(Corrects typo in name 'Siollun', paragraph 19)
* President Jonathan faces Buhari in Feb. 2015 polls
* Buhari seen as tough on corruption, insecurity
* Regional, ethnic factors likely to define contest
By Tim Cocks
LAGOS, Dec 17 (Reuters) - "I am not a rich person, I can't give you a pocketful of dollars or naira to purchase your support," Nigeria's former military leader Muhammadu Buhari wrote to opposition delegates last week before they chose him to contest next year's presidential election.
"I want a Nigeria ... where corruption no longer trespasses into our institutions and national behaviour."
His words struck a chord with Nigerians fed up with leaders filling their pockets. They also highlight his main selling point: during his previous stint in power from 1983-85 he is widely believed to have kept his fingers out of the till.
Buhari faces President Goodluck Jonathan in a Feb. 14 election in Africa's biggest economy that analysts think may be too close to call.
Graft scandals, most recently a claim by a former central bank governor that between $10 billion and $20 billion owed to state coffers by the national oil company were not remitted, have fuelled public anger. The government has promised an audit.
Buhari has growing appeal among an intellectual class in whose minds he has taken on almost messianic qualities as the man who can save Nigeria. Others remember less celebrated bits of his past -- like crackdowns on press freedom and detaining political opponents without charge.
Either way, he will also prove a divisive figure in a vote in which ethnic and religious sentiments remain paramount.
"People love him or they hate him. There's no middle ground," said Kayode Akindele, CEO of consultancy 46 Parallels.
His image as a sandal-wearing ascetic has appeal in a nation where power and champagne-swigging wealth often go hand in hand.
"He doesn't love money. He doesn't care about making money. This is what Nigeria needs of a leader," said Haruna Mohammed Yogara, an opposition All Progressives Congress (APC) official who voted for Buhari to represent the party in the primaries.
At the same time, the government's failure to quell an Islamist insurgency in the northeast has heightened the general's appeal as a military strongman, a type Nigerians were pretty sick of when democracy returned in 1999 after decades of army rule.
Buhari's message is simple: Nigeria's two biggest ills are corruption and insecurity, and he cracked down on both in 1983.
"He's been tested on both issues before and he passed," APC Senator Babafemi Ojudu told Reuters.
Then, as now, Nigeria faced economic turmoil from collapsing oil prices. Then president Shehu Shagari was accused of wasting money on corruption -- much as this government has been dogged with oil corruption scandals.
Insecurity, from militia in neighbouring Chad, threatened Nigeria's remote northeast, just as Boko Haram does today. Buhari, as army commander under Shagari, drove the Chadian fighters out of Nigeria, even invading Chad to secure a buffer.
"He beat them black and blue and chased them into Chad Republic. He can do it again (with Boko Haram)," Ojudu said.
After deposing Shagari he began a "war against indiscipline" to weed out corruption, armed robbery and drug trafficking.
"Immediately after its coup (the new government) closed all borders and arrested ... 475 politicians and businessmen for corruption," writes Max Siollun in his 2013 book Soldiers of Fortune. "Rooms stacked with illicit cash" were discovered in politicians' houses.
Even those willing to overlook his autocratic past might question whether he can keep his promises. Corruption is so entrenched that dismantling it could take generations.
"People love the anti-corruption, but if they dig a bit deeper: what does it actually mean? And can he pull it off?" said Akindele, adding that it could mean turning on some of his top backers in the APC, which he is unlikely to be able to do.
Power in democratic Nigeria depends on patronage networks, and feeding them is essential if a politician wants to keep it.
Promises to restore security after a brutal five-year insurgency by Boko Haram also might be easier to make than keep, with the Islamist group demonstrating remarkable resilience.
But sources in both parties say more prosaic factors may influence voting. Buhari, a Muslim northerner, will do better in the north, where he's hugely popular. Jonathan will sweep much of the overwhelmingly Christian south and southeast -- his home oil producing Niger Delta region and areas around.
Christians in the religiously-mixed "Middle Belt" will vote Jonathan; their Muslim neighbours, Buhari.
Much will depend on whether the 50-50 split Christian-Muslim Yoruba southwest, including Nigeria' biggest city Lagos, votes for Jonathan. It did last time, but since then southwestern elites have turned against him. Buhari's party power base is now in Lagos -- last year it was seen as largely a northern party.
"Last year people were frustrated the alliance fell apart so voted for Jonathan out of protest," Ojudu said.
"That won't happen again." (Writing by Tim Cocks; Editing by Giles Elgood)