* Adams arrest and release infuriates both communities
* Local people fear repercussions on streets
* Divisive summer "marching season" is likely flashpoint
By Conor Humphries
BELFAST, May 5 (Reuters) - The arrest of Irish nationalist leader Gerry Adams by police investigating a 1972 murder and his subsequent release have aggravated both the Catholic and Protestant communities in Northern Ireland, just as the divisive "marching season" begins.
So far the volleys of angry rhetoric between committed supporters of Adams's Sinn Fein party and its pro-British rivals haven't translated into violence across Belfast's patchwork of housing estates, which remain divided on sectarian lines.
But the many members of both communities who simply long for the normality enjoyed in the rest of Britain and Ireland fear the consequences of the Sinn Fein leader's four-day police interrogation and release on Sunday.
"There's going to be repercussions on the streets and from both sides. That's just the way things are here," said Dawn Johnson, a 26-year-old Protestant walking in central Belfast on Monday. "One side will play up and then the other, that's always the way here."
This sense of foreboding is shared a short distance away on the Catholic Falls Road. "No one knows what happens next, and don't believe anyone who tells you they do," said Ruari, a 70-year-old retiree. "This matter isn't closed by any means."
The politically committed are angry for differing reasons - nationalists because Adams was held and questioned for so long during an election campaign, and pro-British unionists because he was released without being immediately charged.
After Adams spent his second night in custody at a fortified police station outside of Belfast, his Sinn Fein colleague, Deputy First Minister Martin McGuinness, warned it might be difficult to control nationalist anger over the arrest.
But when Adams was released two days later, with police referring the case to prosecutors for a decision on whether to bring charges, it was unionist protesters who blocked the road and later threw petrol bombs to express their anger at what they said was lenient treatment.
Three decades of violence when the Irish Republican Army (IRA) fought British security forces mostly ended with a peace deal in 1998. But the sectarian conflict between Catholic nationalists seeking Irish union and Protestants wishing to stay in the United Kingdom has yet to be extinguished altogether.
In the pro-British Loyalist bars of the Protestant Shankill Road, all the talk on Sunday night was of how Adams walked free, said Graham, a former inmate of the Maze prison where convicted fighters from both sides were once held.
"People are angry at the police. If we were to get lifted (arrested), we wouldn't walk out after four days," he said, pulling up his trousers to show a Maze tattoo on his leg. "This will kick the trouble off again and it will start very shortly," said Graham, 40, who was released under the 1998 deal.
While the deal has undoubtedly transformed Northern Ireland, sporadic violence has been creeping back in recent years, fuelled by perceptions in both communities that they have received the worse deal from the peace process.
Trouble often flares in the summer months when Protestant groups hold traditional parades to mark military victories dating back to the 17th century. Catholics say these are provocative, and this year's marching season is now getting underway.
Adams, who is a member of parliament in the Irish republic, has been dogged throughout his political career by accusations from former IRA fighters that he was involved in its campaign of killings, a charge he has repeatedly denied.
He says he is "innocent of any part" in the murder of Jean McConville, who was abducted in front of her children from a nationalist area at the height of the IRA campaign in 1972.
After his release, Adams tried to calm fears that his detention could destabilise the British province by pledging his support to the peace process and policing.
But comments by McGuinness during the detention, in which he accused "dark forces" in the police of using "political policing" to target nationalists, may have a lasting effect.
"Sinn Fein overplayed their hand. How can they work with the police after talking in public about 'dark forces'?" said Michael, a 49-year-old unionist, walking on an estate between the Catholic Falls and mainly Protestant Shankill roads.
This would help nationalist militants still opposed to the peace process who have been responsible for the worst violence since 1998. "It plays right into the hands of the dissidents," said Michael, who refused to give his last name.
The Democratic Unionist Party accused Sinn Fein, with which it is forced to share power in the Northern Ireland government, of a "thuggish attempt" at blackmail by suggesting a possible withdrawal of support for the police.
Within hours of Adams's release, police had to deal with disorder in the predominantly Protestant Sandy Row area of Belfast where a number of petrol bombs and stones were thrown.
"What's happened is unsatisfactory for both communities," said Peter Shirlow, a professor of conflict resolution at Queen's University Belfast. "This is seismic event and it is something that will completely keep the heat in the fire of contention in this society."
Last year was one of the most violent since 1998 as Loyalist Protestant youths held daily protests over a decision to stop flying the British flag daily over Belfast city hall.
The riots were widely seen to have been fuelled by moves to prosecute pro-British paramilitary fighters under the same drive to solve past crimes that led to Adams's arrest.
In a sign of the tension, about 100 pro-British activists blocked the road outside the Antrim police station where Adams was held. This forced police to send armoured vehicles and officers in riot gear out of the front gate on Sunday to divert attention as the Sinn Fein leader slipped out the back.
The crowd shouted abuse at the police for defending "murderers".
But on the Falls Road in Belfast, a city where the two communities live cheek-by-jowl, a mural was painted over the weekend with a picture of Adams beside the words "Peacemaker, Leader, Visionary". (Additional reporting and writing by Padraic Halpin in Dublin; editing by David Stamp)