Brandishing their disapproval the way King Arthur brandished the sword Excalibur, some would-be reformers are making much of the fact that House and Senate candidates spent $300 million in 1982 campaigns, mostly to fill the air with words, many of which were derogatory. But before the number $300 million makes you faint, consider, for perspective, the autumn's costliest ($19 million) negative advertising campaign.

Burger King believes this would be a better, sweeter world if more people ate Burger King hamburgers. But the civilization-shaking fact is that many Americans are tired of hamburgers. The average American eats 19 pounds of hamburger a year, but that is up a measly 10 percent since 1971. Hamburgers account for only 40-45 percent of Wendy's sales, down from 60 percent just four years ago. Burger King has even begun selling veal parmigiana sandwiches.

With half of American women working outside the home, lots of Americans are eating out, and bringing cooked food home. But many persons who used to be teen-agers and who used to be content with ordinary fast food have quit being teen-agers -- some have even begat teen-agers -- and now want waiters, tablecloths, alcohol and something other than hamburgers. Furthermore, as you may have noticed, America's roadsides are saturated: the best sites for fast-food franchises are filled with fast-food franchises, so expansion is not easy.

I have told you all this in pitiless detail to make intelligible Burger King's recent advertising. Faced with a stagnant market, Burger King launched a negative campaign against McDonald's and Wendy's, claiming, among other things, that "independent taste tests" proved that Americans prefer Burger King's "Whopper" to McDonald's and Wendy's comparable products.

Negative advertising often succeeds, in part because people tend to confuse rudeness with sincerity and to equate sincerity with high principle. But Ronald McDonald is no human doormat. Flames poured from his nostrils and, good American that he is, he did the American thing: he sued. He said, as Hamlet used to go around saying (not about Burger King, of course) that Burger King's offense was rank and smelled to heaven. When the smoke had cleared, the courts had departed from established policy and had behaved sensibly. That is, they had done almost nothing.

McDonald's, which outsells Burger King three to one, argued that Burger King's claims were unsubstantiated. McDonald's can retaliate with some negative advertising. Last year McDonald's spent $322 million on advertising.

Note that number. McDonald's -- one corporation in one industry -- spent more on advertising in one year than was spent contesting 468 seats in the national legislature. In fact, the nation's largest advertiser, Procter & Gamble, spent about $670 million in 1981. The soft- drink industry spent more than $300 million. A corporation that spent just $300 million would rank only ninth among corporate advertisers.

Americans spend five times $300 million -- $1.5 billion -- on chewing gum in a year. What is so shocking about spending $300 million on political speech about who should make the federal laws? Audible political speech depends on political spending. Today, pornographers enjoy a virtually illimitable right of "expression," but the quantity of effective political speech is regulated by laws limiting campaign spending. Granted, much political speech is not elevating. But that is an argument for better, not less, political speech.

How effective is advertising? That depends on the product advertised. In politics in 1982, many of the big spenders lost. McDonald's advertises a lot and sells a lot. Advertising helps get people into the restaurants, at least the first time. But McDonald's sells more than a billion hamburgers every three months; the average McDonald's grosses more than $1 million a year. Fast-food chains depend on repeat business. Among advanced thinkers, it is considered brave to defend and perverse to extol fast food. But people keep coming back for more. Advertising cannot make them do that, or anything else.

Politicians tell this story: a man decided to manufacture dog food. He said: "I'll use all the selling arts. I'll design an alluring can, an eye- arresting label, catchy slogans and jingles. I'll blanket the media with advertising, I'll use coupons and direct mail, and have conspicuous displays in all the stores." He did all this, but the stuff sold sluggishly. So he went to a pet store and asked: "Why?" The store manager answered: "The dogs don't like it."

Moral: there are limits to what merchandising can do. That speaks well of American dogs and other discerning consumers, including voters.