EVERY NOW and then it's refreshing to find a spark of competition flaring in some corner of the U.S. economy. (By competition we mean the old-fashioned beat-you-at-your-own-game rather than the merge-you-out-of-business kind). Consider, for example, the war for the customer's mind and mouth now being waged by the purveyors of fast-food burgers.

The battle was touched off by Burger King, which claims in its new advertising campaign that its hamburgers not only taste better than McDonald's and Wendy's (as shown by presumably impartial tests), but are 20 percent bigger than McDonald's. Ever gracious, Burger King then offers condolences to its major competitors.

If McDonald's were on its competitive toes, it might simply reply that, whatever the tastebuds of the consumers in Burger King's survey tell them, McDonald's still out-sells Burger King three to one. Or it could try a less-is-more pitch: "Worried about your cholesterol? McDonald's is too. That's why we're putting less meat between every bun. We do it small for you." 2 But McDonald's and its co-competitor Wendy's have decided to settle the matter the American way --they're going to court. In separate lawsuits, the two firms are asking federal courts to order Burger King to cease and desist with its advertising campaign and open its consumer taste-test data to inspection. Wendy's has also challenged the other firms to participate in a tasting contest to be sponsored by an independent testing firm.

The Federal Trade Commission, the latter-day protector of truth-in-advertising, has shown admirable restraint in the matter. Noting that hamburgers are a low-cost item that consumers can easily test and compare for themselves, it suggests that the matter be left to the market. That strikes us as the best idea. Why leave the decision to a couple of federal judges or even an independently selected panel of tasters? Get out there and decide for yourselves! See you around the marketplace. Don't get ketchup on your sleeve.