Lagos:  Nigerian President Goodluck Jonathan and his main rivals are expected to formally declare their candidacy for January elections this week and the political temperature is already rising. From alleged death threats against a presidential aspirant's adviser to calls from the opposition for the date to be postponed, the vote looks set to be just as contentious as previous elections in Africa's most populous nation. The start of the campaign is still a month away and doomsayers are already predicting the worst.

"The end of a power-sharing arrangement between the Muslim north and the Christian south, as now seems likely, could lead to post-election sectarian violence, paralysis of the executive branch, and even a coup," former U.S. ambassador to Nigeria John Campbell said in an article in Foreign Affairs magazine. "Nigerians have long danced on the edge of the cliff without falling off. Yet at this juncture it is difficult to see how Nigeria can move back from the brink," he said.

Many Nigerians do not share his pessimism. Jonathan's candidacy may be controversial because of a ruling party pact that power rotates between north and south -- Jonathan is a southerner and the next president should be a northerner if the agreement is upheld. But the power of the incumbent is historically so strong that if he stands, the popular vote will back him, his supporters say. Though they may sound like familiar campaign pledges to some, for his supporters, Jonathan's promises to end chronic power shortages and better manage the economy mean Nigeria is on the brink not of disaster but of a major step forwards.

Nigeria's foreign minister said Campbell had it wrong. "This respected former U.S. envoy appears to take delight in inciting instability in Nigeria with his entire thesis based on a worst-case scenario and seeming relish in willing it to occur," Odein Ajumogobia said. "Nigeria is committed to organising credible elections in 2011 and in spite of the acknowledged and self-evident challenges posed by the proposed timetable, the process is moving forward in a credible and transparent manner."

Opposition parties have voiced concern over an election timetable, announced last week, which gives little room for a badly-needed overhaul of the electoral roll and a period of just two weeks for the registration of more than 60 million voters. The Independent National Electoral Commission (INEC) has a budget of more than $500 million, which it has said it will largely spend on 120,000 electronic voter registration machines.

"In a semi-literate computer society, when and how will the INEC ad hoc officials be trained to efficiently man the machines in 120,000 centres nationwide in so short a time," asked the opposition Conference of Nigerian Political Parties (CNPP).

Along with opposition party the Action Congress of Nigeria (ACN), the CNPP urged Jonathan to push back the election date.

CANDIDATES SET TO DECLARE

Jonathan and his office have been officially coy on whether or not he will stand, but last week's reshuffle of the military top brass and policy announcements akin to campaign promises -- from privatising the power sector to setting up a sovereign wealth fund -- leave few Nigerians in much doubt over his plans.

One of Nigeria's state governors let slip last week the incumbent had already told ruling party members he intended to run, and Jonathan -- in his trademark fedora and traditional caftan-like attire -- is expected to declare his candidacy in Abuja on Saturday, according to local newspapers.

One of Jonathan's main challengers for the ruling party nomination, former military ruler Ibrahim Babangida, known by his initials IBB, has been less secretive about his ambitions. He has already declared his candidacy several times and launched a campaign website, but plans a formal "flag-off" ceremony in a main square in Abuja on Wednesday. "IBB will use the opportunity to interface with Nigerians and explain to them why he needs to return to office to salvage the country," campaign spokesman Kassim Afegbua said.

The ruling People's Democratic Party (PDP) candidate has won every presidential election since the end of military rule 11 years ago and the primaries, which must be completed by the end of October, are set to be the most fiercely contested yet.

IBB and former vice president Atiku Abubakar, also seeking the PDP nomination, are both northerners. Kwara state governor Bukola Saraki from the centre-north is expected to declare this week and national security adviser Aliyu Gusau is also said to want the party's ticket. Alleged death threats against IBB's campaign manager, media mogul Raymond Dokpesi, already suggest a fierce battle.

"Nigerians know those who are the masters in the art of political violence and it is not President Goodluck Ebele Jonathan," presidency spokesman Ima Niboro said in response to suggestions Jonathan's camp was behind the alleged threats.

Ostensibly religious violence in Nigeria's Middle Belt -- the region between the mostly Muslim north and predominantly Christian south -- has so far been contained in specific areas and triggered by local, rather than federal, politics.

But former U.S. envoy Campbell is not alone in fearing that should the race to win the PDP nomination become focused around power-sharing between north and south, that could change. "The internal affairs of the PDP are threatening to become a a catalyst for violence that could engulf the whole nation, and make a mess of President Jonathan's consistent pledge to organise a free, fair and credible election," the opposition ACN said.

*  For more Reuters Africa coverage and to have your say on the top issues, visit: af.reuters.com/ )

*  By Nick Tattersall with additional reporting by Felix Onuah in Abuja; writing by Nick Tattersall; editing by Philippa Fletcher)

*  © Thomson Reuters 2010. All rights reserved.