tax for the merchandise.

"It was," as one man reflected, "a lot like stealing."