Imagine that you are moored on a small cruise ship in still, black water, in a cove surrounded by tall spruce trees. Beyond the inlet are mountains, brown-black and remote, their sides streaked with snow. It is twilight, and the silence of night sounds is broken only by a delicate ''whoosh'' and a faint rippling of water.
A few yards away, an eagle glides on eight-foot wings, scanning the water. Suddenly it dives, breaking the glossy surface with pale yellow feet - and, as suddenly, flies up again, with a silver fish dripping from its talons.
The quiet of the cove is filled with the swift efficiency of eagles. Every tree has a bright spot of white - an intense head, watching. They fish all night , in the continuing twilight of Alaska.
Admiralty Island is known for its nesting bald eagles, and Alaska has more bald eagles than the whole of the rest of the United States combined. The ship is the Majestic Explorer, chartered for this cruise by Special Expeditions. Its shallow (8-foot) draft enables the ship not only to enter the cove of the eagles , but to travel the intricate waterways of the archipelago known as ''Southeast.''
The cruise is designed to ensure that Alaska does not pass like a film off the port bow. The goal is to bring aboard, in a sense, what exists beyond the railings. Five naturalists are on hand, as well as a captain who knows the water intimately, following his intuitive knowledge of wildlife rather than a rigidly set schedule. There are films by Joel Bennett, a native-wildlife specialist - and Joel himself. There is a library, along with daily summations of geological, zoological, and botanical sightings. And there is extensive time on land.
The landscapes of Southeast Alaska vary widely. Even forests show slight variations one to another - the result of different eras of deglaciation. Humbers (rubber landing craft) take passengers ashore throughout the range - from tidal flats to glacier face.
The ability of the ship to roam into the many and varied small inlets through the whole of ''Southeast'' makes the trip unique. Ferries stick to the middle of the broadest channels. Larger ships cannot get into the shallow, intimate anchorages; even if they could, their greater number of passengers would alter the sense of place. In a kayak or sailboat, you can get a clear picture of any one area - but only one, without unlimited time.
Nowhere else in Alaska is there such an abundance of wildlife. Nowhere else in the world is there the spectacular combination of a major coastal mountain range, great tidewater glaciers, and lush rain forest.
It is wilderness; there are little pockets where man has had some impact, but they're minimal compared with even the most remote sections of the ''lower 48.''
There is only one 15-mile area that can be reached by road, making the region virtually inaccessible except by sea and air - and not even that when the weather is bad.
The feeling of isolation began as we flew into Sitka the first morning of the trip. Below, crisp navy-blue water surrounded the scattering of islands. Sun glinted brightly off the waves but did nothing to warm the austere green of the unbroken spruce forest. Heading for our ship in late afternoon, we walked by a big tub of red snapper and the grizzled old fisherman who had just caught them. Young Indian men moved about on the waterfront, their straight black hair swinging long over plaid shirts and well-worn jeans.
Masts bristled in our wake as we headed out of the harbor into Peril Strait, a channel so narrow that other cruise ships cannot negotiate it. Clouds of gulls swirled around us, brilliant against the slowly darkening mountains. The islands closed in as clouds smudged the mountaintops. At the forest's edge, long sweeps of gray-brown gravel extended out into the water. The water itself changed from hard glittering blue to black.
Abruptly, on an island beside the boat, a bear stood almost in front of us - the great Alaskan brown bear, the ''grizzly.'' It browsed under swags of spruce. We watched in stunned silence. It turned eventually and moved fluidly back into the blackness under the trees.
That we were able to walk on this remote shore was one of the great bonuses of the trip. One of our excursions, five days later, took us to a picnic in a fjord. We sat between steep green walls, a waterfall drifting down the cliff opposite, its spray gleaming in the sun. Some passengers explored the rich tidal pools; others watched a frieze of harlequin ducks basking and dipping around a spit just yards away.
I followed the pull of the forest. Past the perimeter of dense alder thickets was an expanse of muted light, with a foot-thick blanket of moss covering the stream, boulders, and huge fallen trees. As I entered, I passed grizzly hairs stuck in the moist sap dripping from a tree.
Most passengers preferred the grassy slope with hamburgers and homemade potato salad. Before them, icebergs floated silently on the tide.
The picnic spot is called Ford's Terror, after an earlier traveler who sailed peacefully up the fjord against the tide but was caught, as the tide changed, in a raging turbulence of whirlpools and racing icebergs. The name is typical of a literal quality about Alaska. Alaska is wilderness - in a much more profound sense than is conveyed by the now legendary moose on an Anchorage runway delaying a London-Tokyo jet. That kind of public relations blurb simply attempts to bring the vastness of the wilderness within comprehension.
To experience wilderness, it is vital to be aware that just beyond the electricity and the ship are conditions that are unforgiving, that are totally unshaped by man. Wilderness can put a nine-foot grizzly in your path and send huge chunks sliding down from the face of a glacier, spraying pieces of ice like shrapnel. But on this trip, when you're filled to the brim with wildness, you can come inside for a cup of hot chocolate and a warm seat by the window.
The ship also lets you take advantage of the long Alaska day. You can sleep whenever you want - watching sunset, night, and sunrise follow each other in a disorientingly rapid succession.
On the Majestic Explorer, the number of passengers is limited to 72, a contrast to other cruise ships with itineraries in Alaska's Southeast. Some have passenger loads averaging 10 times that. That is why this cruise can be so flexible.
Also, on this small ship, you are close to the water. Often I hung far out over the bow watching Dall porpoises speed in front of the ship, entranced by sleek black and white, by the grace as they sliced dorsal fins cleanly up out of the green water.
For almost two hours one day at the entrance of Glacier Bay, the ship followed a pod of 10 to 12 whales. The Fairweather Range rose directly up from the sea in front of us to over 15,000 feet, tissue paper against the peach sky of the long sunset. At first the whales were a routine spotting, everyone peering through binoculars at distant spouts. And then they were all around us - wild animals, but so close to the ship that we looked down at them instead of out. The huge, graceful bodies - sometimes two and three at a time - thrust in flying arcs through the line between water and air.
Transformations between men and animals figure prominently in the mythology of all the coastal Indians. It is clear in their totem poles. Tlingit call the bear ''elder brother,'' and they used to sprinkle eagle down in the traditional gesture of welcome and friendship when a bear was killed for the village.
But birds were paramount. The two clan totems of the Tlingit are the raven and the eagle. Our small, maneuverable ship was able to take us to an extraordinarily large range of birds. We saw kittiwakes nesting on vertical rock in Glacier Bay; Arctic terns diving into water churned up by the ice sliding away from a glacier; long elegant, pelagic cormorants; and tufted puffins whirring their little wings comically to lift plump bodies into the air. I sat one tranquil hour watching a dipper in a steep rocky stream deep in woodland. And I walked among rock sandpipers and oystercatchers on gravel beaches.
But nature is at its most dramatic at the glaciers. Across from Petersburg, I flew over hundreds of square miles of ice and black rock - over the ice field that feeds Le Conte glacier, the southernmost tidewater glacier in North America. This optional ''flight-seeing'' tour provides a glimpse of the bleak and jagged landscape that is behind those dark snow-streaked mountains always circling the horizon. The plane angled down low as the white snow jumbled into the chaos of blue and gray - the blocks of ice that form the icefall at the end of the glacier. As we swept out over the face of Le Conte, ice floes thick below were dotted with seals in their chosen birthing ground.
The next day the ship was shaving through ''rotten pan ice'' to reach the floes clustered at the face of Le Conte. Icebergs clinked eerily against the double hull - intense flat blue and smooth glistening green moving ever so slowly past. I had seen Eliot Porter's photographs of ''jade icebergs'' in Antarctica and thought it could not be. But the fjord was flecked with them and with white ice floes.
Alaska's beauty is one of extremes - from the creaking groans of a glacier to the tiny orchid backlit on a lush forest floor. There isn't much in between.
Henry Gannett wrote in 1902, ''For one Yosemite of California, Alaska has hundreds.'' I thought of him at Misty Fjords National Monument. We awoke there to the quiet muffling of fog, hanging between the green ridges of the mountains, leaving free a few stark silhouetted shapes of tall spruce. We seemed barely to move through the wisps of gray over the glittering backwater, to float suspended in a surreal landscape. The shore was no longer the austere gray of Sitka but lush moss and lichen meeting opulent seaweed at the waterline.
The long, luscious cruise through Misty Fjords and Ford's Terror, and icebreaking to the face of Le Conte, are not standard fare for the traveler in Southeast Alaska. A tour on the Majestic Explorer includes jewels of experience that flow so naturally together that they seem inevitable. They are in fact extraordinary: treasures unearthed by dint of hard work.
Such a treasure is Stan Price. He chops his own wood at age 86. We visited him in the cabin he built. He has lived for 31 years on Admiralty Island, stronghold of the Alaska brown bear. He has raised several bear cubs and says: ''Anybody raises a bear from a cub, you've got a dog on your hands. Only trouble is, they play rough.'' He protects himself with nothing more than a stick and a conviction of authority. And he has a conviction that the bears have a right to the wilderness. ''We love our bears.'' Stan has been a postmaster and an engineer, has run a mining operation and a sawmill. ''Up here you have to do a lot of things to stay alive.''
But Stan goes on to say: ''I go down to the States. I read the signs and they don't mean much to me. I can't find my way.''
John Muir said something similar: ''To the lover of pure wilderness, Alaska is one of the most wonderful countries in the world.''
The cruise described is operated by Special Expeditions on special charters of the Majestic Explorer. Do not confuse it with regular runs of the ship, which have a completely different and reduced itinerary, more passengers, none of the specialists or special on-shore expeditions - and none of the attention to detail that is synonymous with Special Expeditions and the company with which it is associated, Lindblad Travel.
The cruise, ''Alaska Odyssey,'' is a 12-day trip and costs from $2,550 per person double occupancy. For further information, write Special Expeditions, 133 East 55th Street, New York, N.Y. 10022. Telephone (212) 888-7980.