PRIME Minister Margaret Thatcher has said for the first time that Irish terrorists are waging a guerrilla war in mainland Britain and that a new set of measures must be devised to combat an intensifying campaign of violence. She has decided to convene - and is expected to chair - an emergency meeting this week of government ministers and security advisers. Downing Street sources indicated that the meeting would focus on ways of heading off the escalating campaign of violent attacks by the outlawed Irish Republican Army (IRA) on so-called ``soft'' targets in Britain.
Mrs. Thatcher's hand was forced by an IRA gunfire attack on Sir Peter Terry, a former governor of Gibraltar, at his home in Staffordshire last week. Sir Peter, who was the queen's representative in the British colony when British security forces there shot dead three IRA members in 1988, was wounded, but survived the attack. His wife Betty was also injured.
The couple had no special security protection, and the gunmen fired through the window of their home.
A day earlier, IRA gunmen shot and seriously wounded an Army sergeant outside a recruiting office in the London suburb of Finchley, which is Thatcher's parliamentary constituency. The attackers later escaped on a motorcycle.
Yesterday, masked gunmen shot to death a part-time member of Northern Ireland's security forces, Britain's Press Association news agency said.
The shooting of Sir Peter and his wife was the 19th incident involving the IRA on the British mainland in the last 12 months. Security officials say it shows the virtual impossibility of giving security protection to all people whose work at some time has turned them into potential IRA targets.
Thatcher government targeted
IRA attacks have been made this year on targets selected to remind the British public that the terrorists bitterly oppose the Thatcher government. For example, bombs were exploded at the Carlton Club in the heart of London, a favorite venue of Conservative politicians, the London Stock Exchange, and the home of a former Conservative Party treasurer.
Thatcher, who was on a visit to Eastern Europe, said last week: ``The number of things that are happening now make it important that we look once again to see if there is anything further we can do to step up our security and defense against this guerrilla warfare.''
Her use of the latter phrase took her own officials by surprise. Her government had previously viewed the IRA as a group of common criminals whose activities had to be countered within normal civil law.
She appeared to move from this position, saying: ``We must look to see if there are ways of stepping up our security and defending against guerrilla warfare.''
A spokesman for the prime minister later said: ``Security is always under review, and she will be looking at it in the light of recent events.''
Government sources say the emergency meeting would launch a wide-ranging overhaul of security safeguards. Thatcher wants closer cooperation from the Irish Republic in tracing IRA suspects, weapons, and bombmaking equipment.
Security experts mostly agree that the Dublin government could do more to help, but believe also that it would be impossible to afford protection to the thousands of people and buildings regarded by the IRA as ``soft targets.''
``In Northern Ireland, there are 32,000 police officers and soldiers to protect 1.5 million people. To provide the same level of protection on the British mainland would require 1.2 million police and massive investment in security measures for people at risk,'' says Chris Ryder, a specialist writer on Irish security affairs. `New phase' of IRA violence
Mr. Ryder interprets the year-long surge of violence as ``a new phase in what the IRA sees as the long war necessary to free Ireland from what it regards as British occupation.''
Other terrorism experts see the attack on Sir Peter as an example of the failure of potential IRA targets to take simple measures to protect themselves. ``A basic understanding of personal security is more important than armed guards or fancy electronic surveillance equipment. It doesn't help when people give the terrorists information on a plate, as Sir Peter did with his address in the telephone book and Who's Who,'' says Ian Geldard, editor of the newsletter Terror Update.
Mr. Geldard says IRA units operating on the mainland are better trained and more professional than the gangs operating in the 1970s, when the main targets were hotels, bars, and restaurants.
Antiterrorist police believe the IRA has two operational cells on the mainland - one in London, the other 200 miles away in the Midlands. They are thought to be separate units working in close contact with local helpers who provide safe houses, vehicles, and other forms of assistance.
Geldard says he believes the IRA's high command allows the cells to choose their own targets. This minimizes the risk of security leaks.
This higher degree of organization is believed to have persuaded Thatcher that IRA members can now be better described as guerrillas than as criminals.
The murder in July of Ian Gow, one of Thatcher's closest political advisers, officials say, deeply shocked the prime minister. Gow, who was blown up by a bomb placed under his car at his Sussex home, was another ``establishment'' figure. He was deeply opposed to the IRA and to any move that threatened to loosen Northern Ireland's ties with the Britain.
After the attack on Sir Peter, the IRA claimed he had been directly responsible for the shooting of the three IRA members in Gibraltar.