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He raised the money, overcame innumerable practical obstacles right down to the cutting of the long balsa logs he needed, recruited five friends to go with him and set off on the Kon-Tiki.

Mr. Heyerdahl's book ''Kon-Tiki'' was praised by Lewis Gannett in The New York Herald Tribune as ''a superb adventure story.'' Harry Gilroy, in The New York Times, wrote: ''Their saga, told by the expedition's organizer, is a revelation of how exciting science can become when it inspires a man with the heart of a Leif Ericsson and the merry story-telling gift of an Ernie Pyle.''

The book was less successful with the scientific community. In 1958, for example, Dr. Alan S. C. Ross, a linguist at the University of Birmingham in England said language studies provided ''an absolutely decisive disproof'' of Mr. Heyerdahl's theory. There was, Dr. Ross wrote, no relationship between Polynesian and any American language family.

Mr. Heyerdahl insisted, however, that in his mind he had proved his thesis -- not that the crossing had been done, but that it could have been done.

Next, Mr. Heyerdahl led an archaeological expedition in 1953 to the Galápagos Islands, 700 miles off the coast of Ecuador. He found evidence that convinced him that predecessors of the Incas had visited the islands, and that they had had the nautical sophistication to be able to return home against the wind.

In 1955 and 1956, Mr. Heyerdahl tackled the mystery of remote Easter Island. He experimented with the techniques that might have been used in creating and placing upright the enormous stone figures for which the island is famous. ''Aku-Aku,'' published in 1958, was a vivid account of the expedition. He later published scholarly accounts of this and the Kon-Tiki voyages.

Mr. Heyerdahl argued that Easter Island was also colonized by South Americans, which led one critic, the British archaeologist Paul G. Bahn, to write, ''It is unfortunate that he has allowed his obsession with a South American connection to overshadow the far more interesting and important subjects of the islanders' cultural history, way of life and destruction of their environment.''

Mr. Heyerdahl then turned his attention to the possibility of a migration from Egypt to America, because of what he felt were striking cultural parallels, notably pyramid building. Most scholars doubted that the Egyptians had ships capable of so long a voyage. So Mr. Heyerdahl decided on a practical demonstration. Using ancient representations of Egyptian reed boats as his guide, he had a reed ship built and named it Ra, after the Egyptian Sun god.

The first attempt, in 1969, fell short. The waterlogged ship had to be abandoned 600 miles from its destination in Barbados. Undaunted, Mr. Heyerdahl tried again the next year. He said it was on this successful 57-day journey, on Ra II, that he first noted the ''alarming'' pollution of the ocean, a subject he continued to raise forcefully.

Political strife shortened his 1977-78 voyage with another reed boat in the Indian Ocean and Red Sea. Reaching the coast of Ethiopia, he was refused permission to land because of warfare. He then abandoned the voyage, setting fire to the boat ''to protest against the inhuman elements of the world of 1978.''

With these expeditions, Mr. Heyerdahl said: ''I have proved that all the ancient pre-European civilizations could have intercommunicated across oceans with the primitive vessels they had at their disposal. I feel that the burden of proof now rests with those who claim the oceans were necessarily a factor in isolating civilizations.''

Most anthropologists think otherwise.

Mr. Heyerdahl's first wife, whom he divorced in 1949, died in 1969. He was also divorced from his second wife, Yvonne Dedekam-Simonsen Heyerdahl, who survives. In 1996, he married Jacqueline Beer Heyerdahl, a French-born Hollywood actress, who also survives.

Other survivors, besides his son Thor, of Lillehammer, Norway, are another son, Bjorn, who lives near Allassio, Italy; two daughters, Marian and Helene Elisabeth, both of Oslo; seven grandchildren and six great-grandchildren.

In recent years, Mr. Heyerdahl received many honors, including the distinction, according to a public opinion poll, of being ''Norwegian of the Century.'' And in recent months, he visited Cuba and Norway, as well as Samoa. He sponsored excavations in southern Russia in search of artifacts to support his last obsession, that Odin was a historical personage from what is now Russia who began a Scandinavian royal line in the first century A.D.

As with his theory on the peopling of the Pacific, his case for Odin has been largely dismissed by establishment academics, but as always, he seemed to thrive in the limelight of controversy and the telling of a good story.

Photos: Thor Heyerdahl personally tested his theory that ancient cultures traveled great distances at sea. In 1970, he reached the New World from Africa on a reed boat. On the raft Kon-Tiki, in the Pacific, he subdued a shark. (Photographs by Associated Press) Map of North America, South America and Africa highlighting Heyerdahl's journey: In 1947, Thor Heyerdahl left Peru on the Kon-Tiki and landed on an island near Tahiti. Later, he reached Barbados on the Ra II, a reed boat.