The official result of the presidential election, held on April 21, gave Yar'Adua a crushing victory over his two nearest rivals who immediately challenged the result, alleging vote-rigging and intimidation on a huge scale.

Lawyers had expressed hopes that the presidential tribunal would rule before the end of the year, but Judge James Ogebe on Thursday adjourned until January 28 to give the court time to study hundreds of kilos of documentary evidence.

Speculation has mounted that the tribunal could overturn the result since other election tribunals, at state level, annulled the poll victories of four state governors from the ruling People's Democratic Party (PDP) since October 10. Another PDP governor lost his seat in a Supreme Court decision in June.

The modest, soft-spoken Yar'Adua has made adherence to the rule of law his watchword since he took office on May 29. He has acknowledged that the April polls were flawed and has promised to respect the decision of the presidential tribunal.

His attitude, combined with the shock annulment of five gubernatorial results by courts of law, have fuelled rumours that he might be the next to go.

Official results credited Yar'Adua with 24.6 million votes compared with 6.6 million for Muhammadu Buhari, who was an army dictator in the 1980s, and 2.6 million for Atiku Abubakar, who was vice president at the time of the polls.

BAGS OF EVIDENCE

Lawyers for Buhari and Abubakar have spent the past few weeks presenting enormous plastic bags full of documents they say show evidence of massive electoral fraud.

These included pre-dated results sheets, ballot papers devoid of the security features promised by the Independent National Electoral Commission (INEC) and a report by European Union observers who said the polls were "not credible".

In contrast, lawyers for Yar'Adua and INEC took only one court session, on Thursday, to present all the evidence they intend to use in the defence of the official result. They tendered the presidential result sheet, results from Lagos state and a list of polling wards and stations.

"We have a solid defence. We have closed our case," said Wole Olanipekun, one of Yar'Adua's lawyers, after the hearing.

The court is expected to hear final submissions from the lawyers on January 28 and to set a date for ruling. Lawyers for the challengers said they were confident of victory.

"Our position remains that laws were broken and the election should be nullified," said Emeka Ngige, a counsel to Abubakar.

Should Yar'Adua's victory be overturned, the best scenario would be a peaceful re-run, analysts say. Yar'Adua would probably win again and, if the election were cleaner, he would have a stronger mandate to carry out reforms.

But Nigeria, a chaotic country of 140 million people with a history of botched elections and military coups, could also fall into prolonged limbo with legal battles over how the re-run should be conducted and by whom.