It's bigger than a Whopper. Messier than a Big Mac. Hotter and juicier than Wendy's. It's the great hamburger advertising war, matching No. 2 Burger King against No. 1 McDonald's and No. 3 Wendy's on the air and in the courts, in a battle for 11 billion consumer dollars.

A new Burger King advertising campaign, which went on the air early this week, claims that taste-test results show consumers prefer Burger King's hamburgers, which are broiled, to those of McDonald's or Wendy's, which are fried.

"At this time," a Burger King waitress says with a grin, "we'd like to offer our sympathy to McDonald's and Wendy's."

But it's not sympathy the other chains want, it's court orders to get the offending ads off the air.

Both rival restaurant chains have sued -- McDonald's filed in federal court in Miami, Wendy's in Columbus -- charging that the ads are unfair and misleading. McDonald's says Burger King burgers are often steamed, or reheated in microwave ovens; Wendy's says its own tests show consumers have preferred Wendy's burgers, which are cooked to order, in each of the past 10 quarters.

There's a lot more than pickle chips riding on the outcome. McDonald's reported worldwide sales of over $7 billion in its 6,905 restaurants last year. Burger King, a division of Pillsbury Inc., had $2.3 billion in sales in 3,255 stores. Wendy's, third in hamburgers but fifth in overall fast-food sales behind Kentucky Fried Chicken and the Marriott Corp. combination of Roy Rogers and Big Boy, reported sales of $1.4 billion in 2,350 stores.

Burger King touched off the sizzling dispute with its aggressive new ad campaign, created by J. Walter Thompson Inc., the same agency that developed the live taste comparison campaign for Schlitz beer. Advertising industry sources said Burger King, which spent about $36 million on television commercials last year, is planning an increase of 12 to 15 percent in its advertising budget this year.

In one of the ads, a little girl complains that McDonald's hamburgers are 20 percent smaller than Burger King's. In another, prepared for airing during the World Series, a Burger King waitress tosses a baseball into a mitt as she talks about research data purportedly showing customer preference for broiled burgers.

The one that especially seems to have stung the competition opens with a Burger King employe offering condolences to McDonald's and Wendy's because "the Whopper beat the Big Mac for best taste overall among consumers of both burgers. In a similar test we beat Wendy's single. Now that may have surprised McDonald's and Wendy's, so we just wanted to say, it's okay, guys. Winning isn't everything, but it sure is fun."

McDonald's and Wendy's both challenged the validity of the research that Burger King says is the basis for its taste-preference claims. In the Miami case, McDonald's has demanded access to the data, and a spokesman for Burger King says it will be made available after a court hearing to determine how much material McDonald's is entitled to.

Wendy's went beyond suing to challenge both rivals to join in sponsoring a survey by an independent testing firm to see which burgers consumers really do prefer. "There's no risk to us in doing it," Wendy's Chairman Robert L. Barney said yesterday. "We know people are going to say we have the best hamburger."

Barney, in a telephone interview from his office in Dublin, Ohio, said Wendy's "maintains a national tracking study. We ask a cross-section of people, every month, which they prefer, and I can show you for the last 10 quarters, Wendy's has come out with the best-tasting hamburger every time."

Wendy's single-pattie burger, he said, "has 10 percent more meat" than Burger King's double-deck Whopper. "Their patties are 3.6 ounces, ours is 4 ounces," he said. "Ours is fresh meat, theirs is usually frozen."

Neither McDonald's nor Wendy's has complained to the Federal Trade Commission, which in the past has exercised jurisdiction in truth-in-advertising cases.

"We usually don't get involved in cases of comparative claims," an FTC spokesman said, "because it's a subjective judgment. Anyway, the hamburger is a low-cost item. For a buck, the consumer can afford to find out if Burger King tastes better than McDonald's."