ATOP CAMELS HUMP --On a clear day from the summit of Camels Hump, the view seems to go on forever. Lake Champlain and the Adirondacks frame the vista to the west in muted blues and greens. To the north, the prow of Mount Mansfield breaks the uneven emerald green swells of the northern Green Mountains.

And far across the Connecticut River valley to the east, a triplet of mountain ranges glint in the sun. After a stiff climb on the Long Trail up the south side of the mountain, such a view seems like a right, not a privilege. As I drink in the view, the brisk northwest wind evaporates my sweat as if I'm being freeze-dried. Pulling on hat and windbreaker, I'm reminded that I owe this gorgeous view to the clear Canadian air riding a cold north wind.

If this were a southwest wind, the mountains would be blotted out by haze. Tiny sulfate particles, spewed into the air from midwestern coal-fired power plants, hitchhike on the southwest wind. When it rains on such days, the rain is as acidic as vinegar.

The Long Trail, Vermont's end-to-end hiking trail, may be a refuge in the wilderness, but the winds that bathe the mountains from the west carry an inescapable message. Whether it's the national problem of acid rain, or more localized problems like water made undrinkable by a tiny parasite, Vermont's most remote places can't escape problems caused by pollution.

It's here on Camels Hump that scientists and environmentalists began a decade long battle to clean up America's air. Studies on the western flanks of the mountain documented the harm dirty air does to an ecosystem. Those studies helped shape national laws regulating pollutants like the ones that cause acid rain.

A summer of rain

My weekend hike begins at Appalachian Gap, high above the ski towns of Warren and Waitsfield to the west and Bristol to the east. For the next two days, I'll be staring at the flanks of Camels Hump as I wind along a rough ridgetop trail. Rain is in the forecast, and in the air as I shoulder my pack and begin a steep climb to my destination for the evening, Cowles Cove Shelter.

Some mountain rains are gentle and misty. Not this rain. It pelts my raincoat as winds buffet the trees. Each time a gust blows, the raindrops shake off the leaves and land on me with a plop. Soon my boots are squishing, but by the time I reach a viewpoint at Molly Stark's Balcony, there's a bit of a view. Ahead is Camels Hump, altered from its familiar crouching lion profile because of my southerly vantage point.

Since the time that Samuel de Champlain's explorers first described the distinctive peak as ''le lion couchant,' the sleeping lion, Camels Hump has drawn the attention of hikers, loggers, conservationists, and scientists. But it wasn't until 1982 that Camels Hump took its place on a national stage, when University of Vermont researcher Hubert Vogelmann described dying trees atop the mountain in the November issue of Natural History Magazine.

''Catastrophe on Camels Hump,'' was one of the first articles written for a non-scientific audience describing how air pollution could actually damage and kill trees. In the 1960s, UVM graduate Tom Sicccama documented the robust health of the red spruce and fir in the high-altitude forests on Camels Hump. Twenty years laters researchers were horrified to find that more than half of those once-thriving red spruce had died. The culprit, they concluded, was acid rain.

The outcry after Vogelmann's report helped spur a major national study on the problem. Congressional politics delayed federal action, but in 1990 Congress approved Clean Air Act amendments to curb pollutants that cause acid rain.

From my vantage point on Molly Stark's Balcony, it's hard to see the damaged and dying trees that now litter the upper flanks of the mountain. Instead, from 10 miles away, the mantle of green wraps like a smooth skirt around the bare rock of the summit cone. But the dead and dying trees are there, I know. Virtually every red spruce I pass on my hike has orange-colored needles - a sign of winter damage, the chief mechanism that actually kills the trees. Acid rain and other pollutants harm trees' ability to prepare properly for the winter. When a cold snap comes, some needles die. If the damage is severe enough, the tree will die.

Solitude, interrupted

I've plenty of time to contemplate the Hump's role in shaping national environmental laws, because I'm hiking alone. One of the things I love best about hiking is its contemplative nature. Being away from the telephone and the distraction of housework gives you time to think. Your body adjusts to the weight and feel of a backpack and finds its rhythm, seemingly without any conscious thought, leaving my mind to wander where it will.

The heavy rain changes that. Even on the best of days, this section of Long Trail is slow going, with lots of ups and downs, and exposed, sheer rock that demands delicate maneuvering with a pack. I'm definitely much more careful than I would be with a companion. Alone, if I fall, I've only my own resources to rely on. And in the pouring rain, I know I don't stand much of a chance of meeting any other hikers.

I pull into Cowles Cove shelter just before dinnertime. It's empty, and in the humid air there's a faint aroma of wood smoke. I'm so wet my feet squish in my boots and I wring a cup of water out of each sock. A few bubbles are just beginning to rise from a pot of water I'm boiling when I see a blaze-orange poncho bobbing in the distance. Company!

Maile Sivert and Jennie Burnet are college friends from Boston University. Maile, 21, is working in Vermont for the summer and Jennie, 24, is about to begin a doctorate program in North Carolina. Their weekend hike is a farewell.

They are traveling light, without a stove. But they have one thing hikers would have never thought to carry 10 years ago - a water filter. The reason is giardia, a tiny water-borne parasite that is found in most streams and rivers in New England. Spread by animal feces as well as by humans, its widespread presence means that all drinking water should be filtered or disinfected.

They are completely matter-of-fact about having to use the filter. I am not so sanguine. I can still remember the pleasure of dunking my face in a cold mountain stream to drink. Now I boil my water to drink and make supper. Their dinner is simple, a loaf of bread with hummus, a chickpea and garlic spread that's protein- rich and delicious. My meal is more traditional -- macaroni and cheese, spruced up with sliced carrots and bits of sun-dried tomatoes.

The evening rain turns to a downpour. When blasts of wind shake nearby trees, it sounds as if someone is dumping buckets of buckshot on the tin roof of the shelter. It's a concert that will last all night.

We three huddle in our sleeping bags. The wet, strong gusts make us feel like we're in a tiny open boat being buffeted by the wind. I make tea; we share.

Sun, and views

We wake to a pale pink sky framed by the black trunks of trees. The sky is a watery blue. The wind remains, but the rain is gone.

We prepare for our day's hike. Maile and Jennie will walk the way I came, to Appalachian Gap, and I will head north to Camels Hump. Over breakfast - hot oatmeal for me, trail mix for Jennie and Maile - we discuss the issue of pollution in the mountains. The pair agree Vermont is probably the most unpolluted place they've been.

''It's beautiful compared to Boston. Walking to work, I used to get dirty just from the air,'' Jennie said. ''I have a hard time considering environmental problems in Vermont because everywhere I've been has been worse than this,'' Maile said. ''I hadn't even considered pollution on Camels Hump.''

As the day unfolds, it's hard to argue with their observation, in spite of what I know. The rain and wind have scrubbed the air squeaky clean, and the views from Burnt Rock, and later Camels Hump, are expansive.

I feel like I deserve them.

Scrambling up Burnt Rock, my first big peak for the day, is tricky with a big backpack. The air is dry, but the rocks are still slick. And the trip up the south side of Camels Hump can be described in only one way - a long grind. The summit is a reward for all my hard work; I've earned the vista. But I know it's luck, and direction of the wind, that has really bought my view.