IMAGINE IT'S Christmas in McLean. All is quiet at the Civil house. The skeletal remains of an 18-pound turkey lie scattered across the dining room table, mingled with splotches of cranberry sauce and giblet gravy. Mr. Civil, who had a little too much Christmas cheer, is snoozing on the sofa. Mrs. Civil, ready for a little Christmas nap herself, regards the scene with nostalgia in her heart. She approaches little 8-year-old Joey Civil, who is sitting in a corner by the tree, and, smiling warmly, watches him play with his new electronic computer toy.

"Having fun with your new toy, Joey?" she asks in a maternal tone.

Joey doesn't seem to hear.

"Joey? How do you like your new toy?"

Joey, as if awakened from a dream, turns his head slowly. "oh. Hello . . . Mother. Yes . . . this is a completely adequate . . . toy. At the moment . . . I have computed the . . . distance between two warring . . . space orbs . . . In precisely 32 microseconds my phasers . . . beepeep . . . will fire on the . . . beepeep fssszzzhmmm . . . Chronoid sphere . . . It will be demolished . . . instantaneously . . . This is worth . . . hmmmmmmmmmm chungachungachunga . . . 20 points."

The corners of Joey's mouth turn up impishly in mild self-congratulation. He returns to his game. Mrs. Civil's eyes water in approval.

"That's nice."

Although Joey is purely imaginary Christmas kid, he could be playing with any number of this season's hottest toy items. Electronic toys based on the computer chip promise to be more popular than ever -- the selection has grown in quantum leaps since they first appeared two years ago -- and manufacturers are keeping pace with the advancing technology by making them more complicated, more versatile and more demanding.

In other words, it takes an 8-year-old to understand them.

At Woodward and Lothrop's downtown store recently, saleswoman Beatrice Curry reached behind the glass counter and pulled out a "Maniac" game. "Maniac," which has been extensively advertised on television, is the Ideal company's challenger to Milton Bradley's immensely popular "Simon." Both games test players' memory and dexterity by challenging them to recall as quickly as possible varied beeps and tones in number or in precise order.

Curry switched on the machine, watching as it first flashed the number 88, then double-H, then random musical tones. After a brief silence, it scored four 00s.

She looked at the machine in frustration.

"I've been here ever since they brought that thing in and I still can't figure it out," Curry moaned. "First the 88, then the H's then beep, beep, beep. I don't know what it means."

From all outward appearances, most toy stores will seem very much unchanged from last years. Many of the toys popular then have remained. But at the front counter, where the electronic hand-computer-sized gadgets are stored, a quiet revolution is taking place.

This year, Sears is devoting 12 full pages to computer toys. Mattel has introduced new baseball, soccer, hockey and a second and more versatile football game to its lineup. Coleco is selling one that plays astrological games. Even Playskool, long a leader in simple toys for tots and preschoolers, is accompanying its "Alfie" robot, which plays tunes and question-and-answer games, with a "Major Morgan the Electronic Organ," a calculator that permits children to create music by matching colors and numbers; and "Star Rider," a computerized fantasy machine with rocket booster sounds, flashing lights and laser weapons.

"Star Rider," said Playskool public relations officer Margene Lehman, "gives the child a chance to be in charge of his own environment."

Computer mind benders, priced anywhere from as little as $8 or $9 to more than $50, fall into four types of games: sports, educational, strategy and target. You can punt, strike out, hit a slap-shot, shoot a free-throw, pass a soccer ball, tee off and race for the Grand Prix. All with little blips that move around the screen at the press of a button.

Or, you can challenge the computer to hide numbers or letters from you. Like the old "Hangman" game you have to guess correctly, and put them in the correct order, to score. One such machine is S&R Games' "Scrabble Sensor." Coleco's "Digits 2050" and Milton Bradley's "Comp IV" play with numbers.

Several are designed as educational toys, aimed at teaching children math, spelling and more general information. "Speak and Spell," by Texas Instruments, even has a synthesized voice and a 236-word vocabulary. The voice asks you spell out a word. As you punch the letters on the keyboard, it repeats them. It says "Try again" when you make a mistake. Coleco's "Quiz Wiz" has changeable cartridges, each with 1,001 questions, covering everything from television and trivia to history, sports and movies.

Other computer games derive from popular arcade sports. You can take target practice at enemy space saucers, battleships, and so on.

Some, especially the more complex, are clearly for children only. But apparently the electronic game boom is based at least partially on its popularity with older kids as well.

"I think what the electronic toys have done is widened our demographics," said Jack Fox, director of marketing public relations with Mattel. "Adults are buying them for the kids, but end up playing with them themselves. I can work them, but when I play against my son, he consistently beats me. It's frustrating."

Give that man a set of blocks.

Most manufacturers expect this Christmas buying season to repeat last year's scene of frustration, when thousands of parents were unable to find computer games in stock. The makers of computer chips simply cannot keep up. But if your're tired of standing in line, there are plenty of other toys -- even simpler ones -- on the shelves.

Some of the most imaginative and well-made are sold at area museums. The Smithsonian Institution catalogue seems to offer not quite the variety it displayed last year. Still, $36 will buy a working steam engine kit, $7 a kit for constructing a scale-model wooden Conestoga wagon or stage coach, $20 a wooden helicopter. A 22-inch-tall panda bear costs $60, a wooden brontosaurus model $30, and from Michelle Lipson, a Washington designer, a soft pteranodon ( $8) as well as a kit for making Punch and Judy hand puppets ( $20).

The Folger Shakespeare Library, too, knows where a kid's heart lies. Stuffed unicorns, dragons and crowned lions are $45 in the large size, $25 in the small.

Even the National Trust for Historic Preservation has a selection for small people, such as an "architecturally authentic" cardboard colonial dollhouse ( $13), dollhouse plans for an Ante Bellum plantation ( $7), colonial pegwood dolls ( $21) and Shaker miniature furniture ( $8).

And the Renwick Gallery is in full Christmas form this year. The museum shop is decke in crafted toys from across the country. Mark Davis' wooden barge pull is priced at $13.50, his comical moose puzzle $14, an elephanat puzzle $10, a big fire engine with moving ladders $46.

Timothy Evans' "Ultimate Rag Doll" in a pink checked dress and cream lace is $65, "Lillian Ruffle" $145 and the "Executive Teddy," a tweed bear with a striped tie, $45. Michelle Lipson is represented with several stuffed beasts, including a big pelican for $210.

Some wilder playthings are from Padala Ltd. of Madison, Wis., and include a pizza puzzle (deep dish) of wood for $75, pick-up sticks that make a taco for $12 and other brightly colored wood peices that make an onion bagel sandwich.

Gus Kuhn's crafted wood toys include a seven-car train for $84, an antique-looking ice wagon for $35 and a "Peter Built" truck for $60. Or you can choose from Theodore Berkely's huge Victorian doll house ( $835) or Charleen Kinser's rocking ram (remember the Hobby Horse?) of genuine lambskin and pine superstructure for $950. Her giant polar bear is $400.

The best buy is definitely from the Mountain Craft Shop in New Martinsville, W. Va. a traditional wooden wagon for only $39. (Mountain Craft Shop also displays a number of wooden toys, such as a spindle top for $4.25, a climbing bear for $4.50, a flap jack for $3.50 and ball and cup for $3.75.)

And, well, what Christmas would be complete without Barbie? She's turning 21 and already, though unwed and far from her prime, has become a collector's item.

"We turn out 6 million a year," said Fox. "And 20 million garments a year. That makes us the largest maker of women's apparel in the year."

This year Mattel has introduced a Kissing Barbie, with lipstick. Press a panel on her back and she gives you a smack. It a whole lot better than changing diapers.

Pucker up, Santa.