* Mines, corruption and food prices focus of Bio's criticism
* Election to test Sierra Leone stability, progress
By Simon Akam
FREETOWN, Oct 9 (Reuters) - Sierra Leone's main opposition candidate in a November election has kicked off his bid for the presidency with an attack on the incumbent's record on minerals deals, corruption and rising food prices.
The comments from Maada Bio, a former junta leader seen as Ernest Bai Koroma's biggest threat for re-election in the Nov. 17 vote, on Tuesday divided the local press and were rejected by the president's camp as political manoeuvring.
Koroma is seen as favourite but Bio has strong support, especially amongst youth and will likely force a run-off vote.
The election will be a crucial bellwether of the country's progress a decade since its civil war ended.
"Under Obai, our mineral wealth has been more mortgaged and with lesser returns to the citizenry than before he took office," Bio said, referring to Koroma by a form of his middle name, in a speech broadcast on a local radio station on Monday night.
Sierra Leone is rich in natural resources, including iron ore, bauxite, diamonds and rutile but was at war for most of the 1990s and is struggling to rebuild. It has found oil though it is unclear yet whether there are commercially viable quantities.
In an interview with Reuters last year Bio said if elected he would review minerals deals, some of which have been criticised for failing to conform to Sierra Leone's own laws.
He did not provide any further details during interviews with several radio stations but did attack Koroma's record on graft.
"The abuse of public office for private gain is growing into an art and impunity has reached intolerable levels, higher than before he took office," Bio said.
When he came to power in 2007 Koroma promised there would be "no sacred cows" in his administration. However, last week he retained his vice president as running mate despite Samuel Sam Sumana's involvement in a series of scandals.
SECURITY A CONCERN
Politics in the country of six million is largely drawn along ethnic lines.
The ruling All People's Congress draws its support from the Temne and Limba peoples of the north. Bio's Sierra Leone People's Party has its base in the Mende of the south and east.
"On Nomination Day... Bio Fires Warning Shot," The New Storm splashed on its front page. "Maada Bio's days are numbered," The Torchlight newspaper, which described the challenger's nomination as lacklustre, hit back.
A United Nations peacekeeping force left the country in 2005. While the country has remained largely peaceful since the war, it has seen pockets of rioting over the last year.
Last week, Richard Howitt, the head of the European Union's election observer mission, said security around the election was the team's biggest concern.
Bio blamed Koroma for a spike in food prices, saying they have risen three-fold since he took office. Prices have risen in the West Africa state, though Nasri Halloway, a rice importer, said it was closer to doubling than tripling.
Unisa Sesay, Koroma's spokesman, dismissed Bio's criticism. "All the points he's making are only in the nature of politicking," he said.
Sesay said Sierra Leone's anti-graft commission was free of political interference. He accepted that some mistakes had been made during negotiations but said all mining contracts had been ratified by parliament.
"We are all human beings ... We are not perfect, we don't have all the information," he said, adding that a process of reviewing deals was already under way.
(Writing by David Lewis and Richard Valdmanis)
Keywords: SIERRALEONE ELECTION/