In June, 1789, a 25-year-old Scot named Alexander Mackenzie led a canoeing party down the river that now bears his name in the Northwest Territories of Canada. Mackenzie, the wintering partner of the fur-trading North-West Company at Fort Chipewyan on Lake Athabasca, was in search of the Northwest Passage to the western end of the American continent and the Northern Pacific.

He found an ocean, but it was the Arctic, 75 miles from the present town of Inuvik.

In June, 1974, two Americans undertook the same journey by canoe that Mackenzie's party had made nearly two centuries before. They started 200 miles south of Fort Chipewyan at Fort McMurray on Alberta's Athabasca River and ended at the Beaufort Sea in the southern Arctic Ocean.

Robert Douglas Mead and his son Jim were alone except on the final leg of their 1,700-mile trip. They paddled the entire way, except for 100 miles portaged by truck from Hay River on Great Slave Lake to a spot just south of Fort Providence at the beginning of the Mackenzie River.

If anyone is capable of such a trip, it would be Mead, who began wilderness canoeing at age 7 with his father in the Minnesota Border Lakes. Luckily, Mead's background also made him capable of telling about the journey in exciting and literate form.

He studied at Princeton and Cambridge, has published short stories, poems and books on a range of subjects and has worked as an editor. He is well known by conoeists for his "The Canoer's Bible" (Doubleday paperback, $2.50) and is working on a book dealing with the people who are laying the Alaska pipeline.

As Mead takes us along the Athabasca River, Lake Athabasca, the Slave River, Great Slave Lake and the Mackenzie River through its East Channel to the Beaufort Sea, he also recounts the Mackenzie story, as taken from the explorer's journal.

The two-centuries-apart journeys did not exactly duplicate - in addition to the different starting points, Mackenzie followed the estern shoreline of Great Slave Lake while the Meads took the shorter west-shore route and Mackenzie followed the Middle Channel of the Mackenzie delta to the sea while the Meads paddled the East Channel.

And, of course, the Meads knew where they were headed.

The Mackenzie party had four canoes. The lead carried the expedition's leader, four French voyageurs from Quebec, the Indian wives of two of them and a German; the second, a supply canoe of Europeans that accompanied the party 300 miles, plus two canoes of Indians. The Mackenzie crew also had to paddle back to Fort Chipewyan. The Meads were content to make it a one-way journey and fly back.

Nevertheless, the Mead trip was strenuous and risky.

Early on, near the aptly named Rapids of the Drowned at the entrance of the Northwest Territories, the Meads nearly became a statistic.While camped during a storm just south of Hay River their canoe got loose; only a pair of logs that had caught the painter saved it. It was one of Mead's most depressing moments. "I knew better," he wrote. "My father never would have left the canoe like that in a storm. But I had done it."

Another mistake in judgment was in joining up with a Canadian identified only as Steve, who made the last few miles from Inuvik to the sea and back again miserable.

On Aug. 9, some 65 days after leaving Fort McMurray, the Mead party reached its destination. The McKenzie group, on a shorter voyage by 200 miles, reached the sea in 39 days.

Despite many stops along the way at small towns and Hudson's Bay Company outposts, the Meads had been pretty much cut off from the outside world. The night before reaching the Arctic, they camped with an Eskimo whaling party. A transistor radio from the tent behind them carried the voice of Richard Nixon announcing that he would resign the presidency. "My God," said Mead, "that means what's his-name's President now! . . . What is his name?"

Along the way Mead finds Indians, Eskimos, priests, traders, bartenders, and wishes he had more time to study the lives and the cultures of the people of the great Northwest. He does perceive enough of the life to whet our appetites.

Perhaps in a future book, after he takes us along the Alaskan pipeline trail.