(Adds McGuinness remarks on police "cabal", further detail, context)
By Maurice O'Neill
BELFAST, May 2 (Reuters) - Police in Northern Ireland are seeking to extend the detention of Sinn Fein leader Gerry Adams for questioning into a 1972 murder, party colleague and Northern Ireland first deputy minister Martin McGuinness said on Friday.
Adams's arrest on Wednesday over the abduction and killing of Jean McConville was among the most significant in the British province since a 1998 peace deal ended decades of tit-for-tat killings between Irish nationalists and pro-British loyalists.
The Police Service of Northern Ireland (PSNI) had until 8 p.m. (1900 GMT) on Friday to charge Adams, a former Irish Republican Army spokesman, release him or secure permission of a judge to extend his detention.
"We have been told within the last couple of hours that the PSNI are seeking an extension to Gerry Adams' detention. We were told that will take place at 3 o'clock today," McGuinness told journalists in Belfast. "I believe Gerry Adams will be totally and absolutely exonerated."
Reviled by many in Britain as the face of militant Irish nationalism in the 1980s during the IRA campaign against British rule of Northern Ireland, Adams reinvented himself as a Northern Ireland peacemaker and then a leading opposition parliamentarian in the Irish Republic.
But Adams, 65, has been dogged throughout his career by accusations from former IRA fighters that he was involved in its campaign of killings, a charge he has repeatedly denied.
He offered to speak to police about McConville's killing in late March after tapes that apparently accuse him of participation were released by researchers in the United States.
Adams has always denied membership of the IRA and on Wednesday said he was "innocent of any part" in the killing, which he said was "wrong and a grievous injustice to her and her family".
McGuinness repeated accusations that the decision by police to arrest Adams was politically motivated. "There is a cabal in the PSNI that have an agenda, a negative and destructive agenda to both the peace process and to Sinn Fein.
"We, under the leadership of Gerry Adams, have not intention of allowing these elements," said McGuinness.
The former IRA commander also said that it may be difficult to contain anger among Irish nationalists about the arrest.
"We believe that the anger and resentment out there among the community is something we as Irish republicans have to manage. We are trying to handle this situation in a very calm way," McGuinness said. (Writing by Conor Humphries; Editing by Mark Heinrich)