Supermarkets, their suppliers and cooking-appliance makers have turned to an age-old marketing strategy in their competition with the fast-food industry: If you can't beat 'em, join 'em.

Joining 'em means promoting fast-food meals that consumers can cook in their own kitchens and eat in their own dining rooms. Or, as the singers warble in a commercial for Hellman's Big H Burger Sauce: "Have it at home, America. Have that restaurant-hamburger taste at home . . ."

"The fast food industry has educated the public not to cook at home," says Jeno F. Paulucci, chairman and founder of Jeno's Inc., a frozen-pizza maker. "Now the pendulum is going to swing the other way."

One company that has caught the scent of this trend is Atlas Food Systems & Services Inc. of Greenville, S.C. Atlas' What-a-Bite subsidiary, already of the maker of a frozen cheeseburger and frozen hot dog, now has come up with a frozen Breakfast on a bun.

Any resemblance between (scrambled egg, Canadian bacon and American cheese on a bun) and McDonald's Egg McMuffin (fried egg, Canadian bacon and American cheese on a English muffin) is coincidental, says Atlas president, Alex Kiriakides. "We had no intention of copying them," he says. "I don't give a damn about them."

Still, Kiriakides concedes, What-a-Bite owes part of its success ("Two shifts and still unable to meet the demand," he boasts) to fast-food res- taurants. "The only reason I'm accepted," he says, "is because supermarkets have to have something to compete" with fast-food chains.

Recapturing market share may not be easy for the supermarkets. Americans spend nearly one-third of their food dollar on meals eaten away from home, and surveys show that fast-food restaurants are increasing in popularity. Industry statistics show that between 25 percent and 30 percent of all meals consumed outside the home are eaten in fast-food places. One study indicates that 40 percent of Americans under 30 believe that food eaten away from home is at least as good as food bought in a supermarket.

The armed forces have found outway that fast food pleases young palages. Chow-line operators on the aircraft carrier saratoga were dismayed by the number of sailors skipping meals. The solution? Serve hamburgers, fried chicken, French fries, pizzas and milkshakes on quick-service lines. The result? Attendance at lunch and dinner jumped 27 percent.

"You can't take somebody and convert them to three syndrome and convert them to three squares," says Abner Salant, a civilian who is a mass-feeding specialist for the Army.

Many fast-food imitators unabashedly admit the source of their inspirations. Television commercials for the Wear-Ever Chicken Bucket, a chicken cooker made by the Wear-Ever Aluminum unit of Aluminum Co. of America, promise that chicken from the appliance "tastes like take-out." The instruction manual reinforces the message. With the Chicken Bucket, it says, "You can make fried chicken as scrumptions as any you've brought home from a carry-out."

In fact, you can make a whole fast-food meal at home. A flat, quarterpound, McDonald's-like hamburger can be made in a Presto Burger maker from National Presto Industries Inc. Or it may be a frozen Big Burger sold through supermarkets by the Glenmark unit of OSI Industries Inc., which also happens to be a major meat supplier for McDonald's. In either case, you can add Big H Burger Sauce, which tastes like McDonald's "secret sauce." And you can toss in a side order of frozen "shoestring" French fries, which more and more consumers prefer to the thicker ones.

Are the fast-food restaurants worried that their emulators will win away their customers? "Not that I know of," says a McDonald's spokesman, and even the imitators doubt that their products will do much to alter the balance between restaurant and at-home eating. "Lifestyle patterns aren't going to change because of an in-home food product," says an ad man for the Big H Burger Sauce maker, Best Foods Division of CPC International Inc. "It's not going to stop them from eating out."

The spread of fast-food eating into the home might be expected to dismay gourmets, but at least one kitchen wizard isn't unhappy. "I don't care what people cook as long as they cook at home." Says Julia Child, the well-known "French chef." A hamburger and French fries at home, she says, "might lead people to better, more interesting food; we have to look on the happy side of things."