Thomas Banyacya, who spent half a century on a tireless and often thankless Hopi spiritual mission to save the planet from the ravages of modern materialism and greed, died on Feb. 6 at a hospital in Keane Canyon, Ariz., about 40 miles from his home in Kykotsmovi on the Hopi reservation. He was 89 and the last of four messengers named by Hopi elders in 1948 to warn the world of impending doom.
The 15,000 or so Hopis are a small nation, but their sense of burden is great. According to a 900-year-old religious tradition, the Great Spirit Maasau'u, Guardian of the Earth, assigned them the duty of preserving the natural balance of the world and entrusted them with a series of ominous prophecies warning of specific threats and providing guidance on how to avoid them.
The prophecies remained a secret oral tradition until 1948, when Hopi religious leaders, alarmed by reports of the atomic bomb's mushroom cloud, which they saw as the destructive ''gourd of ashes'' foretold in the prophecies, appointed Mr. Banyacya and three others as messengers to reveal and interpret the prophecies to the outside world.
Mr. Banyacya seems to have been an obvious choice. At a time when many Hopis were beginning to embrace modern ways, even accepting the governmental jurisdiction of the United States, he had remained so steadfast in his devotion to the sacred traditions and cherished sovereignty of the Hopi that he had spent seven years in jail rather than register for the draft in World War II.
As he tirelessly explained, the Hopi, whose very name means ''peaceful,'' reject fighting in wars, especially for another nation.
(His moral stand apparently had an impact. In 1953, according to Hopi commentators, after writing a letter to President Dwight D. Eisenhower, Mr. Banyacya helped win an understanding with local Selective Service officials that any Hopi who requested classification as a conscientious objector would receive it.)
Mr. Banyacya's special feelings for his culture emerged early. A native of the Hopi village of Moencopi, he attended the Sherman Indian School in Riverside, Calif., where he was so distressed at being required to use the name Jenkins, which his father had accepted, that he later insisted on using his Hopi name.
At the all-Indian Bacone College in Oklahoma, where he was a star long-distance runner, he chafed at the lack of attention to indigenous cultures and helped establish an Indian lodge where students sang and performed traditional ceremonies.
Although his later efforts to persuade the world to respect nature and protect the environment under the threat of a devastating ''purification,'' produced indifferent results, along the way he forged spiritual alliances with indigenous people around the world and was credited with reviving interest among American Indians in their native cultures.
Mr. Banyacya, whose work was supported by donations, traveled widely in the United States and abroad, something that was made a bit tricky by his refusal to apply for an American passport. It was a reflection of his spiritual appeal that he managed to attend several foreign conferences using a Hopi passport encased in buckskin.
Although his appointment as interpreter of the prophecies gave him a broad mandate, from the beginning his main focus was on securing a hearing at the United Nations in accordance with an ancient prophecy to take the Hopi message of peace, as he put it, ''to the Great House of Mica on the Eastern shore where the nations come together to solve world problems without war.''
Although he was often warmly received by United Nations officials, his efforts to give a speech were repeatedly rebuffed. But then, as he explained, the elders had told him to knock on the door four times.
On his fourth attempt, in 1992, he was allowed to make a brief speech at the General Assembly hall, but on a day when the General Assembly was in recess. Only a few delegates were present when he carefully sprinkled cornmeal on the podium and then delivered his message stressing the need for world leaders to listen to those still living in harmony with nature.
A fierce opponent of uranium mining and a variety of other industrial assaults on the environment, Mr. Banyacya warned that an endless quest for material wealth would destroy the balance of the world; yet he did not reject all modern conveniences. His United Nations address and several other messages can be found on the Internet at www.alphacdc.com/banyacya/banyacya.html, a site maintained by the Alpha Institute.
Mr. Banyacya, whose family asked that his survivors not be identified, leaves several children, grandchildren and great-grandchildren.
Photo: Thomas Banyacya (Marcia Keegan, 1984)