By Tom Ashby

ABUJA, Dec 16 (Reuters) Nigeria's ruling party was set to pick a reclusive Muslim state governor, Umaru Yar'Adua, as its candidate to succeed President Olusegun Obasanjo in primaries today which some delegates described as a ''coronation''.

The convention ahead of next year's elections has turned into a formality since most other contestants for the People's Democratic Party (PDP) ticket have withdrawn under pressure from Obasanjo.

This positions the publicity-shy governor of Katsina state, a former teacher who suffers from a chronic kidney disease, as favourite to win the landmark poll in Africa's most populous nation and top oil exporter in April.

''There was resistance, but all the governors have stood down. It's now a foregone conclusion that Yar'Adua will be our candidate,'' a senior PDP official said after a breakfast meeting of PDP governors and senators today.

Party sources said presidential hopeful Aliyu Gusau, former National Security Adviser to Obasanjo, was still determined to force a vote at today's convention but stood little chance of success.

Police blocked off roads in central Abuja where the convention was due to be held as the estimated 6,000 delegates converged on the Eagle Square parade ground.

Obasanjo's election in 1999 marked a return to democracy after three decades of almost continuous army rule and next year's poll should mark the first handover from one elected president to another since independence from Britain in 1960.

PUPPET? Yar'Adua's candidacy rests almost exclusively on the support of Obasanjo, who wants to remain a powerful force after he steps down in May, analysts say.

Obasanjo has argued that any successor must deepen his economic reforms, but critics say the former military ruler is trying to protect himself from prosecution when he loses presidential immunity.

''What happens today is intended to make life easy post-transition for Obasanjo. That could be a misjudgement. I don't see Umaru taking orders from anyone,'' said a northern politician who has known Yar'Adua for 30 years.

''Umaru has a mind of his own and is crafty. Because he is quiet, people mistake him for a weakling.'' Yar'Adua appeared as a contender only a few weeks ago and is still largely unknown in Nigeria, having rarely left his home state in the last seven years as governor.

Many in the ruling party fear that Yar'Adua's apparently scant support will embolden the opposition, which is already uniting around a single candidate.

With deep pockets, tight control over security forces and an unrivalled nationwide network, the PDP is the party to beat. But analysts say the opposition is benefiting from disaffection in the PDP, and appears to be uniting around a single candidate.

Two main opposition parties, All Nigeria People's Party (ANPP) and Action Congress (AC), signed an alliance this week that analysts expect to lead to former military ruler Muhammadu Buhari becoming their candidate.

They hold their presidential primaries tomorrow and Monday respectively.

REUTERS MS HT1802