Nicaraguans cast ballots Sunday to decide whether Sandinista leader Daniel Ortega will return to power in a race closely watched by the United States, which backed the war to try to overthrow him in the 1980s.

The U.S. has warned against an Ortega win, with Commerce Secretary Carlos Gutierrez saying aid and trade "will be endangered" if "anti-democratic forces prevail." The race is also key for Venezuelan President Hugo Chavez, a U.S. opponent who is hoping to find a new ally in Ortega.

While some polls opened late, few major problems were reported. Pablo Ayon, head of the independent Nicaraguan Civic Group for Ethics and Transparency, said participation was "high, orderly and peaceful."

Amid fears of fraud, the vote is being monitored by 18,000 electoral observers — including three former presidents: the United States' Jimmy Carter, Peru's Alejandro Toledo and Panama's Nicolas Ardito Barletta. Armed soldiers guard polling stations, while the independent Nicaraguan nonprofit agency Civic Group for Ethics and Transparency is carrying out a quick count of votes.

In a veiled reference to the United States and Venezuela, Toledo condemned "any interference, wherever it comes from, whether it be Asia, Europe, North America or Latin America," adding, "Let the citizens of all countries determine their own destiny."

Ortega faces four opponents: Harvard-educated Eduardo Montealegre, Sandinista dissident Edmundo Jarquin, ruling party lawyer Jose Rizo and former Contra rebel Eden Pastora. Most polls show that his closest rival is Montealegre of the Nicaraguan Liberal Alliance, a party that broke from the Constitutionalist Liberal Party of former President Arnoldo Aleman, who was convicted of corruption following his 1997-2002 term.

Both Ortega and Montealegre appeared at a ceremony early Sunday called to begin election day. As soldiers prepared to raise the Nicaraguan flag and the crowd of dignitaries sang the national anthem, a man ran by yelling "Long live Montealegre!" He was escorted out by guards.

The race was Ortega's fifth consecutive presidential campaign. He won a 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.

But Ortega could win in the first round with just 35 percent of the vote if he leads his closest opponent by 5 percentage points. Voters are also electing a new Congress.

Recent polls showed Ortega with a comfortable lead over Montealegre, but just short of the 35 percent needed to avoid a second round.

Ortega cast his vote amid a throng of cameramen, saying he was confident there wouldn't be a runoff. "Nicaragua wins today," he said before climbing into his Mercedes Benz sport utility vehicle and driving away with his wife.

Polls have shown Ortega would have trouble winning a December runoff. While he has a loyal base of support, many voters still have bitter memories of Sandinista rule, which left the country in an economic shambles and saw 30,000 killed in a war against U.S.-backed Contra rebels.

The balding, 60-year-old Ortega has repeatedly said 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 and still uses it as his campaign headquarters. They reconciled after Ortega offered to pay Morales for his former home.

Marvin Lopez, a 46-year-old doctor waiting in a long line to vote at the polling station where Ortega was also casting his ballot, said he feared an Ortega win 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.

At the end of the line was 26-year-old student Gema Amaya Larios, who said she woke 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 last five years in office, from 1985-1990.

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

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