PORT-AU-PRINCE, Haiti (AP) _ The constituent assembly unanimously approved a draft charter weakening the presidency, which enjoyed virtually unlimited powers during the Duvalier regime, and giving official status to the Creole language.

The assembly scheduled a public referendum on the charter for March 29, to be followed by national elections in November and the inauguration in February 1988 of Haiti's first freely elected president in at least three decades.

''This is the first time the Haitian people will really get to decide what kind of government they will have,'' said Guy Latortue, one of the assembly's 60 members. ''This is the first constitution economically and socially in the interest of Haiti's masses.''

The charter would replace constitutions that allowed Francois ''Papa Doc'' Duvalier and later his son, Jean-Claude, to rule virtually by decree for 29 years.

The younger Duvalier fled to France in Feb. 7, 1986, following widespread violent demonstrations against his rule. The Caribbean nation has been governed since then by a three-man military-civilian council.

The assembly was elected last October in voting in which only 5 percent of those eligible took part. But since then, its work in drafting a constitution has been chronicled daily in newspapers and on radio and television, and has won wide public support.

The constitution would divide executive power between the president and a prime minister and provide for election of the president by universal suffrage. The president would be limited to a single five-year term.

The prime minister would be selected by the National Assembly from the political party holding the most seats. Both president and prime minister would participate in the selection of ministers.

The charter also would give increased powers to rural communities and require absentee landowners to work their land or have it confiscated by the state.

Peasants would be encouraged to organize cooperatives and work their land collectively.

Creole, the language of most of Haiti's 6 million people, would be given equal status with French. French, spoken only by the country's elite, had been the only official language.

Hubert De Roncerey, a conservative presidential candidate, says he fears the constitution makes the president little more than a figurehead.

''It is entirely understandable that in reaction to a long period of dictatorship the assembly is attempting to prevent a return to the past,'' De Ronceray said. ''But historically Haitians are used to investing their confidence in a strong leadership.''

Francois Duvalier ruled Haiti from his election in an allegedly fraudulent 1957 balloting until his death in 1971. He dissolved the Senate, banned political parties, turned the Assembly into a rubber stamp for his decrees and declared himself president for life.

Jean-Claude Duvalier took office at age 19 in 1971 after the death of his father, who had lowered the minimum age for president to 18 so his son could succeed him.

The draft constitution raises the minimum age back to 30.

It also eliminates official sanctions against voodoo that had been little enforced. Most Haitians are nominally Catholic but practice voodoo, an African-based animistic religion.

The charter's provisions to decentralize power are intended to reverse the Duvaliers' concentration of political power and economic activity in the capital, Port-au-Prince.

Those policies resulted in massive rural migration to the capital, swelling its population to more than 1 million and making it ''so ... congested that it's almost unliveable,'' says assembly member Louis Roy.

''Under their (Duvaliers') excessive centralization, funds didn't stay in rural towns for their development. Rural ports disappeared,'' Roy said. ''Now that situation should turn around in less than two years.''

Another provision reflecting anti-Duvalier sentiment bars from public office for the next 10 years ''any individual notoriously known to have been a torturer, murderer or embezzler of public funds during the last 30 years.''