PORT-AU-PRINCE, Haiti (AP) _ Women till the poor land, toil in sweatshops and perform the other drudgery that moves Haiti's meager economy, but the choice of a woman as president in March was their first real taste of power.

''They dominate in agriculture, trade and industry,'' sociologist Daniele Bazin said. ''They, in fact, run this country.''

Until Ertha Pascal-Trouillot, 46, was installed March 26, women were virtually excluded from power in Haiti, which has been ruled by dictators through much of its 186 years.

As recently as the early 1980s, women were regarded as ''legal minors,'' barred from opening bank accounts, buying property or traveling without the consent of their husbands.

Those laws have been repealed, but little has been done to improve the hard lot of most Haitian women.

Mrs. Pascal-Trouillot, the only woman ever to serve on the Supreme Court, has become a symbol of women's aspirations since taking office as provisional president.

''I accept in the name of Haitian women,'' she said at the inauguration.

Her civilian administration, which is to govern as caretaker until democratic elections can be held, replaced the 18-month-old military government of Lt. Gen. Prosper Avril, who was driven into exile by a popular uprising.

The choice of Mrs. Pascal-Trouillot by a coalition of opposition groups ''had psychological impact,'' historian Suzy Castor said.

''When the army gives up power to a civilian, and to a woman at that, it has a lot of meaning,'' she said. ''I don't have illusions, but it represents a few steps.''

Symbol she may be, but the elegant, highly educated president has little in common with her illiterate, improverished sisters.

Women from privileged families have gained ground in Haiti - about half the doctors are women, for instance - but only one-fourth of university students are women. What money is available for higher education usually goes to a son.

Haiti, which shares the island of Hispaniola with the Dominican Republic, is the Western Hemisphere's poorest nation.

Most of its 6 million people live in the countryside, working tiny mountain plots of coffee, sugar cane, rice and corn with primitive tools. Agriculture accounts for 32 percent of a gross national product valued at $1.5 billion annually.

Half the work force is unemployed and average annual pay for those who find jobs is only about $370. Most city dwellers live in slums without electricity, potable water or adequate sewers, and life expectancy is 53 years.

The 8,300-member army is a way out of poverty for men. Women run the households, care for the children and support the economy in countless ways.

Most of the distribution and sale of crops is carried out by peasant women who walk long distances in the mountains to sell their goods at outdoor markets.

Women called ''Madames Sara,'' for a migratory bird, handle most of the trade with the rest of the Caribbean, traveling to the Dominican Republic, Puerto Rico, Martinique, Curacao, and Panama to buy kitchenware, shoes and food for sale at home.

Government tax incentives and low wages attract foreign-owned manufacturing plants that produce electronics, clothing and sporting goods for sale abroad, mostly in the United States. Women make up about 75 percent of the factory workers, who are paid only $3.20 a day.

Paul Latortue, a Haitian economist at the University of Puerto Rico, said women's conomic contribution is ''overwhelming.''

''Though we don't have the data, I believe women produce the better part of Haiti's GNP,'' he said.

About 80 percent of Haitian mothers raise their children alone. Marriage is commonly viewed as a preserve of the upper class and most children are born out of wedlock.

Couples who live together consider themselves married, but men have no legal obligation to pay child support or alimony. Men change wives at will and may have several at the same time.

''Men run around a lot to prove their virility,'' said Irene, a 22-year-old housemaid who asked that only her first name be used.

Claudette Werleigh, social affairs minister and the Cabinet's only woman, said men often have several ''wives'' in a lifetime.

''Among the poor, the man has many women, so he is absent,'' she said. ''He escapes the problems, the sick children, the crying.''

Haiti has an infant mortality rate of 135 per 1,000 births, highest among Western nations, and women tend to have several children so a few will survive. Children are a woman's protection when the man leaves, and often go to work when very young.

''The only thing a woman has to look forward to in Haiti is that her children will have a better life than she does,'' said Mrs. Bazin, the sociologist. ''They are her insurance policy, and she will slave so her child can get an education.''

Violence against women is common, but usually goes unreported because abused women have nowhere to turn.

''There are no women's shelters,'' said Lilian Pierre-Paul, a popular radio newscaster. ''When they are beaten they come here. They come on foot, in trucks, to talk to me and ask for help.''

Feminists say attempts to organize have been difficult because Haitian women's priority is economic survival. ''Women don't have time to go to meetings,'' said Michele de Ronceray, a sociologist and political activist.

Women's groups have sprung up in recent years, however, and some observers see Mrs. Pascal-Trouillot's government as a turning point.

''We go the countryside and women are saying they are concerned about their lives,'' said Daniele Fouchard, founder of am education and health center for illiterate women and children that has 300 branches.

''For years, they weren't able to say what they were thinking; they were afraid to talk,'' she said. ''People are thinking something can change with a new person, with a woman as president.''