ARMAGH, Northern Ireland (AP) _ Ireland's Cardinal Tomas O Fiaich was laid to rest today at a funeral that saw British and Irish officials seated alongside their avowed enemies in the Irish republican movement.

O Fiaich, spiritual leader of the Roman Catholics of Ireland and Northern Ireland, died a week ago at age 66 after suffering a heart attack while on pilgrimage to the shrine of Lourdes in France.

Prominent figures from around the world were among the mourners who packed the 1,500-seat St. Patrick's Cathedral in Armagh, O Fiaich's headquarters as Roman Catholic primate of All Ireland.

Attending the requiem Mass were Charles Haughey, prime minister of the Irish Republic, and Peter Brooke, Britain's chief minister in its province of Northern Ireland.

They sat a few yards from Gerry Adams and Martin McGuinness, leaders of Sinn Fein, the legal political wing of the Irish Republican Army which is outlawed in both Ireland and Britain.

The IRA is fighting to rid Northern Ireland of British rule and unite the Protestant-dominated province with the mainly Catholic Irish Republic. But at today's service, the emphasis was on O Fiaich's efforts to reconcile feuding Catholics and Protestants.

Bishop Cahal Daly reminded the mourners of O Fiaich's frequent denunciations of the IRA's campaign of violence.

''May those committed to violence listen at last in death to this plea from the heart of that good Irishman who was Cardinal Tomas O Fiaich,'' he said.

''He will be remembered as a people's prelate, a man with the common touch, a happy man who spread happiness around him; a warmhearted man whose love was without frontiers and who was greatly loved,'' Daly said.

Thousands of mourners listened to the Mass on loudspeakers outside the church. It was broadcast live throughout Northern Ireland and the Irish Republic.

Among the mourners were New York's Cardinal John O'Connor, Cardinal Bernard Law of Boston and Cardinal Francis Arinze, president of the Vatican's council for inter-religious dialogue. Two other cardinals, 50 archbishops and abbots from Irish monasteries also attended, along with Patrick Hillery, the Irish state president.

Security in and around the cathedral was tight, with dozens of armed detectives keeping watch in bulletproof cars.