* First official results expected Thursday
* Unofficial tally puts Johnson-Sirleaf ahead
* Voting in second poll since war hailed free and fair
By Richard Valdmanis and Alphonso Toweh
MONROVIA, Oct 13 (Reuters) - Liberia is to release a first batch of official results on Thursday from its hotly-contested presidential election, in which Nobel laureate Ellen Johnson-Sirleaf is seeking a second term.
The vote is seen as a test of Liberia's progress since the 1989-2003 civil war killed nearly a quarter of a million people and left infrastructure in ruins. If smooth, the election could pave the way to billions of dollars in investment in Liberia's mining, energy and agriculture sectors.
"We are all waiting for the results, and from my perspective, I think they will be accepted," said Amadou Kante, a resident of the Sinkor neighbourhood in the capital Monrovia.
A local media association, the Liberia Media Center (LMC), published unofficial partial results on Wednesday showing Johnson-Sirleaf just ahead of her main rival Winston Tubman, with just over 96,000 votes to his nearly 80,000 of a total 220,000 votes counted.
Around 1.8 million Liberians registered for Tuesday's election, the second since the fighting and the first to be organized locally. If no candidate wins an outright majority, the two front-runners from a field of 16 will go into a run-off vote scheduled for early November.
Ex-rebel leader Prince Johnson was a distant third with just under 20,000 votes, the LMC said, adding the tally was based on its reporters calling in results that are being pinned up at polling stations across the country.
Official preliminary figures will be released by the National Election Commission on Thursday. Many voters were tuned to radio or television stations as the LMC's unofficial tally came through.
Voting on Tuesday passed off peacefully in Monrovia. Observer groups said they had received no reports of trouble elsewhere in the country of four million people, but have expressed concern that the results could be a flashpoint.
"The mission is of the view that there were no major irregularities and incidents of violence. It estimated that on the whole, the elections of October 11, 2011 were conducted under acceptable conditions of freedom of voters and transparency of the process," Attahiru Jega, head of the observation mission from West African bloc ECOWAS, said on Wednesday.
Johnson-Sirleaf got a pre-poll boost with her award of the Nobel Peace Prize last Friday, but rivals have said Liberians will judge her on her success in fighting poverty in a country with an average annual income of $300 a head.
A dispute over the results of the 2005 election that brought Johnson-Sirleaf to power as Africa's first freely elected female head of state triggered days of rioting.