LONDON — PRIME Minister Margaret Thatcher is facing serious security challenges from both sides of the religious divide in Northern Ireland. A massive bomb exploded Sept. 22 at a military barracks in Deal, Kent, killing 10 young Royal Marine bandsmen and exposing grave inadequacies in arrangements for preventing terrorism against ``soft'' targets in England. The bomb was the work of the outlawed Irish Republican Army (IRA).
The Deal barracks had been guarded not by regular police or military personnel, but by a private security firm whose members, it is being alleged, receive minimal antiterrorist training. Mrs. Thatcher has ordered an immediate inquiry into arrangements at military installations around the country.
At the same time the British authorities in Northern Ireland have been embarrassed by a spate of security leaks from police stations in the province. Scores of files, including names and photo montages of suspected IRA terrorists, were stolen and supplied to members of the Ulster Volunteer Regiment (UVR), a mainly Protestant body which helps other British military units preserve security in the province.
The UVR is known to contain some extremists with connections to Protestant paramilitary terrorist groups.
The leaks have sparked a crisis in relations between London and Dublin. The Thatcher government has been forced to order an urgent inquiry into the leaks.
In Dublin, news of the security leaks has caused dismay. The Irish prime minister, Charles Haughey, is concerned that the Anglo-Irish Agreement signed four years ago as a framework for addressing the Ulster problem is being put in jeopardy.
His concern turned to anger when it was confirmed that some of the files stolen from police stations in the province contained material earlier supplied to the authorities in Northern Ireland by the Garda, the police force in the Irish Republic, under the terms of the Anglo-Irish Agreement. Following the disclosure, the Irish Cabinet intends to review its policy on coordination with security forces in Northern Ireland.
The Thatcher government has been placed in an awkward position by the bomb at Deal. On this occasion, the IRA appears to have deliberately chosen a ``soft'' military target, knowing that it would be relatively easy to penetrate the perimeter wire and plant a bomb.
It was alleged at the weekend that there had been earlier plans to tighten up security at the Deal barracks, but that they had been delayed in the Whitehall bureaucratic machine. An IRA bomb at a barracks near London early this year killed one person.
The government's larger problem is that there are literally dozens of soft military targets around Britain. The defense secretary, Tom King, condemned the Deal attack as an example of the IRA's ruthless savagery, but his officials privately concede that there is probably no way of ensuring total security at all potential military targets.
British police believe the bombers were part of an IRA combat squad who have been responsible for a string of outrages in England and West Germany since early 1987. They usually choose targets in or near military installations. Earlier this month the wife of a British soldier in West Germany was murdered by IRA gunmen.