Leftist Sandinista leader Daniel Ortega appeared Monday to have easily defeated four other presidential candidates in his long quest to return to power 16 years after a U.S.-backed rebellion helped force him from office, according to a respected electoral observer group projecting victory based on a sampling of the votes.

Ortega's victory, if confirmed by final results, would give Venezuelan President Hugo Chavez a strong ally in the region while threatening U.S. aid to the second-poorest nation in the hemisphere.

News of Ortega's possible victory was met with fireworks and jubilant street parties by his supporters. But many here still have bitter memories of the Sandinistas' decade in power, in which homes and businesses were seized and a war with Contra rebels left 30,000 dead.

The race was Ortega's fifth consecutive presidential campaign. He won an 1984 election boycotted by Sandinista opponents, then lost in 1990 to Violeta Chamorro, ending Sandinista rule and the Contra war. His next two presidential attempts, in 1996 and 2001, were also failures.

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The quick count by the Nicaraguan Civic Group for Ethics and Transparency gave Ortega 38.5 percent of the vote to 29.5 percent for Harvard-educated Eduardo Montealegre of the Nicaraguan Liberal Alliance, a party that broke from the ruling Constitutionalist Liberal Party after former President Arnoldo Aleman was convicted of corruption.

Trailing were Sandinista dissident Edmundo Jarquin, ruling-party candidate Jose Rizo and former Contra rebel Eden Pastora.

The quick count, based on results from a representative sample of polling stations, had a margin of error of 1.7 percentage points. Ortega's four opponents asked the group to carry out the count as a gauge of whether final results were reliable. They had expressed concern that the Supreme Electoral Tribunal was controlled by the Sandinistas and could influence the final vote.

Montealegre brushed aside Ortega's lead, saying: "No one has won here. The Nicaraguan people, in a runoff, will determine the next president." Ruling party spokesman Leonel Teller warned that electoral authorities were "inciting something could end in blood and violence."

Thanks to a change in electoral law, Ortega needs only 35 percent of the vote and an advantage of 5 percentage points over his closest rival to avoid a runoff in December. Before, he would have needed 45 percent to avoid a runoff.

The U.S. Embassy issued a statement late Sunday saying it was too soon to "make an overall judgment on the fairness and transparency of the process."

"We are receiving reports of some anomalies in the electoral process, including the late opening of (polling places), the slowness of the voting process and the premature closing of some" polling places, it said.

Roberto Rivas, president of the Supreme Electoral Council, blasted the U.S. statement, saying, "We have promised the Nicaraguan people transparent elections, and that's what we've done. I think there were enough observers to witness that."

At stake are millions of dollars in potential investments, many from foreign companies drawn to Nicaragua by its cheap labor, low crime rates and decision to join the new Central American Free Trade Agreement. But many businesses are waiting to see if Ortega wins and stays true to promises to continue free trade policies before they decide whether to invest.

"We are playing with the stability of the country," said Jose Adan Aguirre, president of the Chamber of Commerce.

Observers said voting overall was peaceful, although many polling stations opened late, leaving long lines of people waiting to cast their ballots. After the polls closed, groups of angry voters pounded on shuttered doors, screaming at officials inside to let them vote.

Ortega didn't make any public statements early Monday, but he said repeatedly during the campaign that he has changed. In fact, his vice presidential candidate was once one of his biggest enemies: Jaime Morales, who served as the spokesman for the Contras.

As Sandinista leader, Ortega seized Morales' six-bedroom estate, but they reconciled after Ortega offered to pay Morales for his former home -- now Ortega's campaign headquarters.

Marvin Lopez, a 46-year-old doctor waiting in a long line at the same polling station where Ortega voted, said he feared Ortega would bring back uncontrollable inflation and conflict.

"I don't want to return to a dictatorship, the misery, the abuse of families' rights," he said.

Waiting at the end of the line was 26-year-old student Gema Amaya Larios, who said she woke up at dawn to cast her vote for Ortega.

"He's the only one who will give the people what they need," she said. "Everyone else just cares about their own interests."

If Ortega wins, she predicted that his presidency would be different from his 1985-1990 term.

"There was an embargo, a war," she said. "Besides, we all learn from our mistakes."

Armed soldiers kept guard at polling stations monitored by more than 18,000 observers -- including three former presidents: the United States' Jimmy Carter, Peru's Alejandro Toledo and Panama's Nicolas Ardito Barletta.

Nicaraguan presidents cannot serve two consecutive terms, and President Enrique Bolanos steps down Jan. 10.