* U.S. ready to help Nigeria fight corruption
* Electoral reform seen as vital
* Oil delta, regional security on agenda
ABUJA, Aug 12 (Reuters) - U.S. Secretary of State Hillary Clinton will take a tough line with Nigeria on Wednesday over rampant corruption and urge Africa's biggest energy producer to implement badly-needed electoral reforms.
A month ago President Barack Obama visited nearby Ghana on his first official Africa trip, an itinerary seen by some Nigerians as a damning indictment of their nation's record on governance and graft.
"Nigeria is undoubtedly the most important country in sub-Saharan Africa," Assistant Secretary of State for African Affairs Johnnie Carson told reporters en route to Abuja.
"It also faces challenges with respect to corruption and has been described by a number of organisations as the most corrupt state in Africa and we all know what corruption can do to public confidence," he said.
Mismanagement and graft over decades have imperilled Nigeria's development, deterred investment, undermined democracy and deepened conflicts such as the insurgency in the southern Niger Delta and bouts of religious violence in the north.
President Umaru Yar'Adua took office more than two years ago in Africa's most populous nation pledging respect for the rule of law but diplomats and analysts say the fight against corruption has faltered under his leadership.
Nuhu Ribadu, a former anti-corruption chief seen as a key reformer by the United States and other foreign powers, was removed from his post months after Yar'Adua came to power in May 2007 and has since fled the country, fearing for his life.
"The anti-corruption commission in Nigeria has performed weakly since the departure of Mr Ribadu," a senior U.S. official travelling with Clinton said.
"We will seek to be helpful in trying to work with him on strengthening their anti-corruption efforts if there is a desire on the part of the Nigerians to do so."
Diplomats in Nigeria, who share concerns about the country's governance, said they would be watching to see how much of a tough message Clinton was prepared to convey in public.
"Clinton will to some extent be setting the tone of how the wider international community decides to view Nigeria," one diplomat in the capital Abuja said, asking not to be named.
In the decade since the end of military rule, elections have been far from exemplary in a country that considers itself the biggest democracy in the black world. Corruption remains endemic, poverty widespread and infrastructure shambolic.
The April 2007 polls that brought Yar'Adua to power were so marred by ballot-stuffing and voter intimidation that local and foreign observers said they were not credible.
"Nigeria is at something of a political crossroads. Its last elections approximately two years ago were deeply flawed," the U.S. official said, speaking on condition he not be named.
Legislation is before parliament to reform the electoral system in an effort to prevent a repeat performance at nationwide polls in 2011, but diplomats say the teeth have been taken out of the reform bill and it is now too late to make the constitutional changes necessary. [ID:nLP935412]
Clinton is also likely to seek an update on the status of a 60-day amnesty period in the Niger Delta, an effort to end years of militant attacks on the oil industry which have prevented Nigeria from pumping much above two thirds of its capacity.
Central Bank Governor Lamido Sanusi said on Tuesday the crisis was costing Nigeria $1 billion a month in lost revenues.
Yar'Adua holds the rotating chairmanship of the Economic Community of West African States (ECOWAS) and regional security is also expected to be on the agenda.
A string of elections in West Africa this year has passed off peacefully, but most have been backward steps for democracy with the potential to incite further power grabs. [ID:nLB693654]
Last week Niger's President Mamadou Tandja declared victory in a referendum he called to extend his term of office in the uranium-producing Saharan state, defying international criticism and domestic protests that the move was anti-constitutional.
"We believe that it is important that the constitution in this country be followed. This is a position held not only in the United States but in ECOWAS," the U.S. official said.
For a factbox on the key issues facing Nigeria, click [ID:nL211051]. (For more Reuters Africa coverage and to have your say on the top issues, visit:
) (Writing by Nick Tattersall; Editing by Michael Roddy)
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