Whitewater rafting the Tatshenshini and Alsek rivers

Water splashed up and over the boat and into our faces, running in long rivulets off our foul-weather gear. ''Bail!'' called Chuck; and as the raft lurched through deep troughs topped by foaming white, I reached for the bucket.

We were on the Tatshenshini, one of the world's great whitewater rivers, flowing from Canada's Yukon Territory to join the Alsek River in Alaska and empty into Dry Bay just south of Yakutat on the open ocean. The ''big daddy'' of our Alaska Discovery trip was Chuck Horner, the founder of the company. The Tatshenshini-Alsek system remains wilderness in part because commercial travel is strictly limited by National Park Service permits. As a result, you can raft the river without seeing anyone at all.

Our first day we woke to fog, but by the time we set out there was bright sunshine. We moved along in the current with a flock of mergansers; an eagle slowly stretched out his wings as we passed.

The angle of the river steepened, and we picked up speed. Fred Fay-Hiltner, the leader and oarsman of the raft I rode, maneuvered a series of tight, fast turns through a spill of rock. Fred is an Olympics-class kayaker, and watching him reminded me of Henri Cartier-Bresson's description of photography as ''a matter of millimeters.'' At one point we were flying through a churning chute into a canyon toward sheer jagged rock. We swept by, missing it by inches, and plunged into huge waves, towering eight feet over us.

After lunch, we lazed in what Fred calls ''Alaska drifting'' - down through waves only three feet high. Suddenly a bear was thrashing across a stream next to the raft, a sow with her cub running away from us.

Our camp was just ahead in a field of dryas gone to seed. Perhaps the premier Alaska plant, dryas moves in first after glacial retreat to prepare the soil for reforestation. From river to forest edge, the ground was solid with small gossamer balls.

After dinner, Ken Leghorn, another of our oarsmen, said, ''Hey! There's something moving over there.'' He got a blase response; we had had a gourmet repast and were relaxing after the excitement of the canyon. ''A moose,'' said Dick Rice, our third guide. It was visible without binoculars - a light form just across the river. We all went for our binoculars to see it better: ''It's a wolf!''

And it was - a short distance away from us. He gnawed at something, walking around it, tugging. After almost an hour he walked slowly along the shore out of sight.

The river flowed light chalky green our second day, having taken on what is called glacial flour: bedrock which has turned into powder as a glacier grinds down over it. The sun was hot at lunch; so we dove into the river, swimming upstream against the meltwater.

We climbed a bear trail in the afternoon to look out over the land, and saw what looked like a meandering stream curving through the green and the great austere sweeps of gravel.

But by the fourth day, the Tat was a changed river, the bed swollen wide with the volume of water. Mountains rose from the shore.

The river is braided here, and Fred picked our way through the labyrinth, negotiating sometimes in three and a half inches of water. Fine debris churned against the bottom of the raft. We swept nimbly into a small backwater eddy: We are at the confluence of the Tatshenshini and the Alsek.

In the morning, we walked the length of a small tributary stream, climbing 3, 000 feet to an amphitheater of rock and snow. Above is only scree and dirty ice with a thin cap of glittering blue. On the way back down, I saw a bear track superimposed over the morning's imprint of a lug sole.

We passed the next day between the US and Canada; marked by a clearing cut in the trees. The boundary seems artificial here in the wilderness.

And then in the afternoon we walked upon a glacier. We climbed with Ken, an expert mountaineer, up from our camp near the actively calving face, over a large jumble of huge rocks. A black and orange butterfly fluttered by in the reflected heat just yards from the glacial chill. I saw small patches of ice between the rocks and suddenly realized that the boulders dwarfing us were merely flecks of debris on the surface of the massive glacier itself.

Even walking on the glacier's sloping plain, it is difficult to comprehend the amount of compacted ice. Cracks in the surface glow a clear intense blue. Some are deep-carved canyons. Others are rounded pools filled with water. The line of the glacier is unbroken, the transition from white solid to blue liquid indiscernible but for a difference in color.

Back in our raft, we were on the Alsek. This was our one day of drizzle. As we neared Alsek Bay we stopped briefly to walk across a small marshy peninsula: Icebergs floated in the distance, iridescent in the enveloping gray of the fog, just out of reach.

For two nights we camped in Alsek Bay under Mt. Fairweather, watching two glaciers calve and the great chunks drift. Against the backdrop of icebergs, our guides built a bonfire and created a sauna from tarps and sizzling rocks.

On the river again, we stopped to visit Annie Breseman. Half Tlingit and half Norwegian, she lives year-round on the Alsek, alone, setting her nets for salmon. She has twice been wrenched from her boat into the frozen river and pulled under the ice. A white fur is spread on the sofa in her living room; she shot and packed the goat down from the top of the mountain behind her house, walking in hip deep snow. She is the stuff of Alaska legend.

The river banks flatten, where the Alsek flows its last miles to Dry Bay. I had the opportunity to fly over the bay with a local fisherman - like taking a spin in the Chevy to the local take-out. He took me up over the long curves of sand and glacial silt that swirl in baroque patterns, giving the bay its name. In a long golden sunset, the mountains swam in a yellow haze; and the river met the sea. Practical Details:

The 11-day trip costs $1,000 plus $350 for transfer by van to the river and plane charter from Dry Bay to Glacier Bay. The trip leaves from Haines, Alaska, and ends at Glacier Bay. The charter flight is much more than transportation; it is the most spectacular flying experience I had in Alaska - over Lituya Bay, the Brady Ice Field, and the whole of Glacier Bay.

No prior boating experience is necessary. As on all Alaska Discovery trips, the camaraderie extends to sharing camping tasks; and it is an opportunity to learn the skills of minimum-impact camping.

For further information, write Alaska Discovery, PO Box 26-CM, Gustavus, Alaska 99826. Telephone: 907-697-3431.