Wilmer E. (Will) May was dismayed.

He had come all the way from his fast-food store in east Texas to headquarters in suburban Chicago to make one more pitch for a sure-fire menu item he and his neighboring owners wanted to sell: a simple hamburger with lettuce and tomato on top.

But the corporate guys refused, citing the reasons they had used every other time they had said no.

The idea had no class, they said. No quality, no freshness. No image. Besides, the hot burger would sizzle the veggies into mush. But May said he knew that his east Texas customers and a lot of other people on Earth wanted that lid of tomato and umbrella of lettuce, no matter what. He doggedly tucked the problem away in his mind and went about his business.

Then, one day weeks later, as he recalled it, "Out of the blue, it hit me!" A dazzling idea seized his imagination.

Excitedly, he summoned his closest colleagues. "I think I have a solution," he announced. Using ashtrays as hasty props, he placed two side by side.

"This is the base of the container," he said, hoping they could see what he saw: the ashtrays represented twin pockets of foam plastic, like a miniature TV-dinner tray.

A sizzling hamburger patty and the bottom, or "heel," of the bun would nestle in one pocket. The bun's rounded top, majestically called "the crown" in fast-food circles, would lie in insulated isolation in the other pocket, "with the lettuce, the tomato, the condiments on it."

Now, Will covered the pair of ashtrays with two more, upside down.

"These other two pieces of the package lock down . . . . They keep the cool side cool and the hot side hot!" he said.

It was spring, 1984. The McD.L.T. had just been born.

May recalled that after his brainstorming session, he took the idea to a local specialty packaging firm in east Texas. With them, he developed the idea of a sleeve-like covering over a standard McDonald's Big Mac container.

The new package was tried in his stores in Lufkin and Nacogdoches, and customers liked it. So he felt encouraged enough to show the whole thing to "corporate" at headquarters in Oak Brook, Ill.

"They got real excited," he recalled. Then McDonald's corporate idea people went to work and soon they evolved the McD.L.T. with its hinged styrofoam package that clamps together to keep heat and cold separate. The new concoction was test marketed in a number of major U.S. cities for a year and then made a nationwide menu item on Nov. 4.

The somewhat dyspeptic chronicles of American cuisine may record more profound innovations, but May's surprising notion that a sizzling hamburger and a crisp slice of tomato topped by a leaf of lettuce can be served best only if served separately has taken McDonald's -- and therefore, a good part of the nation -- by storm.

Introduced across the country with huge advertising fanfare, the McD.L.T. has become an instant favorite. McDonald's headquarters declined to say how much the new hamburger and its ad campaign would cost. But a spokesman said the price tag for the ads is "substantial."

The bifurcated hamburger-with-tomato-and-lettuce sandwich may represent the ultimate bit of insight by fast-food purveyors into what makes a nation of do-it-yourselfers tick.

In any of the nation's 6,700 McDonald's restaurants these days, hungry customers can be seen putting their hamburgers together by themselves, gingerly fishing the separated buns out of what the corporation calls May's "innovative twin-bay foam container."

McDonald's franchisees report that May's creation is accounting for more than 10 percent of their revenue. Although a corporate official said the suggested retail price is $1.49, many restaurants are selling it for as much as 20 cents higher, making the McD.L.T. one of the priciest items on McDonald's menu.

McD.L.T. arrived 30 years after the late Ray A. Kroc founded what is now a worldwide empire with annual sales of $10 billion. It has enabled McDonald's to close a gaping hole in its menu as the struggle continues with major competitors such as Burger King and Wendy's, which have reacted with acerbity.

"The McD.L.T. is an attempt to offer what Wendy's has been offering for 16 years," said Denny Lynch, a Wendy's International spokesman in Columbus, Ohio. "But they're not going to succeed, because they're just making a big deal out of a plastic box."

Denny Erwin, a Columbus Burger King franchisee and inventor of the chain's new Burger King Express restaurant-mobile, said, "They came up with the McD.L.T. to address the Whopper, the most powerful sandwich in the industry.

"Asking customers to assemble their own sandwiches is like when you buy a bicycle for your kids at Christmas and spend 10 hours putting it together."

McDonald's has a different view of what May's invention has done for the hamburger.

"Doesn't stew the tomato, doesn't wilt the lettuce or otherwise inconvenience the vegetables," said Bob Keyser, director of media relations at McDonald's world headquarters in suburban Oak Brook.

May, 45, recalled how the corporation for years sought to perfect a plain old hamburger with lettuce and tomato on top. Numerous combinations failed, seemingly permanently stymied by the heat of the cooked meat.

"By the time it was prepared and served, the hot burger kinda cooks the tomato to a certain point. It doesn't leave it crisp. They tried different things, but they never had been able to get it to meet McDonald's standards. It was just not a quality product, and we could never take it nationwide," May said.

The new sandwich each day requires 800,000 fresh tomatoes and 100,000 heads of fresh lettuce, or about 300 million tomatoes and 36 million heads of lettuce a year.

Perhaps with this giant effort in mind, McDonald's has hired William (The Refrigerator) Perry, the Chicago Bears rookie lineman and running back, to help carry the advertising ball.

Perry, who usually weighs slightly more than 300 pounds but in his collegiate days sometimes weighed much more after attacking various McDonald's entrees, will debut in a 30-second television spot during the third quarter of tonight's game between the Bears and the Miami Dolphins.

As the advertisement opens, Perry orders four McD.L.T.s, two large boxes of french fries and a Diet Coke. "A Diet Coke?" the salesgirl asks.