By Nick Tattersall
ABUJA (Reuters) - Nigerians pick their next leader on Saturday in what they hope will be their first credible presidential election for decades, polls which could make or break the country's standing as a democratic leader in Africa.
The election pits President Goodluck Jonathan, the first head of state from the southern, oil-producing Niger Delta, against Muhammadu Buhari, a former military ruler with a reputation as a disciplinarian from the mostly-Muslim north.
Other candidates include former anti-corruption chief Nuhu Ribadu and Kano state governor Ibrahim Shekarau, although they are seen as rank outsiders.
The African giant, home to more people than Russia, has failed to hold a free and fair presidential election since military rule ended in 1999, leaving many of its 150 million citizens with little faith in the benefits of democracy.
But a relatively successful parliamentary election a week ago, deemed credible by observers despite isolated acts of violence, has renewed confidence in the ability of the electoral commission, INEC, to make a break with the past.
Campaigns have also largely been free of inflammatory rhetoric so far, assuaging fears that a race between southern Christian Jonathan and northern Muslim rivals could polarize Nigeria -- home to about equal numbers from both religions.
"If Nigeria gets it right, it will impact positively on the rest of the continent and show the rest of the world that Africa is capable of managing its electoral processes," said former Ghanaian President John Kufuor, who is leading an observer mission from the African Union.
"If Nigeria gets it wrong, it will have a negative influence on the continent with dire consequences," he said.
POWER OF INCUMBENCY
President Jonathan, a former zoology teacher born to a family of canoe makers, is the front-runner. He is backed by the national machinery of the People's Democratic Party (PDP), whose candidate has won every presidential race since 1999.
But he is resented by some in the north, who believe he is usurping the right of a northerner to the presidency for another four years. Jonathan inherited office after his predecessor, northerner Umaru Yar'Adua, died last year in his first term, interrupting a rotation between north and south.
Buhari, a strict Muslim known for his "War Against Indiscipline," is hoping to capitalize on some of the resentment and is likely to win strong northern support despite his Congress for Progressive Change (CPC) being a young party.
"The north wants change for the masses. When you see the people out there who don't have any water or education you can see we need a change," said Hayatudeen Daku, a civil servant from Buhari's home state of Katsina.
"If you go back to when Buhari was leader he looked after the masses. He didn't have time to finish his projects. We hope he will return and finish his work," he said, as people streamed out of Friday prayers from a mosque on a dusty street.
Buhari would need to prevent Jonathan from taking at least a quarter of the votes in two thirds of the 36 states if he is to stop him winning in the first round, a feat which northern support alone is unlikely to guarantee.
Fellow opposition contender Nuhu Ribadu's Action Congress of Nigeria (ACN) party has its stronghold in the southwest, and could help force a run-off. But the two failed to agree a last minute alliance this week, leaving the anti-Jonathan vote split.
The run-up to the polls has been marred by isolated bomb attacks -- including one near an INEC office in the northeastern city of Maiduguri late on Friday in which no-one was injured -- and sectarian clashes in the central "Middle Belt."
The stakes are higher in the presidential race than in the parliamentary polls a week ago, and the security agencies are on high alert. Land borders were closed ahead of Saturday's election and a curfew imposed overnight.
(Additional reporting by Joe Brock in Katsina, Ibrahim Mshelizza in Maiduguri; Writing by Nick Tattersall; Editing by Matthew Tostevin and Peter Graff)