Undated (AP) _ On the untouched expanse of the Arctic icecap it seemed a mirage - preposterous, incredible: ski tracks.

Will Steger, leading the first unsupported dogsled trek to the North Pole since Adm. Robert Peary's, saw the unmistakable evidence of cross-country skis. He knew they could only be those of Jean-Louis Etienne, a Frenchman who was about to become the first man to ski alone to the pole.

It was in April 1986, in a tent on the monotonous frozen landscape, that the two adventurers sipped tea and dreamed of their next quest: a multinational trek across Antarctica. After reaching their destination, they began planning the Trans-Antarctica Expedition, which is to begin Aug. 1.

Their previous exploits were for the sheer joy of pitting man against nature. This one would do that and more: draw attention to threats against nature and to the need for international cooperation in protecting Antarctica.

Steger and Etienne enlisted scientists and explorers from the Soviet Union, China, Japan and Great Britain for a seven-month, 4,000-mile trip. Others have crossed Antarctica on snowmobiles and giant snow tractors, but this will be the first unmechanized attempt.

Victor Boyarsky of the Soviet Arctic and Antarctic Research Institute, a popular explorer and veteran of polar travel, is a co-leader. The other members of the team are glaciologist Qin Dahe of China; Geoff Somers, who has spent 42 months in Antarctica with the British Antarctic Survey; and Keizo Funatsu of Japan, a former economist who turned to dog-sledding and adventure.

Somers will plot the trek's course; Funatsu is in charge of the dogs.

Steger, who in the past has picked his own teams, says he is honored that the Soviet Union and China will be sending official representatives. The four members from Western nations are not formally backed by their governments.

Steger recalled that when he asked if Boyarsky spoke English, a Soviet official replied: ''In one year, he will speak English very well.''

''A real interesting diplomatic challenge,'' Steger called it.

Other international support includes the use of China's Great Wall Station on King George Island as a staging point. New Zealanders stationed at the Scott McArdle base donated 12 dogs whose lineage can be traced to dogs owned by polar explorer Richard Byrd. The Soviet Union provided an icebreaker to transport 15 tons of food for the men and 36 dogs; the provisions were cached on the route in November. The USSR also plans to send a military cargo plane to pick up the team from its rendezvous at Steger's Minnesota camp; the U.S. State Department, while not officially sanctioning the trek, is expected to let the plane land.

After refueling in Cuba, the team will fly to the Great Wall Base, about 600 miles south of the tip of South America. The expedition, which will set out in the middle of the Austral winter, will at first follow known landmarks.

''We'll have maps for the first 1,500 miles. The last 2,500 miles there is virtually nothing. It's flat. There's nothing to map,'' Steger said.

They'll cross the Ellsworth Mountains and skirt Mt. Vinson, the continent's highest spot at 16,860 feet. They'll visit three American bases - Palmer, Siple and Amundsen-Scott at the South Pole, where they plan to celebrate Christmas.

The next dot of civilization they'll aim for is the Soviet base at Vostok, near the magnetic south pole. Vostok, the coldest place on Earth, will serve as a base for a French documentary film crew that will travel with the expedition for three weeks, and for the team's pilot.

By March, the trekkers should reach the Soviet base of Mirnyy on the east coast, also known as Queen Mary Coast, ending the longest possible traverse.

They'll be picked up by the expedition ship, built in France with a special aluminum hull designed to pop up and settle intact on top of the ice rather than be trapped and crushed.

So far, about 45 nations have signed television contracts with the expedition. ABC has bought exclusive U.S. TV rights. ''We want the world to know much, much more about Antarctica after our expedition than it did before we set out,'' Steger said.

The continent is roughly the shape of a bottle cap. It rises sharply at the perimeter, then flattens out in a vast, high plateau at an average elevation of 9,500 feet. Antarctica's 5.4 million square miles is more than China and India combined. It has no indigenous people, and wildlife is confined to the coast.

A treaty signed in 1959 by a dozen nations, with additional signatories in subsequent years, put all territorial claims on Antarctica on hold, banned military activity and established freedom of scientific inquiry.

But many countries now have designs on the land for strategic, political and even economic reasons - some expect to find oil, coal and mineral deposits under the ice. Some want to see the continent cut into pie-shaped wedges, but Steger wants the people of the world to demand that it be protected, intact.

''It sounds like a very lofty goal, but Antarctica is a going to play a very important role in the future of the planet,'' he said.

Planetary warming of just a few degrees could melt the polar ice caps, raising sea level and flooding coastal areas, but Steger said it's simplistic to worry about submerged cities. With 85 percent of the planet's fresh water stored in the snow and ice of Antarctica, a thaw would reduce the salinity of the oceans, change ocean currents and wreak havoc with weather patterns.

The other environmental nightmare awakening interest in Antarctica is the discovery of a giant hole in the ozone layer directly over the continent. Ozone screens the planet from excess ultraviolet radiation.

Scientists predict continued ozone depletion will increase skin cancer, but such thinking is ''myopic,'' Steger said. Most significantly, increased solar radiation could disrupt the reproduction cycles of plankton, the microscopic oceanic plants and animals that are the basis of the global food chain.

These ominous changes are most apparent in Antarctica, making it ''like a canary in a mine,'' Steger said.

The team will be under the ozone hole for about 40 days and 500 miles as they cross a 13,000-foot high plateau known as the Area of Inaccessibility. It's the worst possible place on earth for ultraviolet exposure.

The team will carry a monitor and Boyarsky will record ozone levels at regular intervals, the first cross-section of ozone across the continent.

Qin will take snow and ice samples all the way across Antarctica, recording temperatures and oxygen content for a geological history of the icecap.

Etienne, a physician, will monitor cholesterol levels of the team members, who will rely on the high-fat diet typical of cultures in cold regions.

But the experiments that can be done along the way are limited by time and weight. The trekkers plan to travel 30 miles a day on cross-country skis, and the three dogsleds can carry no more than 900 pounds of gear.

Steger admits they won't attempt ''pure science'' but he hopes the findings will contribute to the knowledge of this frontier. ''We need international cooperation. Solutions to environmental problems must be global.''