Where else but in Southern California can mom pile the kids into the car, buy the weeks groceries, a pair of shoe laces or two, a few kitchen utensils and then sit down in a corner of the same store for lunch: Tuna sandwich with a milkshake for one of the kids, a "quarter pounder" with a soft drink, for the other and for mom a health salad with a cup of coffee.

Supermarkets and food processors, afraid they are losing business to the McDonald's, Arby's and Seven Eleven's of the fast food business, are fighting back.

Especially in California they are experimenting with eat-in areas inside stores. No one is quite sure if the experiment will be profitable. In addition, all over the country supermarkets have greatly expanded their prepared food sections for carry outs along with in-store promotions and newspaper advertising making price comparisons in an attempt to counter a trend that finds Americans eating one out of every five meals in some sort of restaurant. A little more than a third of the food dollar is spent on meals away from home and the National Restarant Association estimates the figure will rise to $2 out of every $5 by 1980.

That money must come from somewhere else and the grocery stores figure they are the somewhere.

Los Angeles is one of the country's most competitive markets and the efforts of supermarkets to counter this trend are far more evident than in Washington. A large Los Angeles chain, Ralph's, is putting carry-out and eat in facilities in its big new stores. The 60,000-foot operations, called Villa Grandes, are twice the size of the ordinary supermarket. They sell everything from toasters and sneakers to liquor and cereals.

One such eat-in operation has six tables, each with four chairs, situated at the end of an extensive prepared food section that offers a variety of cheeses, deli meats, salads and barbecue. One of the tables even has a computer game top to amuse customers while they munch on lox and cream cheese for $2.25 or a combination sandwich of roast beef, turkey and Swiss with potato salad and a pickle at $2.19. Those who don't want to play games can contemplate the Italian grocery display. There are the usual drinks, cookies and pastries for dessert or a dish of frozen yogurt at 45 cents.

Elsewhere in the store a thirsty shopper can pick up chilled beer, wine and soda, even a shrink-pack containing a plastic glass and a six-ounce bottle of wine.

At a Boy's Market in another part of town, a small canopied sidewalk cafe, enclosed by grillwork and decorated with murals and window boxes filled with dying plants, beckons the fited shopper. Outside signs invite shoppers to: "Relax and enjoy one of our gigantic pastrami sandwiches," which are " . . . bigger and gooder than anybody's!"

The store has a 64-foot bakery counter at one entrance. Across the aisle is a three-sided deli counter where signs urge customers to buy carry-out food: "Lunch for the office bunch? Order by phone. Sandwiches to go."

At the other entrance, in the liquor department, chilled wine, beer and soda sit side-by-side with cartons of milk and orange juice.

Eat-in sections at Alpha Beta stores are modernized versions of an operation common to the large California chain 50 years ago. According to Esther Cramer, consumer specialist for Alpha-Beta, some of the stores, especially those in the rural areas, had snack counters before the Depression. They were a convenience to farmers who would come to town for once-a-week shopping.

Such operations were phased out of most Alpha-Betas, but now they are making a comeback to give shoppers in a hurry a place for a quick bite.

"The Hungry Shopper" offers weekly specials: corned beef sandwich with potato salad or cole slaw, a pickle and a "free small soft drink" for the same price as the sandwich alone, $1.59, along with several other sandwiches and the usual prepared foods. For those who don't want to sit down at one of several tables provided, there are sectioned styrofoam carryout containers.

What must be the most extensive eat-in and carry-out operation in a Los Angeles store selling groceries is found at a membership store called Fedco. It carries dry goods, hardware, just about everything, and the grocery section is relatively small. By comparison the eat-in area is a true cafeteria with tables and a snack bar. Hot dogs, pizza slices and hot soft pretzels are available on one side; a hot food line on the other. Shoppers can buy a Reuben sandwich there for $1.69; a bowl of chili with beans and crackers for 98 cents; a stuffed pepper dinner with salad, potato, roll and butter for 99 cents.

Elsewhere are pizzas to go, baked or unbaked, and a complete counter devoted to several kinds of popcorn and candied apples.

Pre-prepared Poor Boy sandwiches and $1.49 "Pounders" that contain "salami, bologna, Swiss cheese and other assorted meats, sliced pickle and Italian dressing" are available at the deli counter located at the store's only exit. Fried chicken pieces, lasagna portions, manicotti, many of the foods found in large delicatessens, are also sold. The bakery counter is on the other side of the exit.

None of the eat-in operation is likely to give a Sans Souci, or even an Emersons, a run for the money. But then they are not in competition with them. And they certainly are no better or worse than the fast food operations with which they are trying to compete. Though their service is not as speedy, they offer a greater variety of food.

While some Washington-area stores have extensive prepared food counters and bakeries, few make sandwiches to go. The only stores in which such carry-out food is featured are those located in the downtown business district and within office buildings such as the L'Enfant Plaze complex. Most, if not all, are Safeway's Town House stores, smaller and more expensive versions of the parent operation. Instore restaurants are unknown in Washington.

Esther Cramer from Alpha-Beta said she is not certain in-store restaurants are the best way to complete with the fast-food business. The rest of the supermarket industry isn't certain either. Less than 11 per cent of all the new supermarkets opened last year have such facilities.

About the expanded deli-bakery there seems to be no such questions. All those visited in Los Angeles offer some kind of catering, often specializing in 6-and 12-foot subs.

Elsewhere in the country, supermarkets are competing with fast-food restaurants on the basis of price. The cost of eating out has risen, on average, about twice as fast as the cost of food at the grocery store.

An ad campaign at Boston's Purity Supreme Supermarkets asks: "Who pays when they do it all for you?" This is a direct reference to the McDonald's commercial. The store's ad says a total dinner for four at a fast-food outlet costs $7.95 compared to $3.72 for the same meal at home. "There's no price like home. You never forget how good home cooking is. Maybe you just forgot how little it costs."

Florida's Publix Supermarkets advertise their fried chicken in a bucket, similar to the one used by a fast-food chain. The bucket contains a $1 sales slip and the ad asks: "Is the price of take-out chicken hard to swallow?"

Their answer: "Maybe it's because you're paying up to a dollar extra for the name on the bucket. At Publix nine pieces of crisp Southern fried chicken cost less that $2.75."

Some food processors are joining in the campaign. Banquet Foods is using an "Eat In and Bank It" slogan for its frozen prepared foods.

At least observer thinks the food industry may be responsible for the predicament in which it finds itself.

Joan Gussow, chairman of the nutrition education program at Columbia University's Teachers College, told a recent consumer-industry conference that the food industry's advertising probably had driven the public to fast-food restaurants and carry-outs. Said Gussow: "What has been sold by food producers on television is saving time, eating quickly and satisfying your family and if you sell that you may be hoisted by your own petard . . . You may find you have solid fast foods so effectively that the fastest foods are out and people are going to stop cooking at home at all and go out and eat.

"I give just a word of advice to food marketers," Gussow said: "Maybe they should start emphasizing the great pleasure of standing around the kitchen en famille and cooking."