PORT-AU-PRINCE, HAITI, DEC. 16 -- Free this time from the terror of gunfire and machetes but hindered instead by organizational snafus, Haitians voted today in their third attempt in five years to establish a popularly elected government.

Hundreds of thousands of people sweated in long lines here in the capital, despite fresh memories of a massacre at a polling station that left more than 30 people dead on Nov. 29, 1987 -- the last attempt at a free election.

But ballot shortages, late-opening polling stations and other technical problems were so severe -- especially in the poorest, most crowded slums of the capital -- that initially some observers had begun to question whether the vote would be tainted.

The concerns were sharpened by the fact that the most severe problems occurred in the densely populated, desperately poor ghettos that are the strongholds of the radical Roman Catholic priest who is the apparent favorite, the Rev. Jean-Bertrand Aristide. Of 10 other candidates, only former World Bank official Marc Bazin is given a chance of defeating the priest. If no candidate receives an absolute majority, a runoff is required.

Tonight, foreign monitors who observed vote counts in numerous polling places throughout the capital reported massive majorities of up to 90 percent for Aristide. No results from the rest of the country were available, however.

Pierre Cote, head of an election observer delegation from the Organization of American States, said that despite the delays in start-up, the election "was more efficient than we expected."

The Provisional Electoral Council announced tonight that polls would remain open until all who wished to vote had done so, rather than closing at 6 p.m. as scheduled. Definitive results were not expected until Monday.

At stake is whether Haiti will finally break with the legacy of Francois "Papa Doc" Duvalier and his son, Jean-Claude -- known as "Baby Doc" -- who ruled for 29 years until the latter was ousted Feb. 7, 1986. Since then, military regimes or weak civilian governments have held power. Another presidential election was held in January 1988, but it was controlled by the army and participation was minimal.

More than 700 observers arrived to monitor today's vote in this poorest of Western Hemisphere nations.

The most severe difficulties reported were in Cite Soleil, a sprawling warren of open sewers and shacks that is home to about 150,000 people, many of whom refer to Aristide as a messiah. He was dismissed two years ago by the Salesian order for fomenting class warfare from the pulpit.

All morning, as the sun and the stench rose higher, so did the howls of indignation from the thousands in the streets as the polls failed to open. By noon, few people had been able to vote.

Demonstrators, by turns furious and gleeful, danced through the streets singing, "Hallelujah, Aristide!" They clutched tree cuttings, a symbol of uprooting -- representing the wrenching change that Aristide promises and many Haitians have demanded.

Fueling the ire in Cite Soleil was a rumor that Aristide's place on the ballots had been covered with plastic, making it impossible to vote for him. But reporters could not find such a ballot in the polling stations. Others charged that election officials were supplying pencils rather than pens for voters to mark the ballots.

Turneb Delpe, a candidate for senator in Aristide's party, charged that the confusion was in part a deliberate attempt to subtract from Aristide's vote, but said it would not affect his ultimate victory.

"In 1987, they stopped the elections by violence," he said. "We knew that this year, with all the observers, they couldn't do that. We knew that they'd use these technical ways to stop things."

There were scattered reports of irregularities in the provinces, especially in Cap Haitian, the second-largest city.

Despite the irregularities, no violence was reported. Trucks of policemen and army troops sped through the slums, but no shots were fired. Foreign journalists and elections observers encountered hundreds of voters shrieking their complaints.

Many Haitians said the army, which did nothing to stop the 1987 massacre, had been forced to maintain order by the weight of international pressure.

"We've been crying out for help to the world," said jobless Gabriel St. Vil, 52. "Now we have the assurance of the observers. The foreigners have delivered our freedom."

The voting was peaceful at the school where the Duvalierist thugs opened fire on people in line to cast their ballots in 1987. Former president Jimmy Carter, his wife Rosalynn and U.S. Ambassador Alvin Adams were there this morning to stress the importance of a peaceful outcome this time.

Charles Smith, 26, an unemployed mechanic, waited in line to vote just steps away from where he stood in 1987 when the gunmen opened fire. "I ran outside the wall and I was shot twice in the arm," he recalled, displaying the scars on his left arm.

Smith said he was voting for Aristide because "if Jesus Christ came down to the ground, he would vote for Jean-Bertrand Aristide."

Aristide has many opponents, including businessmen, traditional moderate politicians and former allies of the ousted Duvalier dictatorship.

The point man for the Duvalierists is Roger Lafontant, the former head of the Ton-tons Macoutes, the Duvaliers' militia.

In an interview, Lafontant scoffed at the elections as a "carnival" of errors, "dishonest, fraudulent and partisan" and "an affront to the nation." As interior minister in 1985, he presided over a referendum in which Jean-Claude Duvalier was proclaimed "president for life" with 99.8 percent of the vote. There were no other candidates on the ballot.

Special correspondent J. P. Slavin contributed to this report.

POPULATION: 6.2 million. Most are black with a minority of mixed race and a small number of whites. About 80 percent are Roman Catholic but most also practice voodoo.

GEOGRAPHY: 10,700 square miles. Haiti occupies the western third of the Caribbean island of Hispaniola. The rest is the Dominican Republic. Capital: Port-au-Prince. Population 1.2 million.

ECONOMY: Haiti is the poorest nation in the Western Hemisphere. Per capita GDP was estimated at $375 for 1989, the third consecutive annual decrease.

Two-thirds of the population work in agriculture, forestry and fishing, but only about one-third of the country is arable. Coffee is the main cash crop. Main imports are manufactured goods, machinery, food and live animals.

HISTORY: Colonized by France in the 17th century, Haiti became the first independent black republic in 1804. The United States invaded in 1915 to collect debts and occupied it for 19 years.

The modern history of Haiti is scarred by coup attempts and violent riots. Francois "Papa Doc" Duvalier became president in 1957. He used his ruthless Ton-tons Macoute private militia to crush opposition, and thousands of people fled the country. When he died in 1971, his son Jean-Claude "Baby Doc" took over. He ran a corrupt and repressive regime for 15 years. He fled in 1986, and several attempts since have been made to establish electoral rule.

SOURCE: Reuter