A group of British explorers attempting the first north-south circumnavigation of the South Pole -- the halfway objective of a three-year trek across land, sea and ice.

The three-man advance team of the amateur Transglobe Expedition arrived at the South Pole last night after a 47-day journey in specially built snowmobiles across 1,100 miles of frozen Antarctica, 900 miles of which had never been explored before.

Despite dangerous deep crevices in the ice, blinding blizzards, accidents and temperatures of 50 degrees below zero, the group, led by Ranulph Fiennes, an author and adventurer, was seven weeks ahead of schedule and in generally good health.

"They really plugged away at it, traveling very long hours each day," said a spokesman at the expedition's headquarters in London. It was notified today by radio via New Zealand of the group's safe arrival at the small U.S. scientific station at the South Pole, which normally is reached by air.

Financed by 300 corporate sponsors -- who donated sophisticated equipment to cope with dangerous terrain and temperature extremes of 120 degrees above zero in the African desert to 120 degrees below in the Arctic and Antarctic -- the expedition set out from London by boat over a year ago.It crossed Europe and the Sahara by Land-Rover and continued to Antarctica on their donated ship.

Five members spent the past southern hemisphere winter 200 miles inside the Antarctic at Ryvingen. Accompanied by Fiennes' dog, Bothy, fthey included Fiennes, who once served in the army of the sultan of Oman; his wife, Virginia; Oliver Shepherd, a former London beer salesman; Charles Burton, a former soldier and businessman; and Simon Grimes, an "outdoor pursuits instructor."

They had trained for the expedition for seven years under the patronage of Prince Charles, who saw them off in September 1979, and with the required approval and sponsorship of the Royal Geographical Society here. In articles written from their lonely Antarctic base camp for one of their corporate sponsors, London's Weekly Observer newspaper, Fiennes answered critics who said the adventurers were inadequately prepared, particularly for the two treacherous polar crossings.

So far, it appears that their snowmobiles and Twin Otter supply aircraft, as well as their own grueling fitness training in the mountains of Wales and the cold of the Arctic have enabled them to cope. The advance party of Fiennes, Shepherd and Burton made the uncharted Antarctic crossing to the South Pole in half the allotted time, mapping the route and performing scientific experiments along the way.

According to the expedition's headquarters here, the three men had to weather "their fair share of storms" and overcome steep ridges grooved deeply into the ice by cutting winds.

Burton was nearly lost when, while lighting a cigarette, he absent-mindedly stepped into one of the snow-disguised, seemingly bottomless crevasses that open up in the ice under the 24-hour sunshine of the Antarctic summer. Only his safety rope made it possible for the others to pull him back to the surface.

Fiennes injured his arm trying to repair a snowmobile after its drive shaft was broken. A replacement snowmobile was flown in by the Twin Otter, which also had been used to rescue three other parties of Antarctic explorers while it was based there for the Transglobe Expedition.

The three men intend to complete their journey across the Antarctic with the relatively shorter and easier trip from the South Pole to another U.S. outpost at McMurdo Sound. Grimes and Virginia Fiennes will be flown from Ryvingen to the South Pole and then to McMurdo Sound, where the expedition's ship will be waiting to take them all to New Zealand.

Much of the rest of the expedition will be by boat across the Pacific Ocean, with trade exhibitions of the donated equipment in New Zealand, Australia, Los Angeles and Vancouver.

The advance team then faces the other major trial of the expedition, traveling to the North Pole by motorized raft up the Yukon and MacKenzie rivers and through the icy 3,000-mile Northwest Passage, and by ski and snowmobile over the Artic icecap.

They are due back in London in August 1982.