THESE are hard times for would-be explorers. If any Stone Age people are left, either Thor Heyerdahl or Jacques Cousteau is probably closing in on their fastness this very moment. The great mountains have all been climbed, many of them without use of oxygen tanks, and ambitious alpinists are reduced to aiming for punctilious distinctions--the first person, say, to solo Changabang without metal equipment of any kind. An infinity of virgin territory lies waiting in outer space, but to get there you must offer up your rugged individualism to a dispiriting military regimen.

Somehow Sir Ranulph Fiennes managed to capitalize on the meager opportunities and register a new, bona fide great adventure: crossing the earth "lengthwise"--from pole to pole. (The idea was originally his wife Ginny's, and throughout the trip her radioside vigils in far-flung places were critical to its success.) No previous explorer had ever counted a double polar coup, and the Antarctic route taken by Transglobe (the expedition's moniker) filled in a 900- mile blank spot on the world's maps.

Lasting from 1979 to 1982 and preceded by four years of planning and practice, Transglobe was a stunning success, especially considering its paltry budget and hand-me-down gear. (Benefactors contributed virtually every pound spent on the venture. And though the trekkers enjoyed sea and air support for tasks like dropping caches of fuel and ferrying canoes, their boat was 30 years old, their plane modest.) Fiennes may dangle too many participles, but his account of the adventure evokes it wonderfully well. In the action passages his writing is often inspired, as when frightened musk oxen thunder off, "their loose fur coats swinging kiltlike."

Except that there were no dwarfs to be foiled or rings to be retrieved, the expedition matched anything in the fantasy sagas. Each pole presented its peculiar hazard. In Antarctica (a continent) it was crevasses, clefts in glaciers that are often hidden by surface snow. The danger was that the expedition's sledges might fall deep down the cracks, taking their drivers with them.

In the Arctic (a sea) the hazard was ice--melting, shifting, tipping, drifting in circumpolar currents. Some of the book's most harrowing passages take Fiennes and his teammate, driving Skidoos (akin to snowmobiles), across abutting floes. When they reached a dead end, they either built an ice-bridge across the gap or backtracked in search of another way. Returning from the North Pole, they deliberately marooned themselves on a xxxto p. 5xxx

xxxfrom p. 5xxx large floe and rode it south for three months to within canoeing distance of the ship awaiting them at the ice pack's edge.

The expedition also had its rivals, notably a Norwegian group on its way to the North Pole at the same time. Though cautioned against racing by the expedition's patron, Prince Charles himself, Fiennes pushed on and relished coming in first: it was the Norwegian Amundsen who outpaced the Englishman Scott to the other pole in 1912.

A descendant of the Norman count who beheaded King Harold at the Battle of Hastings, Fiennes makes light of his baronetcy, and everyone connected with the expedition called him "Ran." Yet the others seemed quickly to fall into the habit of following his orders. Even when the team dwindled to just him and Charles Burton negotiating ice floes in the Arctic, Fiennes made the decisions unchallenged.

How much this deference had to do with the leader's nobility is hard for a democratic outsider to say, but in any case Fiennes had some shrewd observations to make about fellowship on a protracted, cooped-up journey. Of Burton, he writes: "I spent seven long years with him and never got to know him. Strangely enough, I am not convinced that this was a bad thing. The fact that we had never been friends meant that we also needed never fear losing a valued relationship through too much enforced proximity. For success in our venture there was no need for individuals to be friends--just equable companions."

Fiennes takes a swipe at a bickering, failed French expedition for being stacked with experts--"a doctor, a mechanic, a navigator, a radio operator, a scientist or two . . . in short, a nest of prima donnas, likely ingredients for internecine strife" -- and plumps for good old English amateurs like himself. Fair enough in Fiennes' case, but as Roland Huntford demonstrates in his superb Scott and Amundsen, Scott's blithe, uninformed amateurism helped doom his Antarctic quest.

To the Ends of the Earth leaves a great, unanswered question. Transglobe was demanding, perilous, debilitating, and just plain long--all in the extreme. The book dwells on these hardships, and Fiennes and company plainly drew immense satisfaction from overcoming them. But at the risk of sounding frivolous, what I want to know is this: on the whole did they have fun?