He has a briefcase and a pipe and a tweedy coat. That seems all wrong. Richard Leakey senses the disappointment. People are forever trying to make a romance of this work, he shrugs. They want khaki shorts and a Land Rover. "I should like to disabuse that."

Actually, Richard Leakey, whose work is puzzling out the secrets of man's origins, does pretty well in spite of himself in making it all sound romantic. Ask, for instance, for a picture of his fossil-hunting camp at Koobi Fora, on the banks of Lake Turkana in northern Kenya, and he will paint a fierce Impressionist canvas of yellow-green spiking grass and languid crocodiles and mountains baking under a brittle blue sky. At night the wind comes up, and it is cool.

"The camp is on a spit and so the lake is before and behind the camp," he says with a pleasant-sounding colonial British accent. "The camp faces north so that one in fact gets the passage of the sun continually changing colors on the water. You can stand out there and in half an hour the lake will go from blue to green to brown to what is nearly a pewter gray."

Leakey is 33. He is heir to the most famous genes in modern antropology. Quick and polite, he conducts himself in that sure, almost sporty British way, tucking a parenthesis here, inserting a phrase like "the quote, women's lib, unquote, movement" there, begging off any claim to authority, yet by virtue of his name and intellect and polish being one just the same.

He likes to hold doors and thank you quite a lot. He is tall and rangy. Brown hair licks down the back of his neck. He is a third generation Kenyan and is proud of it.

He's come to the States this time (he averages a couple hops a year) to hold meetings on the museum he heads and to chat about his new book, "People of the Lake," written in conjunction with Roger Lewin, science editor of the New Scientist magazine in London.

He likes America, he says. It's vital and it's one of the few countries where you can get something done. Arbitrary place, though: The cafe he's just stepped into, and out of, closes down from 11 to 11:45 everyday. "See what I mean?"

After stops in Chicago and L.A., he will fly to London, then home to Nairobi. A few days after that Leakey will pilot his single-engine Cessna up to the fossil site. He's anxious to get back.

Can we pinpoint the specific time man became man?

"Somewhat of a semantic discussion don't you think? I don't know anyone who's really certain when mankind became mankind - or even what it is. Certainly we know what we are - Homo sapiens. "

Was the Garden of Eden in East Africa?

"I don't think there was one, do you? You do? Well, if you wish a Garden of Eden, you have to put it in Africa. But I do think it was a big garden. A big garden."

He says this smiling and leaning in a centimeter.

This isn't to suggest Leakey is not a serious, even intense, human being. In the past 10 years, on a combination of drive and what he calls dumb luck, he has moved himself to the forefront of modern cultural anthropology, making striking fossil discoveries, writing books, postulating new and unpopular theories (a chief one being that Homo sapiens doesn't necessarily have agression in his bones), threatening, some say, to eclipse even the sacrosanct reputation of the two people who raised him.

His father, Dr. Louis B. Leakey pioneer in research of Homo habilis (handy man), an important link with that other hominid, Homo erectus, died in 1972. But Mary Leakey, his tough, cigar-smoking widow, is still known to put in a full day on the sites, one of which is the Olduvai Gorge on the Serengeti Plain in Tanzania, where she and her husband were digging for fossils as much as 40 years ago. Mother and son don't mix in their professional lives; never have. There was a time when father and son barely spoke.

"If one wants to put it simply in those terms, it may have happened in some areas already, this eclipsing business," Leakey says cautiously, ural, happy way

"but the work is different, too."

On one hand, it might seem the natural, happy way of things for a son following in his father's footsteps to eventually overtake him. Even if the father was the powerful, crotchety, charismatic Louis Leakey. In this case, the son happens to be unschooled in the profession, lacking any formal higher studies whatever.

Richard Leakey left the Nairobi public schools at 17 to set up a safari business (which became highly successful). About the only thing he was sure of back then was that he wouldn't follow in his father's footsteps. "One felt a little intimidated," he says. From the time he was six months old, he and his brothers, Philip and Jonathan, were being carted around on expeditions.

"I just wanted to get out - go away and look at animals. But it passed. The time came."

He sounds matured now in his attitude toward his parents. "In my own mind, nothing I do will ever cast a shadow on my father's accomplishments," he says at one point. At another, he says his mother, primarily an archeologist, is about the best in her field - though it's a new field now, with things like clinical lab analyses, and she's of the old school.

He pauses suddenly; his voice as kind. "You know, my parents worked at Olduvai Gorge from 1931 to 1959 without making an important discovery. I found fossils a couple years out. A lot of it is just luck."

Leakey seems inversely proud not to have academic initials tacked after his name. He likes saying he's learned it all on the job, that he's "not an 'ist' of anything." He suspects a few anthropologists still consider him a spoiled upstart; his rapport with most academics is fine. "I don't think I'm being patronized or tolerated." In fact, they might all be envious. Last year he made the cover of Time - and got 9,000 letters.

What is surprising about Richard Leakey is that he's only a part-time anthropologist. His real job is directing the National Museum of Kenya, a post he's held since 1968. This means he lives most of the time in Nairobi and goes to work as a bureaucrat. Three hundred people work for him, he says. "Lots of brunches and that sort of thing.

"My feeling is you can't have a research project like ours at Turkana without a solid financial base. Well, we've established that."

You'd rather do the other?

Through pipe smoke and with great measure: "Actually, I don't think I've done anything I haven't wanted to do for a long time."

Leakey is married to an anthropologist. Meave Leakey did her PhD in Wales. The two have two children. There is another child by an earlier marriage, which ended in divorce.

He is not a man of religion, though his grandparents on his father's side came to Kenya as missionaries and though a few uncles are Episcopal clergymen. Contemplating ancestors who lived 3 to 5 million years ago and who survive today as crinkly fragments of bone hasn't made him believe in an afterlife, he says.

"What happens after death? I don't think anything needs happen."

Agnosticism or atheism aside, there is a moral current running in Leakey. Altruism, he calls it. One of the conclusions of "People of the Lake" is that war "is not a biological inevitability" and that the more one studies prehistory the more he can be convinced that early man led a life based on sharing and order and thoughtful adaptation. "In its gradual emergence from the animal kingdom, humanity invented a new game, and that game is called culture," he writes.

But no one really knows: "Behavior doesn't fossilize." He likes that. A bon mot.

The view of altruistic man runs counter to the more vogue view espoused by men like Robert Ardrey ("The Territorial Imperative") and Konrad Lorenz ("On Agression") who feel the tie that binds is hostility. Greed and murder are just in the genes.

"I've become appalled at the ease in which masses of people can be led to beliefs," Leakey says. "The way this agression idea has been portrayed the last 10 years is astounding. I mean, you talk with cab drivers or policemen or Sunday school teachers and they'll tell you this is just the way it is. I must take exception."

He also must take exception to the belief that Homo sapiens, like so many other living organisms in history, will inevitably become extinct. We may be here by chance, but we alone have the means to save ourselves: We can reflect. On our past and on our future.

"That ability might separate us from the pattern."