IRA FRAGMENTATION, PEACE-TALK BARRIER SEEN IN BOMBING'S WAKE.

Byline: John Darnton The New York Times

The bomb that caused so much damage in downtown Manchester on Saturday morning - and which bears all the trademarks of the Irish Republican Army - is widely seen as the most devastating setback yet to Northern Ireland's tortured peace effort.

Those who have followed the Republican movement in its 25-year struggle to pry the province from British rule now believe that the IRA is either breaking into factions or is back under the sway of militants ready to forswear negotiations.

``It certainly looks like the IRA is split,'' said Tim Pat Coogan, the Irish writer whose books bring him into contact with the organization. ``I think there's a war party that opposes the talks, and they're certainly not taking any orders from the peace faction.''

The bomb, contained in a truck parked near a busy shopping area, may turn out to be the largest one ever exploded by the IRA in England. Acting on coded telephone warnings, the police were able to clear the immediate area and so avert deaths, but more than 200 people were injured, 16 of them seriously enough to spend the night in the hospital.

Coogan and other analysts say the blast undercut the authority of Gerry Adams, president of Sinn Fein, the political wing of the IRA. Like a similar bomb in London in February that broke a 17-month cease-fire, it indicated that Adams was not succeeding in his campaign to convince the militants that gains could be won politically.

``It is a shattering blow to Adams and those around him,'' said David McKittrick, a journalist and author of ``The Nervous Peace,'' a book about the period of the cease-fire. ``He had seemed to be in the ascendancy, but now the army council'' - the seven-man IRA military leadership - ``is calling the shots.''

``I still think he's won the argument in the broad sense,'' McKittrick said. His approach has massive endorsement among the wider movement. It's hard to say, but it looks as if the army council is going one way and everyone else is going the other way.''

How much political damage the bomb has caused the IRA was seen Sunday in statements by Prime Minister John Bruton of Ireland. He said his Cabinet would meet Tuesday to ``review very seriously and fundamentally our relationship with Sinn Fein and the Republican movement as a whole.''

Bruton called the bomb ``a slap in the face to people who have been trying, against perhaps their better instincts, to give Sinn Fein a chance to show that they could persuade the IRA to reinstate the cease-fire.''

At the same time, the explosion stiffened the resolve of unionists - the Protestants who want Northern Ireland to remain British - that Sinn Fein not be allowed to sit at the negotiating table unless it meets the condition of giving an unequivocal guarantee that it forever renounces all use of violence.