LONDON — A SERIES of major security lapses in Northern Ireland is fueling a crisis in relations between London and Dublin. The government of the Irish republic is questioning whether the Anglo-Irish Agreement, struck four years ago to chart a future political course for Ulster, can survive. British authorities are struggling to salvage the credibility of the agreement.
The crisis arose on Aug. 29 when large numbers of photographs and police documents referring to suspected terrorists of the outlawed Irish Republican Army (IRA) began arriving at television and newspaper offices in Northern Ireland and England. The Royal Ulster Constabulary (RUC) admitted that the documents were genuine.
Inquiries confirmed that some of the photos and documents had been stolen from Ulster police stations and handed to Protestant paramilitary groups. Others had apparently been passed to Protestant gunmen by members of the Ulster Defence Regiment (UDR), a heavily Protestant military force which helps to preserve security in Northern Ireland.
The leaks, which involved details of hundreds of suspected IRA terrorists, became the focus of a special British inquiry. They also prompted the Dublin government, which in general supports the Roman Catholics of Northern Ireland, to accuse Britain of permitting collusion between the Ulster security authorities and Protestant terrorist groups.
The first Irish broadside was fired on Sept. 15 when British and Irish ministers met in Dublin. Seven hours of discussions ended with Ireland's foreign minister, Gerry Collins, demanding a thorough investigation and major reforms in the UDR. Britain said it would look into the question.
Three weeks later, by which time there had been a total of 13 cases of leaked documents, the two sides met again. Prime Minister Margaret Thatcher meanwhile had publicly praised the UDR for its contribution to security in Northern Ireland and had agreed that its members be issued plastic bullets for dealing with civil disturbances.
The Anglo-Irish meeting was predictably frosty. Mr. Collins again demanded an overhaul of the 6,500-strong UDR. Britain's Northern Ireland secretary, Peter Brooke, refused. But on Sunday, 300 Ulster police in a dawn raid arrested 28 UDR members. It was later confirmed that security photographs were among materials seized by the police.
The raid by the Royal Ulster Constabulary marked the first time that one element in Northern Ireland's security forces had been used to police another.
The UDR, formed in 1970, is a locally recruited regiment of the British Army. Ninety-six percent of its members are Protestant. The RUC, a civil police force, is also heavily Protestant.
Ulster Catholics, with some encouragement from the government in Dublin, often express anxiety about the objectivity of the UDR and the RUC. Five years ago John Stalker, then deputy chief constable of Manchester, England, was ordered to investigate six deaths of unarmed Catholics, five of them known terrorists, shot by police.
Mr. Stalker met obstruction from the RUC. Later, amid accusations about his private life that were later proved false, he was removed from the inquiry and resigned from the police.
Most worrying for the Thatcher government are suggestions that the leaks of security documents were part of an attempt by Ulster Protestants to destabilize the Anglo-Irish Agreement.
The Rev. Ian Paisley and other Ulster Protestant leaders see the agreement as an effort by London and Dublin to outflank them by imposing unity on the two parts of Ireland. Britain and Ireland have consistently denied this.
Mrs. Thatcher has portrayed the agreement as a framework for political consultation and cross-border measures to combat terrorism, whether it be by Catholic or Protestant. Mr. Paisley and his followers, however, have sworn to destroy the agreement.
According to officials close to Ireland's Foreign Ministry, the security leaks are part of a campaign to discredit the security authorities in Northern Ireland.
The Dublin government feels that it cannot ignore the leaks, but by demanding reforms that Thatcher is not keen to authorize, they are placing enormous strains on the agreement.
Extremists on both sides of the sectarian divide in Northern Ireland believe they will gain if the Anglo-Irish Agreement has to be scrapped.
The IRA would benefit because cross-border security forces would lose much of their effectiveness. Radical Protestant political groups would see the collapse of the agreement as a major breakthrough in their attempts to prevent religious cooperation in Northern Ireland.
A measure of the dangers involved has been suggested by the reactions of moderate politicians. Seamus Mallon, deputy leader of Ulster's mainly Catholic Social and Liberal Democratic Party, and a British Member of Parliament, has accused the Thatcher government of endangering the Anglo-Irish Agreement by failing to act decisively to end the leaks.
Mr. Mallon tries to avoid hard-line attitudes, but he says he has no alternative so long as what he calls ``obvious collusion'' between the UDR and Protestant militias is allowed to continue.