* Central bank governor alleged $20 bln oil fraud
* President suspended governor on unrelated charges
* Several previous audits, graft probes ignored
By Joe Brock and Felix Onuah
ABUJA, March 12 Nigeria's president has authorised a forensic audit of the national energy company, the presidency said on Wednesday, after weeks of public uproar over an alleged $20 billion in missing state revenues.
Central Bank Governor Lamido Sanusi wrote a letter last September to President Goodluck Jonathan saying almost $50 billion in revenues from oil exports from January 2012 to July 2013 had not been remitted to the federation account, in a clear violation of the law.
He lowered the estimate to $20 billion in testimony to a Senate committee investigating the case last month, days before he was suspended by Jonathan for what the president said was unrelated "financial recklessness" and "gross misconduct" at the central bank. Government sources and a wide spectrum of the public believe his removal was politically motivated.
The Nigeria National Petroleum Corporation (NNPC) has repeatedly denied Sanusi's allegations and the presidency, which says they are unfounded, has not responded until now to calls for an independent audit.
Africa's biggest oil producer and the continent's second-largest economy has a reputation for corruption but the scale of the alleged oil graft is unprecedented and Sanusi is the most high-profile figure to raise issues directly to the president.
Sanusi was an internationally respected central bank governor and financial markets were rattled by his suspension with the naira currency briefly dropping to a record low.
Nigeria's Finance Minister Ngozi Okonjo-Iweala and a Senate committee investigating the graft allegations have both called for a forensic audit of NNPC since Sanusi presented evidence.
Jonathan's opponents say the suspension of Sanusi shows he is soft on corruption, a year ahead of what is expected to be the most closely fought presidential election since Nigeria ended military rule in 1998.
"The Presidency wishes to reaffirm that Mallam Sanusi's suspension has absolutely nothing to do with his unproven and inconsistent claim," the presidency said, referring to Sanusi by the title Mallam, given to learned Muslims.
"Mallam Sanusi's allegations are patently untrue. But Government is making no effort to bury them as he falsely claims," the statement said, adding that "reputable international firms" would carry out the audit.
According to Sanusi's testimony, the biggest gap in accounting is for $8.5 billion the NNPC says it retained from revenues during the 19-month period to cover subsidies it was owed on importing gasoline and kerosene.
A directive in 2009 by then President Umaru Yar'Adua, who died in May 2010, had scrapped kerosene subsidies. Petroleum Minister and NNPC chair Diezani Alison-Madueke acknowledged this but told the senate committee they were still paid, contrary to the law, to prevent hardship for millions of poor Nigerians.
NNPC says it buys kerosene at 150 naira ($0.91) a litre and sells it to suppliers at 50 naira per litre. But the retail rate is still above 150 naira, which Sanusi said proves the subsidy is a racket to benefit chosen friends in the kerosene business.
"It is fine to have a forensic audit but I think it is merely a way to keep us satisfied for a little while," Senator Bukola Saraki, who is sitting on the investigating committee, told Reuters this week.
"The minister of petroleum and of finance admitted there is no subsidy on kerosene. Do we need to wait for a forensic audit for the government to stop breaking the law?" Saraki added.
Several probes of NNPC since Jonathan won an election in 2011 have alleged widespread fraud inside what has been described as one of the world's most opaque state oil companies, but little has been done to change the way NNPC operates.
A probe in 2012 by the former head of Nigeria's anti-corruption body, Nuhu Ribadu, recommended an overhaul of NNPC because it lacked transparency in the way it sold oil, wielded too much power and was a vehicle for corruption.
After public outcry, Jonathan ordered three white papers to be written, analysing the report, but they were never produced.