ANTHROPOLOGISTS have long been attracted to South Pacific islands for more than the warm breezes and sparkling lagoons. They go to such places seeking in the simpler societies the rudiments of human community, sometimes glimpsing a rough-hewn harmony beyond the experience of more complex societies.

So it was for Dr. Maria Lepowsky, who in 1978 became the first and only anthropologist to live with the people of Sudest Island -- or to use the local name, Vanatinai, meaning motherland. This is a sparsely populated island in the Louisiade Archipelago of Papua New Guinea, which extends southeast of New Guinea and separates the Solomon and the Coral seas. The people there are an anthropologist's dream because they have had only minimal contact with Western colonialism and missionaries.

The longer Dr. Lepowsky observed the people, sharing their daily lives for two years and learning their rituals and ideologies, the more she realized that life on Vanatinai was different from other societies in one fundamental respect. Men and women were living and working as virtual equals. This was, she concluded, a striking example of what anthropologists call a gender-egalitarian culture, and perhaps the first one to be studied in detail by any anthropologist.

"It is not a place where men and women live in perfect harmony and where the privileges and burdens of both sexes are exactly equal," Dr. Lepowsky said, "but it comes close."

Close enough, she said, to challenge the position of some theorists in anthropology that male dominance is universal or somehow inherent in human cultures and that only its forms and intensity vary. The new findings suggest instead that the island's culture could serve as a model of what a sex-egalitarian society would be like and a countermodel to relations between the sexes and ideologies in nearly all other cultures.

Dr. Lepowsky began the research while a doctoral student at the University of California at Berkeley and has elaborated on the findings in a book, "Fruit of the Motherland: Gender in an Egalitarian Society," published last month by the Columbia University Press. She is an associate professor of anthropology at the University of Wisconsin at Madison.

Other anthropologists said the Vanatinai study was certain to draw new attention to the role of a person's sex in the complex interrelations of individuals and society. It could influence scholars to search for other cultures, mainly small-scale groups in the South Pacific and Southeast Asia, that may also be verging on sex egalitarianism.

Dr. Sherry Ortner, an anthropologist at the University of Michigan at Ann Arbor, said such findings might have provoked stormy ideological debate two decades ago, when the supposed universality of male dominance and female oppression was politically charged dogma to many anthropologists. "It's not so radical now to say that some societies may approach egalitarianism," she said. "Most debate now would be over different definitions of equality." Problems of Definition

Dr. Christopher Boehm, director of the Jane Goodall Research Center at the University of Southern California in Los Angeles, who has studied egalitarian behavior, said the quest for a truly equal society had often run into problems of definition. "It's very difficult to know if women and men in another society have equal power and wealth," he said, "since our definitions of power and wealth are themselves culturally biased."

In praising the work of Dr. Lepowsky, Dr. Roy Wagner, an anthropologist at the University of Virginia at Charlottesville who is a specialist in cultures of the New Guinea area, said she had wisely confined the book mostly to description of the flow of life in the Vanatinai villages, including evidence for sexual equality in decision-making, ritual practices and property holdings, and refrained from drawing large theoretical conclusions.

Dr. Lepowsky acknowledged that the island's small population of 2,300 and remoteness favored the development and preservation of such a society. On Vanatinai, everyone participates in community decisions, meeting face to face, instead of delegating power to a few leaders, who might tend to be men. Vanatinai has no chief.

Another factor, she said, is that the culture is matrilineal, with kinship traced through the mother's clan and women inheriting and owning land and other property. Other matrilineal societies do not approach equality of the sexes. But on Vanatinai, the central position of women in island life is said to be taubwaragha, which means both "ancient" and "the way of the ancestors."

Dr. Lepowsky found evidence of the equality on every hand. Unlike other Pacific cultures, Vanatinai has no special men's meeting houses or male cult activities. The language is gender-neutral, with no pronouns like he or she. Boys as well as girls care for younger siblings, and men are expected to share in child care as fathers. In many other New Guinea societies, which consider women inferior to men, menstruation is thought of as a form of pollution and menstruating women must go into seclusion, but not on Vanatinai. Women there also have as much sexual freedom as men.