PETER MATTHIESSEN is a prodigious purveyor of expertise. He imports it, he discovers it, he revels in it. Turtle fishing? Just check into Far Tortuga, a previous work of fiction. Himalayan travel? There's the award winning The Snow Leopard. And of course if you like white sharks, you'll love Blue Meridian. The point is that Matthiessen is a writer with a great deal of confidence. Who else can bring out a book from either side of the world examining two states of art in the same year?

Nine-Headed Dragon River is a book about Zen. Zen, which is short for Zen Buddhism and short, too, for "zazen" which means sitting meditation, and which is the most familiar expression of it to us Westerners, did not die with the '60s. It just dropped out of sight, where it is probably a good deal more comfortable.

Men's Lives is a book about the indigenous fishermen of the far eastern tip of Long Island, a part of the world now dominated by the superwealthy of New York. The remaining fishermen and clammers are the area's white trash, not to quibble about it; their natural prey is the white-fleshed striped bass.

Crude-spoken, sometimes offensive, sometimes anti-Semitic, always disreputable (to the increasingly upscale inhabitants who have claimed this New England-oriented part of Long Island), the fishermen, known as "Poseys" and "Bonakers" among themselves, depending on their relations and birthplace, are the salt of the earth to Matthiessen, who himself fished professionally -- and later as a sideline -- during the early '50s.

Both of these books are remarkable, memorable nonfiction. They are what nonfiction can be when the author lets his subject speak, and when he has gained enough knowledge to write with confidence about subjects which are not well known. Matthiessen's prose is as strong and pure as ever.

Take Zen. Dragon River is a Zen book, as the author warns, "A Zen book composed against the best instincts of its author, who has no business writing upon a subject so incompletely understood -- far less a subject such as Zen which is fundamentally impossible to write about." However, Matthiessen reports in the next sentence, he has practiced this intellectual's religion for 15 years; these are his journals, the diary of an amateur enthusiast and more than that, and he was introduced to Zen through the shared experience of the death of his wife Deborah Love from cancer. That death was tormented, as such things are in this country by lies, chemicals, radiation, drugs. ("I could not clear my nostrils of the stink of flowers in the cancer ward, the floor shine on that corridor of death," he writes.) Yet he and she were sustained by Zen.

He later went on a pilgrimage to Japan (which is the source of U.S. Zen, though itself a late inheritor of the religion from China and the Indian subcontinent) to meet and see the temples and the persons of great practitioners. Forty-eight pages of this journey are lifted straight from Snow Leopard, which was published in 1978 to wide acclaim.

His is the enthusiasm of the West for the East. He believes; he plunges into the lore; he longs for a great experience; he meditates, learning the painful "zazen" discipline of sitting absolutely still for hours; he tries to subdue his old weaknesses ("greed, anger and folly"), and for a time achieves a state of grace: "In the midmorning sittings, I become a sapling pine, warmed by the sun, swaying in the wind, inhaling wind, water, minerals, exhaling warm, fragrant amber resin. Tough roots budge subterranean rock, the trunk expands, sinewy limbs gather in sunlight far above, new needles shining in new sun, new wind, until the great pine is immovable, yet flexible and live, the taproot boring ever deeper into the earth. Then the tree evaporates and there is nothing, and nothing missing, only emptiness and light."

To many, Zen will always be an annoying import. They are truly foreign to the Western mind, these "nonlinear Eastern perceptions." These endless, sententious Haiku (three lines, 17 syllables) poems and veiled pronunciamentos: "All are nothing but flowers/ In a flowering universe."

Luckily, we have the profoundly Western mind of Matthiessen emptying out his notebooks in beautiful sentences, or else this book might be far more than anyone ever wanted to know about Zen. The link, and the theme which joins Nine-Headed Dragon River to Men's Lives, is the idea of personal discipline. THE THOUGHT that work, the digging of flowerbeds,say, or the hauling of nets through the surf, is valuable in itself, and not just as a means to get something (flowers, fish) is what Matthiessen is really talking about in both books. With Zen, he is attempting to learn a discipline; with the disappearing fishermen of Long Island, he is celebrating a discipline now almost lost.

No one knows when the first nets were laid off the windy tip of Long Island or along that vast beach which stretches from Montauk to the end of the New York City subway line at Coney Island; but all that is left now is a small community of fishermen at Montauk, Amagansett, Springs, and Threemile Harbor, all just east of East Hampton. Matthiessen is their memorialist and advocate.

What's going on in that part of the world is that it has been "discovered." The glitter people have "discovered" the dunes, hardwoods, ponds, etc., and have bought them, leaving little room for the fishermen who have lived there, and their families before, for generations, since about 1660 when the place was settled by a band from the Massachusetts Bay colony. Matthiessen is a queer hybrid, a native to the place himself, yet certainly in any accounting would be considered a rare catch for dinner at one of the Hamptons' summer palaces.

What separates Matthiessen from the chorus of tree-huggers and whale-huggers and literary log-rollers now bewailing everything at the shoreline is that he has spent three years as a commercial fisherman (in the mid-'50s) and has lived the life. The result is that he knows the work, knows the people, and tells the story from their point of view. What gives this story edge is that the netters are considered almost outlaws by "sportsmen" who prefer to use rod and line to catch their "stripers." To the shallow view of summer people and the new squires of Long Island, the sportsmen are in the right, the "commercials" are despoilers.

Matthiessen is one of the American prose poets. He writes with apparent ease the most beautiful, flexible and simple descriptive passages. He is as good at description in his American way as D.H. Lawrence was in his English way. He uses language in its musical realm, and he never gets it wrong when he's talking about the ocean. When he discovers a whale skull in early December it is so: "The beautiful form, crouched like some ancient armored creature in the wash, seemed to await me. No one else was on the beach, which was clean of tracks. There was only the last cold fire of dusk, the white birds fleeing toward the darkness, the frosty foam whirling around the skull, seeking to regather it into the deeps."

But besides beauty, Matthiessen has something important to say. The fishermen he chronicles, like the Zen monks, are men in tune with nature, men who submit to its discipline, men to whom money is less important, and position almost incomprehensible; yet they have secrets -- they are somehow blessed in their lives of hardship, their unceasing routines dictated by nature or custom. They are real, their work is real while we, perhaps, have lost our way. The monks of Zen are obscure, the fishermen are members of an unimportant underclass soon to be pushed aside by designers, architects, decorators and their clients, the important upper middle-class people who own things.

This is Matthiessen's hidden program, to celebrate the people from what he called in Far Tortuga, the "back time." They are the experts: the South Fork fishermen, for instance, who probably know more than the ecologists and scientists who study (and are baffled by) the striped bass, the Zen scholars who are seeking enlightenment in the dark before dawn.

And others who, knowingly or not, bow to Matthiessen's dictum (from Dragon River) that "The absurdity of a life that may well end before one understands it does not relieve one of the duty . . . to live it through as bravely and as generously as possible."

Duncan Spencer, the author of "Conversations With the Enemy: The Story of Pfc Robert Garwood," is at work on a study of social elites in Boston. CAPTION: Picture 1. no caption, FROM MEN'S LIVES; Picture 2, no caption, PHOTOGRAPH BY DANNY LYON FROM MEN'S LIVES;Picture 3, Peter Matthiessen,(c) BY HANS TENNSMA