In the trash heaps of Tucson, William Rathje, anthropologist and admirer of Bo Diddley, continues the search for truth about the relationship between mankind and his creations.

So far he has found a diamond ring, picked up quite a following among the student body at the University of Arizona, attracted a Madison Avenue public relations firm, and found fame as the foremost clinical garbologist of our time.

For Rathje, 36, common household garbage contains the key to knowledge about ourselves. The key lies under layers of wet spaghetti, cigarette butts and decomposing melon rinds, and he and his students have been sifting through it since 1971.

Rathje calls his endeavor Le Projet du Garbage -- or The Garbage Project, a name of such grandiose preemption that it one-ups any potential put-down. To archeologists, however, trash has always been truth, and Rathje finds the formula still holds.

"For example," he said, "a survey of beer consumption conducted by interview had 85 percent of the people reporting that no beer was consumed in their household during an average week.

"Then we looked at the garbage. The garbage revealed that 25 percent of the households in this blue-collar neighborhood contained no evidence of beer. However, another 25 percent had a beer consumption rate of between one and seven cans a week. And in half the homes, we found evidence of between seven cans and a case of beer each week."

This sort of research is done by Rathje and his team at a garbage pavilion in Tucson. College students, immunized against tetanus and wearing rubber gloves and surgical masks, rip open bags of raw trash and sort through them, item by item.

"We record packaging and food debris," Rathje explained, picking up a cigarette pack from a table in a Washington hotel. "This would be a 125, for example -- made up of paper, plastic and aluminum. There are 190 code numbers, and I know all of them. Fresh fruits are a 40. Beef is a 1. I think a 4 is fish and crustaceans. Well, maybe I don't know all the numbers."

Rathje has what in college professors is often described as boyish charm, and his course is a popular one.

"Oh, the sorting can be a traumatic experience, I'm sure," he attested with the air of Tom Sawyer surveying the fence. "I think the kids who sign up are pretty aware that there's going to be kitty litter and Pampers. The ones who sign up are steeled. Even so, we lose a few from time to time."

Rathje does not deny he is probably the leading garbologist of our time. "For a long time, I was the only one," he adds.

His work is different from that of A.J. Weberman, the writer who analyzed the trash of Bob Dylan and Muhammad Ali for Esquire magazine; or that of Jay Gourley, the National Enquirer reporter who picked through Henry Kissinger's garbage.

Rathje calls Weberman's technique "Peeping Tom archeology," and deems it repugnant and redolent of invasion of privacy.

"I was asked by the TV show 'Real People' to look at Richard Nixon's garbage," he said. "I refused. I could have done it, but it would have been wrong. So they got Weberman to do it."

The ownership of garbage can be a sticky matter. In many municipalities, trash put out to the street becomes the property of the city. "We get all our garbage from city sanitation," Rathje explained. "We want to be assured of a continuing supply. But we're not getting all the trash in Tucson by any means. There are 11 million possible pickups a year, and we're only getting about 1,500."

Yes, he concedes, you can find some interesting things in garbage if you go through enough of it. And there was that diamond ring.

"It was a little one, worth maybe $125 tops. But there it was. And do you know that we had about 30 calls claiming it? You find a lot. We were hoping to start a museum of garbology. We had a whole dumpster full of interesting stuff. Unfortunately, the dumpster was emptied by mistake."

What does the presence of a diamond ring in a contemporary trash heap say to a Harvard-trained archeologist?

"It says that people take off their ring when they do the dishes and it gets rolled up with the potato peels and thrown away."

Practically speaking, The Garbage Project is a darling of industry. It is funded by, among others, Chevron and the American Paper Institute, in addition to the University of Arizona, the National Science Foundation, the Environmental Protection Agency and the United States Department of Agriculture. The paper industry is short on corrugated cardboard for recycling, and the aluminum industry wants more cans recycled, too. The Madison Avenue PR firm is paid for by the Paper Institute, which Rathje serves as consultant.

"If you look inside a cereal box and it's gray, that means the paper is recycled," Rathje is willing to explain.

Again, the value of garbology: "Recycling is very important to society, but data from interview surveys isn't accurate. For example, it was believed that higher-income people recycled more waste paper than lower-income people. Garbage proved that just wasn't true. So now the ad campaign is being geared to upper-income people too."

Garbology is being practiced from Sydney, Australia, to Havana, Rathje says, and sometimes with unforeseen results. He recently completed a study of an affluent neighborhood in Mexico City, revealing the purchase of many expensive American consumer products. "After that, President Jose' Lopez Portillo raised the luxury tax," Rathje said.

"What fascinates me is the dysfunction between what people say they do and what they do do. They're not lying -- they just don't know. The garbologist is the expert on the relationship between the material society and the idealized society."

Rathje has been asked several times in his travels just where Bo Diddley, the 1950s rhythm & blues innovator, stands on the garbology ziggurat.

"When I told People magazine that I wanted to establish a Bo Diddley Chair of Garbology, they thought I was kidding," the professor said. "But I'm not. I am a great fan of Bo Diddley. I once worked on a documentary film about his life. Bo Diddley's only consistent statement is, 'Hey man, what's in it for me?' "

Rathje cites a Diddley refrain recited in homage by the Animals on "Animal Tracks," a long-playing phonograph record. The statement is: "That's the biggest load of rubbish I ever heard in my life."

Clearly, Rathje is not bound to a moribund tradition. He got his PhD in anthropology with a dissertation on the collapse of Mayan civilization, which happened all at once between 800 and 850 A.D. Nobody -- including Rathje -- knows just why. He seems determined to keep track of where this one is going before it's too late.

"Right now, garbage has no character, no image," he lamented. "Yet garbage can make people think about themselves in a new way. It is really a terrific resource, full of paper and aluminum and information."

Perhaps Rathje will be the one to change all that. He has, after all, seen the film, "Raiders of the Lost Ark," with its swashbuckling archeologist hero.

"If there's anybody I really identify with, it's Harrison Ford," he said.