COLUMN ONE : Walking Over Top of the World : Italian adventurer Reinhold Messner has conquered Mt. Everest and the South Pole. At 50, he has set himself a last, great challenge--to be the first to make the icy trek from Asia to Canada.

MERANO, Italy —  There are four toes in his boots, white flecks in his beard and 50 years riding on his shoulders. In Reinhold Messner’s reflective mind, determination jostles with intimations of mortality.

The aw-shucks Italian daredevil who is generally recognized as history’s greatest mountain climber is embarking on his last great expedition and perhaps his most daunting challenge--an ice cap stroll, Asia to America.

Messner will leave this week for a 1,200-mile walk across the frozen Arctic Ocean from Siberia to Canada via the North Pole. Weather permitting, he expects to start walking next Wednesday and to arrive 90 days later.

It has never been done, this across-hemispheres, over-the-pole trek at 40 below. Moreover, there is compelling testimony to say that it is impossible.

What better rite of spring for a self-testing, limits-defying, middle-aged explorer with a restless 12-year-old locked up inside him? As much as anyone in the world today, it is Messner who embodies the old-as-humanity “because it’s there” spirit of discovery.

“It’s the only thing I know how to do. It’s too late now at my age to stop, not to do it. And more than anything--I’m like a child--I would always be unhappy if I don’t try,” he said in an interview at his winter home here in the mountains of Italy.

As he aims once again for the record books where his feats already are deeply etched, Messner portrays himself as the last of a breed and the first of a new breed. He is the explorer as anti-macho man, the man of action who is humbled--even frightened--by the wilderness he challenges.

“I have never had the sensation after a great expedition or a climbing expedition or a great adventure that I had conquered, that I had been stronger than nature. We are always the weaker. Luckily, we have the intelligence to survive. We have fear too, which tells us when not to go ahead. I see fear as a positive thing; it’s a trick to help us survive,” he said at his handsome apartment in this old spa center in the South Tyrol, the German-speaking province that Italy wrested from Austria after World War I.

Messner is a master at wringing that extra drop from extremis. New Zealand’s Edmund P. Hillary wore an oxygen mask and was backed by seasoned mountaineers and foot-sure Sherpas in 1953 when he became the first to conquer Mt. Everest. Messner, solitary as an eagle, was the first to climb the world’s highest mountain without an oxygen supply, and alone. He is the only one who has climbed the world’s 14 peaks higher than 26,247 feet (8,000 meters). And he has walked polar ice before--to the South Pole in 1990, and diagonally across Greenland in 1993.

When American Robert E. Peary became the first to reach the North Pole in 1909, he took dogs and a battalion of Eskimos to help. Messner’s polar walk will be what he calls a “by fair means” expedition. He will trek with his pediatrician brother, Hubert, each towing a 300-pound supply sled. There will be no dogs, no food caches, no support planes, no outside help, save a once-daily bleat from an American satellite to keep them on course.

With his trademark auburn beard, winsome smile and flair for self-promotion, Messner is one of the most famous of Italians today. He is an elegant, original climber who brought lightning, go-for-it Alpine techniques to Himalayan giants traditionally besieged by heavily laden, slow-motion expeditions.

Messner turned 50 in September and says there are days when he feels it. “Jogging yesterday, I felt a twinge in my leg; 10 years ago I could run for five hours and hardly know it,” he said recently.

For him, 50 is not a peak but an improbable plateau. He knows that he is lucky to have lived so long.

“One night in the Antarctic, the wind was so bad if the tent had gone I knew we were finished. In the Arctic it will be cold, but without the fierce wind. If we get a blizzard, we’ll simply stay in the tent,” he said.

Messner has made a career of close calls. At 25, an indifferent student of architecture at the University of Padua, he scaled his first 26,000-foot mountain, Nanga Parbat, in Pakistan. He lost a brother, Gunther, to an avalanche as they descended from that summit. He lost six toes to frostbite in a frantic search for his brother, who was never found. That was in 1970.

Messner wondered if he would ever climb again.

He did--with tragic results: Two friends in his party died on Nepal’s 26,760-foot Manaslu in 1972.

And he climbed with revolutionary impact: In 1975, Messner breached the northwest face of 26,470-foot Gasherbrum in Pakistan the Alpine way, with a burst to the peak from a camp at 18,000 feet.

In 1978, he returned to Nanga Parbat, where his brother lies, and became the first to climb it alone. That year, he and Peter Habeler became the first to climb 29,028-foot Everest without oxygen. In 1979, he climbed the world’s second-highest mountain, 28,250-foot K2 (Godwin Austen), in Pakistan, again without oxygen. And in 1980 he made his solitary conquest of Everest.

Today, Messner is a familiar face in Alpine Europe, advertising chocolate, mineral water and apples on television and in magazines. All of this helps to finance his expeditions and restoration of the 12th-Century castle where he lives in the summer and runs a restaurant serving home-grown produce. Outdoor clothing designers pay him to wear their all-weather products; manufacturers want him to drive their off-road cars. For $20, he will send you a card postmarked from the North Pole. He has a German sponsor and an Italian sponsor for his pole walk. Messner is well-to-do, although not in the same league as American professional athletes.

But it is not money that lures Messner to the Arctic cold at an age when many men only channel surf.

“One goes to live, no? To live a piece of life, to try and see if it’s possible. It’s not necessary to do this, only to try to see if it can be done. This question, ‘Is it possible or not?’ forces someone to try and do it until it’s done. It will be done once, if we succeed. I’d be ready to try two or three times if we don’t,” he said in Italian accented by the German he speaks at home with his Viennese companion and their two small children.

Later this week, Messner and his brother expect to arrive at a Russian military outpost in the Severnaya Zemlya (North Land) islands. The two men’s jumping-off place will be one of the northernmost points of land in Siberia.

From there it is perilous frozen sea to terra firma at Cape Columbia, the northernmost tip of Canada. Peary’s historic expedition departed from Cape Columbia 86 years ago this month.

Messner reckons he can make the walk in 90 days, keeping ever watchful for strength-sapping, dangerous pack ice, potentially fatal water channels undercutting rotten ice, hungry polar bears and frostbite.

“We need good luck with the weather, and with the ice pack,” he said. “The ice pack has to be quite stable, otherwise. . . . But we’ll try. If we survive the first 20 days and manage to do 200 kilometers (about 125 miles), I think we can do it. After that we’ll go much faster.”

Norwegian explorer Boerge Ousland thinks he is wrong. That troubles Messner and pushes him. Last year, Ousland, 31, a North Sea diver, became the first to walk to the North Pole alone and unaided. It took him 52 days with a sled weighing about 290 pounds. Anything heavier would have been impossible to handle, Ousland says of an expedition on which he lost 22 pounds.

Maneuvering the sled across pack ice--with its boulders, blocks and ridges of ice jumbled together and its taller-than-an-explorer obstacles--nearly beat Ousland. “The pack ice saps your strength. It’s just a question of not giving up,” he writes in a new book. Once the hardy Norwegian reached the Pole, craving lasagna and a shower, a plane flew him out in triumph.

For Messner’s planned walk all the way to Canada, which is expected to take 38 more days and hundreds more exhausting miles, sled and supplies will weigh 330 to 350 pounds: his tent, sleeping bags, skis, medical supplies, pencil and paper for the expedition journal “and a Winchester just like Clint Eastwood’s, for bears we cannot scare away.”

Each brother will have 90 frozen 2.2-pound packs of pemmican (dried beef and lard) and enough kerosene to cook with and to make water and coffee--the expedition’s only luxury. One sophisticated hand-held marvel will receive a satellite signal to tell Messner where he is; another will send a signal enabling two satellites to relay his position to a receiver in France.

In what amounts to calling home, Messner will activate one of 15 preset signals to the satellites each day: “Five means we’re fine, six means the bear is getting closer, that sort of thing,” he jokes.

The trek will mark what Messner calls his third pole: Everest, South, North. It is a labor of love at once sobering and uplifting, he says.

Indeed, the new adventure, five years in the planning, epitomizes Messner’s view of his craft, and his ideals: “If you go out in the South Pole you’re really lost and small and weak before great problems. You move slowly, step by step, trying not to fall or make a mistake, but you’re very happy every evening that you have survived, and that’s wonderful.”

It is the shrinking of a wilderness that has challenged and succored him that preoccupies Messner as he sets forth on a walk he says will be physically tougher than climbing a 26,000-foot mountain.

“At the beginning of this century, the desire was born--and I am the last son of these pioneers--to conquer the last blank spaces on the globe. It became a race: South Pole, North Pole, Everest. We always said, ‘We are going to conquer for humanity,’ even if there’s nothing there. And that’s what we’ve done.

“I am the prototype in the last 20 years of the kind of man who helped conquer the blank spaces,” Messner mused. About 10 years ago, he says, his view of the wilderness changed. “I don’t want to conquer the last blank spaces anymore,” he said. “I want to defend them.”

Messner says he is appalled at the degradation of areas scarcely ever seen a few decades ago, such as the climbers’ refuse he found strewn across high mountains such as Argentina’s 22,834-foot Aconcagua. He is equally alarmed at plans to build a refuge 17,700 feet high on Everest.

“The mountain has become something no longer real. It’s like a picture postcard for most people. It’s not something large, dangerous, fearful; it’s become something beautiful where you do sport, like in a gym.”

Wilderness areas are a gift, Messner says. They should stay wild.

“Yes, we have the right to go there, but we haven’t got the right to change anything,” he said.

It is time, Messner believes, to stop installing creature comforts in remote areas whose future is then mortgaged by them.

“The only filter to keep out too many people is the difficulties, the location and the danger. These must all remain. Whoever comes, OK, but whoever doesn’t come because the path isn’t there, because there’s no refuge hut, because they have to carry their own provisions, doesn’t come.”

There is a fundamental truth that Messner says he has learned on mountain climbs and walks across desert sands and Arctic tundra: “Tranquillity arrives only where the road ends.”

By Reinhold Messner’s standards, then, it should be a peaceful walk. There are no roads in the emptiness between Siberia and Canada, just the endless ice and a pensive pathfinder’s burning desire to have crossed it.