TWENTY-SIX YEARS AFTER the first ascent of Everest, Sir Edmund Hillary is still the world's most famous mountaineer.The circumstances that conspired on May 29, 1953 to place him, with Tenzing Norgay, on the summit of the highest mountain on earth had less to do with climbing ability than with the quirks of high-altitude conditioning and expedition logistics. As Hillary would be the first to acknowledge, any of a hundred other mountaineers of his day might just as easily have reached the top first.

The effect of Everest, however, was to convert a shy New Zealand beekeeper into an international hero and curiosity. Under the onslaught of commercial offers, Hillary might well have descended into the self-parody of an aging Buffalo Bill. To his credit, he has used his fame-despite Wild-West-Show-ish seductions like a lifelong sinecure as a "consultant" to Sears-simply to pursue what all mountaineers dream of: a life filled with exotic voyages. Surely no explorer has ever handled a comparable celebrity with such unaffected bonhomie.

Hillary's latest adventure, at age 58, is an attempt to go from the mouth of the Ganges to its source by jet boat, with the ascent of two minor peaks near the headwaters to cap it all-thus, a pilgrimage "from the ocean to the sky." Outdoor purists might wince at the idea of jet boats on the holiest of Indian rivers, and indeed, the party themselves worried that the noise of the engines would offend the inhabitants. Unlike other mountaineers, Hillary has no objection to motorized exploring. In 1967 he introduced jet boats to the Himalaya on the Sun Kosi, and his transantarctic expedition with Sir Vivian Fuchs in 1958 was a masterwork of tractor-driving.

Lest the reader assume that taking a jet boat up the Ganges is a piece of cake, Hillary makes clear that such travel requires both nerve and skill. Jet boats must go 30 km./hr. to "plane" out of the water, and running aground at that speed is not only a nuissance but a dangerous jolt. Though remarkably stable in white water, the craft can easily swamp if the bow dips under; boats have been known to flip end over end. Running the rapids of the upper Ganges comes across as a sport legitimately akin to white-water canoeing, and we feel the same admiration for Jon Hamilton, who may be the world's best jet-boat pilot, as we would for a champion kayaker. Far from invincible, the boats are finally stopped cold by a 10-foot waterfall, ending the 1500-mile water-borne excursion-to the mixed regret and relief of the three drivers.

The stamp of all Hillary's writing is the imprint of the man himself. Bluff, ingenuous, incurably enthusiastic, his prose subordinates the personality of the author to an attentive regard for the observed object. The corresponding absence of introspection and of all but the most obvious shades of irony forces Hillary's books to depend on plot. And when the plot lacks focus and intensity, as in the present case, the writing can get a bit dull-travelogue, instead of sustained narrative. Ironically, the expedition's major crisis arises when Hillary comes down with pulmonary edema at a high camp on Nar Parbat, necessitating a sledge-and-helicopter rescue; and here in the book's final chapter, the story at last comes to life.

The greatest hindrance to the expedition, however, comes in the form of the huge throngs that gather at every village all the way up the river-simply to see "Sir Hillary." The fanatic audiences-thousands of Indians cheering wildly at every maneuver of the boats, pressing forward for handshakes and autographs-mean that for months Hillary cannot be alone. His progress up the river becomes a gauntlet of official receptions, speeches and ceremonies. The man's extraordinary good nature finally wears thin , as when he reacts to a journalist wading thigh-deep into the water to photograph him with a telephoto lens from three feet away:

"What was he trying to get? Close-ups of the Hillary teeth? The Hillary tonsils, perhaps? I was sorely tempted to place the size-thirteen Hillary foot in the centre of his abdomen, and give him a quick push into the deep and fast-flowing waters of Mother Ganga behind him."

At times the crowds, through sheer fervor, become truly frightening. Hillary rehearses in his mind the recommended procedure should a barge overrun with admirers happen to tip over: "dive deep; then, before surfacing, swim underwater until our lungs were nearly bursting. This would take us clear of the main mass of passengers, mainly non-swimmers who would grasp at anything afloat."

Because of his fame and because a voyage up the Ganges forms the Indian's dream of the ideal pilgrimage, Hillary and his men take on a virtually supernatural significance in the people's minds. The aura extends even to the boats, which are commonly believed capable of flying; one man swears that he has seen one of them climb a rock wall. Several onlookers ask the party if they are the men who went to the moon. Beseiged by the crowd of 30,000 Bengalis at a refueling stop, Hillary expresses his astonishment to an Indian team member. "'They do not know what they are going to see,' said Harish. 'Some of them think they are going to see Mount Everest itself come down to the river.'" CAPTION: Picture, Sir Edmund Hillary