* Former head of IRA political wing denies involvement in killing
* Murder of mother of 10 among most controversial of 'Troubles'
* Adams head of Ireland's second largest opposition party
* Says concerned about questioning during EU elections (Changes date, adds background)
By Maurice Neill and Conor Humphries
BELFAST/DUBLIN, May 1 (Reuters) - Northern Ireland police arrested Sinn Fein leader Gerry Adams on Wednesday as part of an investigation into one of the province's most controversial murders, a move that sent political shockwaves through Belfast and Dublin.
The man reviled in Britain as the spokesman for the Irish Republican Army in the 1980s, Adams reinvented himself as a Northern Ireland peacemaker and then as a populist opposition politician in the Irish parliament.
His Sinn Fein party said he was arrested by police investigating the 1972 abduction and murder of mother of 10 Jean McConville on Wednesday evening and could be held for up to 48 hours without being charged.
Adams, who has always denied membership of the IRA said he was "innocent of any part" in the killing, which he said was "wrong and a grievous injustice to her and her family."
"Well publicised, malicious allegations have been made against me. I reject these," he said in a statement.
Sinn Fein deputy leader Mary-Lou McDonald said the decision to make the arrest weeks before elections across Ireland, was influenced by demands from political rivals and "elements of the old guard" within the Northern Ireland police service.
"The timing as far as we are concerned is politically contrived," she said.
BODY ON BEACH
McConville's body was found in 2003 on a beach in county Louth, which Adams now represents in Ireland's parliament. The IRA suspected McConville of being an informer, a charge her family has always denied.
She was suspected of having gone to the aid of a British soldier serving in the province, which was torn by violence between Catholic republicans and pro-British Protestants for three decades.
The investigation into McConville's killing has been revived by the release of a series of taped interviews given by former fighters from the Northern Ireland conflict for a research project at Boston College in the United States.
The Northern Ireland police took legal steps to acquire the interviews, parts of which have already been released after one IRA interviewee died.
1980s MEDIA BAN
As head of the political wing of the Irish Republican Army, Sinn Fein, Adams was a pariah in 1980s Britain, banned from speaking on British airwaves, forcing television stations to dub his voice with that of an actor.
Former Prime Minister John Major once said the thought of sitting down with him "turned his stomach". Adams emerged from the political cold in October 1997 when he shook hands with Labour Prime Minister Tony Blair at their first meeting.
A year later Adams helped broker a peace deal that largely ended three decades of violence between Catholic militants seeking union with Ireland and mainly Protestant militants, who wanted to maintain Northern Ireland's position as a part of Britain.
Since that peace deal Adam's role as a statesman has grown. He is a regular visitor to the White House and was a guest of honour at the funeral of Former South African president and anti-apartheid hero Nelson Mandela last year.
But the murder of McConville, has haunted him and has been repeatedly raised in interviews during his career as a member of the Irish parliament.
Northern Ireland's fragile peace has been shaken by investigations into historic crimes in recent years, with probes into pro-British militants widely seen as one of the sparks for some of the 2013 street violence that was the worst for years in the province.
It is unclear what affect the arrest might have on Northern Ireland's power-sharing government, whose deputy first minister, former IRA commander Martin McGuinness, is also a member of Sinn Fein. He has reinvented himself as a statesman, meeting the British Queen in 2012.
The arrest will have major ramifications in the Republic of Ireland where Adams leads the second largest opposition party Sinn Fein, campaigning on opposition to the government's austerity policies.
An image makeover to make him more palatable to a public where suspicion of Sinn Fein's role in the Northern Ireland troubles runs deep has included a twitter feed that recounts the escapades of Adam's teddy bears and Pilates classes.
He was forced to disassociate himself from his brother Liam who was sentenced last year to 16 years in prison for raping his daughter when she was a child. The Public Prosecution Service decided not to prosecute Gerry over allegations of withholding information from the police on the issue.
Adams, who is campaigning for Sinn Fein candidates in European elections and local elections on May 23, also suggested his arrest could be politically motivated.
"I do have concerns in the middle of an election about the timing," he told Irish television station RTE before he arrived for questioning. (Editing by G Crosse, Guy Faulconbridge and Andrew Hay)