From Our Correspondent in Belfast

WARNING of an imminent attack was issued yesterday to all police and

Army units in Northern Ireland while the four Ulster Defence Regiment

soldiers who were killed by the IRA's 1000lb culvert bomb were out on

patrol. The bomb caused the biggest loss of life suffered by the UDR

since 1983.

Security chiefs issued a warning that an attack was imminent after

suspect overalls had been found half a mile from where the huge

explosion lifted the soldiers' Land-Rover 30ft into the air and hurled

it 30 yards into a field, near Downpatrick, County Down. The warning

followed weekend intelligence reports that the IRA had smuggled a fresh

stock of explosives into Northern Ireland and was intent on a renewed

bombing campaign.

The Irish Prime Minister, Mr Charles Haughey, is to go ahead with a

visit to Belfast tomorrow amid mounting anger at yesterday's killings. A

total of 187 members of the UDR have now been killed through terrorism,

but the reaction to yesterday's attack has been laced with bitter

criticism of the Irish Republic's refusal to extradite suspects.

A lance-corporal and three privates of the UDR were killed instantly

when the explosion wrecked their Land-Rover as it crossed the culvert.

Other soldiers in a vehicle in front of the Land-Rover suffered severe

shock and were airlifted to hospital. The two-vehicle patrol had been

heading towards Downpatrick from Ballykinlar Army barracks when the bomb

exploded, shortly before 8am.

Army headquarters in Northern Ireland last night named the four UDR

men who died. One of the men originally came from Scotland. He was

Lance-Corporal John Bradley, 25, of Cregagh, Belfast, married with a

two-year-old son and a three-month-old daughter. He had recently been

promoted having served four years with the UDR. He formerly served with

the Royal Highland Fusiliers and came from Port Glasgow, Renfrewshire.

The others were: Private John Birch, 28, married with a four-year-old

son. He joined the regiment in February last year and came from

Ballywalter, County Down; Private Steven Smart, 23, single, from

Newtownards, County Down. He had served for 18 months with the regiment

and had previously served in the Royal Artillery; Private Michael Adams,

23, single, also from Newtownards, who had served with the UDR for seven

months, having formerly served with the Royal Engineers.

In a statement the IRA said the attack was carried out by members of

its South Down Brigade.

Coming after recent decisions by the Irish Supreme Court to refuse to

extradite terrorist suspects to Ulster, the attack has heightened

political tensions in the province, especially before Mr Haughey's

controversial visit.

Mr Haughey said yesterday: ''I don't think anybody could seriously

believe that the people who conduct this violence and carry out these

atrocities could have any regard for the decisions of any court. They

follow their own futile agenda.''

He also dismissed suggestions that the refusal of the Supreme Court in

Dublin to extradite former MP Mr Owen Carron had any connection with

today's bombings. ''I couldn't accept any such relationship.

Unfortunately the violence in the north of Ireland is both random and

unpredictable,'' he said.

Angry protests are expected in Belfast tomorrow morning over Mr

Haughey's visit, and a large-scale security operation is likely to be

required when the Irish leader addresses a conference of the Institute

of Directors in his capacity as president of the European Council.

The decision to go ahead with the visit was seen as somewhat

surprising in Belfast last night, after the UDR attack and the furious

political reaction to it. The Rev. Ian Paisley and his Democratic

Unionist Party have given notice that they are planning to protest at Mr

Haughey's presence. Last week Mr Paisley led a deputation to the

Institute of Directors in an attempt to have the invitation withdrawn.

It was being stressed last night by the organisers of Mr Haughey's

visit that he would not give a political address. He would be speaking

of the importance of the Common Market changes in 1992 for business and

industry on both sides of the Irish border.

It will be the first time in more than 20 years that Mr Haughey has

been to Belfast. The Secretary of State for Northern Ireland, Mr Peter

Brooke, yesterday backed the decision to invite him to speak. He told

reporters in Belfast that he thought the invitation to Mr Haughey was

clearly appropriate.

Mr Brooke said the question of security for Mr Haughey was a matter

for the RUC Chief Constable and the Institute of Directors. Leading

businessmen from Northern Ireland and the Irish Republic will be present

at the Europa Hotel in the heart of Belfast tomorrow morning for the

one-day conference.

Meanwhilea wave of condemnation has followed the killings.

On BBC television news Mrs Thatcher admitted she was depressed at the

reluctance of the Supreme Court in Dublin to extradite people suspected

of involvement in common criminal attacks.

''We need all the help we can get to fight people who attempt these

murders and those who succeed,'' she added. ''These people are not only

against Northern Ireland being part of the United Kingdom, they are

against democracy itself. It is in the interests of everyone south of

the border to fight the terrorism as hard as we do.''

A wave of outrage followed the killings. Mrs Thatcher, speaking on BBC

Radio Four, said: ''You take these murders of these four people today

alongside those decisions in the Supreme Court of the Republic not to

extradite those accused of violent crime - and one is very, very

depressed.''