WHEN WE first got married Eliot's mother told me he should be a lighthouse keeper, that he didn't much like people. But that didn't stop me." This is Aline Porter talking - painter, mother of three grown sons and for the last 41 years bemused wife to the world's most acclaimed nature photographer. And the photographer himself? What does he say?

"Well," begins Elliot Porter softly, his voice like finely cracked leather, " for some reason I've always been more affected by the simple beauty of birds than by all the unexplained questions of human life. I'm sure some people would say it's not very important on the onthe scale of things, shooting pictures of birds and flowers and trees. But what is important? Making shoes? I guess birds epitomize for me everything about the universe that's free and wild. And that's why I love them. . . "

SANTA FE, N.M. - He lives off a dirt road, in a grove of old cottonwoods and catalpas and Chinese elms.The place is a Spanish adobe, made of sundried brick and great wooden beams. There are broad patios and porches and windows and fling wide in summer. Somehow, all of it seems indigenous - as if man and house just grew up there, like cacti, on the desert sand.

The mountains seem indigenous, too.They are named the Sangre de Cristos (blood of Christ), and later, when the sun has drilled a pth across the hazeless, blue sky, those mountains behind Eliot Porter's home will glow soft, like red lanterns. Farther South, in Albuquerque, where the air is not so bracing nor the altitude as high, there is another range of mountains - the Sandias. Their color at sunset is a faint pink. Sandia is an Indain word for watermelon, says Porter, savoring the correctness of the name with a small, spare smile.

The 76-year-old Harvard-trained physician, who gave up medicine a lifetime ago to begin studying the deeper mysteries of the outdoors, is at work in his studio this morning. He wears a shirt bleached pale from too many launderings, a handsome, hand-tooled belt, white socks. His deeply browned skin has a fine, dry flakiness to it - a badge of all those seasons in the sun. When he smiles, his fare cracks and seams like an old ball mitt.

The studio, which adjoines the house, is an unadorned place too - with unfinished, wooden chairs and great solid tables occupying stacks of papers and books. Covering one wall are nearly floor-to-ceiling drawers of the prints that have filled up calendars and books over the years. In a separate room, giving traces perhaps to his former life, are shelved issues of Scientific American; they go back decades.

Books such as "Baja California - the Geography of Hope." "Forever Wild - the Adirondacks." "Down the Colorado." "Galapagos - the Flow of Wilderness." "Summer Island - Penobscot County." Not to speak of his crowning "Birds of North America," a work Porter once said he "struggled and worried over for nearly half a century." (In the book's introduction, he writes of "the indefinable longing that is aroused in me by close association with birds.")

And in the center of the room, on the tables, the first fruits of books still coming - on his adopted New Mexico on Grecian archeology, on Antarctica, on the America landscape that he intends to catalog from shore to shore. At an age when most men are busy tying tomatoe vines, or doddering in a rest home, Eliot Porter is making long-range plans.

Out in the yard a bird is warbling. What kind is it the visitor asks. Porter, hands in the pockets of his old twill trousers, suddenly cocks his head - a pointer on scent. He is as attentive as a surgeon now, advancing stealthily toward the door in his crepe-soled shoes. He seems oblivious to everything save the sound.

"I think it's a house finch," he says at length. "But it could be a vireo - maybe a solitary, maybe a warbling, I'm not sure. Over there, in that cottonwood. Listen." He waits for the song to come floating in again, then says: "Course, I'm not as good at identification as I once was. My direction and hearing's going some. It's an inevitability of age . . . I guess." This last he tacks on, reluctantly.

Before going into the house again, he stops on the patio to check a project. "I've been shooting male humingbirds," he says. "They're a very cavalier bird, you know. Won't go near the nest. Anyway, I rigged up this photo-electric device with my 4x8 Linhof, which is mostly what I use now, so that when the males come darting in for the sugar water that I've set up in bottles around here, they'll trip the cell and I'll get a picture automatically."

Suddenly he is grinning like Groucho.

Sure enough, a bird with brilliant, iridescent-red coloring and wings beating furiously comes humming into the yard a moment later. The creature, no larger that Elliot's index finger, hangs suspended for an instant at the bottle's neck. The click of the camera startles him, and he bolts away. But it is too late: The bird-man of Santa Fe has got his picture.

Back in the house, he is asked rather fumblingly how he came to know so much about nature. "But I don't know so much about nature," Porter says quickly. "There's always something going on out there you're just discovering. Thoreau wrote about that, how new it always seems. What did he say - "This curious world which we inhabit is more wonderful than it is convenient?"

He pauses wanting to add more. His wire-rims are off and he is squinting at the desert sky and the blood-red mountains. "What I do is simply walk around the woods and look for things.It's instinctive - like hitting a tennis ball, maybe. You don't really know how you do it - you just do it. Or catching a fly ball. Bang. It comes down in front of you and you catch it. I mean I would fumble.

"Look: So many photographers talk about 'seeing' or their 'eye'. I think it's rather self-conscious baloney, that kind of ingot. If you ask me reviews and statements by photographers are all very boring. Tiresome. I read Aperture magazine and that's it. I mean, you can see what a photographer does in his pictures. That's enough."

But how do you know where to go for a picture? Is it only instinct?

He looks amused. "What good nature photography takes is long hours of quiet sitting in the woods. Until you and the camera become accepted as part of the surroundings. And then you must be aware. For instance: you see a bird pack up a stick. Okay, that means something. If it's female, it can mean she's building a nest somewhere. You get your binoculars out and you put them on that bird and the next thing you know she's disappeared up the canyon, and you think. "My God, I'll never find that nest now." But at least you have a direction, don't you?"

It is a useless tack genius needn't explain itself. In a 1979 essay in Modern Photography magazine. Porter's fellow Western photographer and close friends, Ansel Adams, said: "He has that kind of intuition which captures the moment of importance and conviction." Put another way: Eliot Porter knows exactly what is there whent the shutter lets in a moment of experience.

At least once Porter himself tried discoursing on this; the key as he saw it, was something; called "emotion": "It is not permissable to impute love and hate, or joy and sorrow, or even anxiety and contentment to a bird. An ornithologist does not acknowledge that a bird has emotions. A bird is only a bundle of reflexes and instints to him. Nevertheless, because birds behave as though they did have emotions, because they appear at times nervous and anxious, distressed and unhappy, they have a meaning in terms of which bird behaviour is interpretable. . . ")

Of course, Eliot Porter wasn't always so lionized. There were the early years when nothing much happened when he had sold a couple of bird photos and that was all. People must have been wondering why a man would give up a promising career in biochemistry (he had been teaching at Harvard for a decade, quietly comfortable in the bookish world of Cambridge to go out West to shoot pictures of wildlife.

In color, no less. The esthetes of the day were all shooting in black and white as most of them still are, rejecting color on the grounds it imposed a deadly literalism. Porter rejected that. Buoyed by the renowned Alfred Stieglitz - who had first exhibited him in 1939 at New York's An American place gallery - the young Porter and his wife of three years pulled up stakes and went to New Mexico, a land he'd never seen. It was an odd thing for ghe son of a prosperous Midwestern architect to do. But the doctor had made up his mind. After all, his brother, Fairfield Wadsworth porter (who died in 1975, had made up his deciding to become a painter. Why couldn't Eliot shoot pictures?

The break came with the publication by the Sierra Club, 1962 of "In Wildness Is the Preservation of the World." The book linked spectacular Porter photos with just as spectacular passages from Thoreau. The resutl was an almost immediate international reputation for both the Sierra Club, therefore a little-known conservationist group, and the author.

Since then, of course, there have been dozens of other Porter projects, each with an insistently louder plea for the preservation of the earth's wilderness, each bearing Thoreau's implicit theme that the only proper context for human life is nature itself. In a way, it was as if the two naturalists, the one writing in the middle of the 19th century, the other photographing in the middle of the 20th, had become inseparably entwined.

A few years ago, in The New York Times. Porter let his rage burn to fine white heat. He was talking about the destruction of Glen Canyon on the Colorado, a place he had photographed years earlier. "What we received in exchange fro the loss of Glen Canyon," he said, "is a featureless sheet of water, a dead basin into which all the flotsam from the surrounding land accumulates with no place to go. It is a haven for those rich enough to have motorboats. Otherwise, it's a dead lake that has replaced living water."

He is asked about that now, and whether time has doused his anger any. His answer is the most indirect and eloquent of replies:

"You know, when I started all this nearly a half century ago. I think I informally joined what might be called the 'straight' school of photography. Ansel Adams, Edward Weston - those fellows. I'm interested in recording nature, you see. You take the old-fashioned naturalist. He really was interested in the full range of Science. Well, I know that getting pictures 'right' was nudes. I don't shoot babies. I don't shoot street ladies. I shoot nature. Why? Because I know it's infinite, that it will be here long after all of us and all of my work has gone to dust. I'm just trying to get down alittle of it while I'm still around. . "