By Richard Valdmanis and Alphonso Toweh
MONROVIA (Reuters) - Liberians queued peacefully in the rain on Tuesday for the West African state's second presidential election since its civil war, with incumbent Ellen Johnson-Sirleaf bidding for a second term.
The election pits the newly named Nobel peace laureate against former U.N. diplomat Winston Tubman and 14 others.
It comes at what could be a watershed moment for Liberia, with investors ready to sink billions of dollars into its mining sector and the country's potential emergence as an oil nation.
"We've had a difficult past, too hard, but today we are voting for peace," said Monrovia resident Benjaman Nimley as he queued with others to cast his vote at a high school converted into a polling station in the seaside capital.
Pointing skywards to the latest downpour of the steamy rainy season, he added: "It is the rain that helps you appreciate the sunshine."
Passions have run high in a contest some forecast will go to a second-round run-off between Johnson-Sirleaf and Tubman.
Many voters recall how a dispute over the outcome of the 2005 election led to days of rioting in the capital Monrovia. But observers said the vote so far had been peaceful.
"So far so good. The reports that we are getting up to now shows that everything is going smoothly," former Nigerian president General Yakubu Gowon, leading the monitoring team of the US-based Carter Center, told Reuters in Monrovia.
Speciosa Wandira Kazibwe of the African Union observer delegation said: "From what I see there is no worry. If the leaders take the results there will be no chance for violence."
Eight years into peace, Liberia has seen growing investment in its iron and gold mines and has convinced donors to waive most of its debt, though many residents complain of a lack of basic services, high food prices, rampant crime and corruption.
"Ellen done nothing, I seen nothing," said Anthony, an 18-year-old resident of West Point, a Monrovia slum where raw sewage trickles between a crush of makeshift brick and tin dwellings, home to many of the civil war's ex-child soldiers.
Unemployment remains high, war-wounded beg on the streets and average income stands at $300 a year -- below the $1-a-day benchmark for extreme poverty.
Johnson-Sirleaf initially ruled out a second term, but has since said she needs one given the huge challenge. Her jocular campaign slogan -- "Monkey Still Working, Baboon Wait Small" -- urges Liberians to have a bit more patience.
"DIFFICULT TO GOVERN"
Campaigning for the election has been mostly calm, though scuffles erupted between rival supporters in Monrovia during final rallies at the weekend.
The election will be Liberia's first locally organized presidential poll since the end of the 1989-2003 conflict that killed nearly a quarter of a million people. Johnson-Sirleaf became Africa's first freely elected female head of state in the 2005 election that was organized by the United Nations.
Tubman, whose running mate is ex-soccer star George Weah, is expected to give Johnson-Sirleaf her toughest challenge.
Analysts say Johnson-Sirleaf's Nobel Peace Prize, awarded jointly with Liberian activist Leymah Gbowee and Yemeni rights activist Tawakul Karman last week, could give her the edge by galvanizing the female vote in her favor.
A Harvard-educated former adviser to former U.N. Secretary General Kofi Annan, Tubman told Reuters on Saturday he was certain he will win and issued a veiled warning that his supporters could make it "difficult to govern" for anyone else.
Casting his vote on Monday, he said: "I will tell them (the supporters) to accept it if the election is free and fair ... I expect it will be."
Johnson-Sirleaf, voting in her hometown of Fee Fee about two hours drive from the capital, said she was confident she would win. "I am optimistic, I think the Liberian people will do the right thing."
The United Nations said the return of mercenaries from a four-month civil war in Ivory Coast this year could be a threat. Several weapons caches have been seized, but there has been no evidence of plans to disrupt voting.
Citing violent crime, instability in Ivory Coast and trafficking of drug and arms across the region, the U.N. Security Council extended the mandate of the 9,200-strong peacekeeping mission UNMIL last month.
"I hope everybody, as I have appealed and appealed, will proceed peacefully and accept the results according to the rules," Special Representative to the U.N. Secretary General Ellen Margreth Loj told Reuters as she visited a peacekeeper headquarters in the center of Monrovia.
A peaceful, free and fair election could bolster growing investor confidence in the country, which is rich in iron ore deposits and has promising agriculture and energy sectors.
Miners ArcelorMittal and BHP Billiton and oil companies Anadarko, Tullow and Chevron are already active in the country.
The head of Liberia's National Oil Company, Christopher Neyor, predicted an offshore oil find is likely "pretty soon" and said majors Exxon Mobil, France's Total, and Brazil's Petrobras had made inquiries about acreage.
(Editing by Mark John and Giles Elgood)