A love affair with 'Life on Earth'

David Attenborough, the man who is giving new meaning to ''Life on Earth,'' admits that he is ''a compulsive lapel-snatcher.''

''If something interesting happens,'' he says a bit shamefacedly, ''I want to dash out into the street, find somebody, grab him by the lapel, and yell, 'I say , I've just made the most fantastic discovery . . . .' ''

In his 13-part zoological series, ''Life on Earth'' (PBS, Tuesdays, 8-9 p.m. - premiere tonight - check local listings for initial airing and repeats), Mr. Attenborough does for more than 5 million PBS viewers in the United States what he did for captivated BBC viewers in Britain a couple of years ago.

There is much that is sandy about Attenborough - sandy hair, sand-colored shirt and trousers, shod in, appropriately enough, desert boots. But there is nothing sandy or gritty about his mind - as clear as the fresh well-water. If you are a PBS buff, you will probably remember him as the host and narrator of ''The Tribal'' in 1975.

If somebody has to choose between reading his book version of the show (Little, Brown), or seeing the television show, which would he advise?

Attenborough squirms on his sofa in his Waldorf Towers suite like a boy forced to pay attention in class, running his fingers through that sandy hair, using his hands and his whole body to express with a slight British stammer what is on his inquisitive mind.

''They are very different things and serve different purposes,'' he said. ''After all, the word and the image are not interchangeable. One thing I hope is that publishers do not reach a point where they will not publish a book unless it is a megabook - that is, tied in with a television show.

''A lot of people in England watched the series with the book on their laps and I don't think it did any harm to the show, the book, or the people.''

According to Attenborough, in doing the series he had to rethink the dialectic of life on earth. ''I sat down and in about nine months wrote the outline script for all 13 shows. And then, in order to film them, I started traveling.''

Kenneth Clarke of ''Civilisation'' and Jacob Bronowski of ''The Ascent of Man'' were academics. Although Attenborough has a degree in zoology from Cambridge, how is he qualified to write a book and host a series about the origins of life?

''Naturally, I must be competent in zoology. But also good with animals on camera. And for 10 years before I came to BBC in 1952, I made natural history films. That prepared me as nothing else would.''

What does Attenborough hope the series will mean to the American viewers?

He combs his hair with his fingers and repositions a copy of the airmail edition of the London Telegraph on the table before him. ''The misunderstanding of the natural world is very great among humans, British or American. It is not enough that strange animal habits are extremely fascinating to people, but it is very important that people should also understand the complexity of the natural world.''

Does Attenborough - who, by the way, is the brother of actor-director Richard Attenborough - consider himself a writer or a broadcaster?

''No problem there - a broadcaster.''

But did he enjoy writing the book?

''No. I don't enjoy writing. It is awful. And the first line I write always looks so banal and silly. But when you do a film - well, it is exciting from start to finish.''

In the course of doing the series did he have any experiences which permanently affected his relationship to the world's creatures?

''There were many. But the one which I remember most vividly was an experience with gorillas in which I was almost accepted into their society.

''It was a moving experience for me, because I know how difficult it is to get into the mind of another human being, much less another animal. We deceive ourselves when we think we understand what our dog sees. The dog lives in a world of aromas and is prisoner of all kinds of instincts which are totally closed to us.

''If there is any way to arrange some sort of true communion between yourself and another nonhuman animal it would be with gorillas. They see the world much as we do. They stand upright. They have two eyes. Their bodies are much the same as ours. They live in family units much the same as we do. They have dominance patterns resembling ours. They have the same kind of manners in a sense. Their facial expressions convey very much the same things as ours do.

''There was a moment when I suddenly felt I had actually transcended the human condition, that I was actually able to see what the world looked like in a nonhuman way. When I looked at the film and wrote about it, I realized that I had almost comprehended the reality of another organism.''

As a zoologist, how does Mr. Attenborough feel about zoos?

''I think zoos have at least two very important functions. They can act as refuges for endangered species. And they serve to remind urban people, cut off from the natural world, that such creatures as elephants exist, and that it is of consequence that they continue to exist.

''And now having said all that, if you are as lucky as I am and you go around the world seeing the wild animals in their natural habitat, it is unbearable to see a gorilla in a cage.''

If this, author-TV producer-zoologist were to choose one creature in the world with which he most identifies, what would it be?

He smiles, then scratches his head, combing through his hair a bit like certain wild creatures of the jungle.

''A chimpanzee, I guess,'' he says with a smile, and self-consciously stops his grooming movements. ''Sort of mindlessly curious about things and prone to fly into rages and irrational tempers.''