At a glance, the scene early last week in the predominantly Protestant town of Portadown, Northern Ireland, seemed to have the restful innocence of a country fair. The meadows surrounding Drumcree church, 40 km southwest of Belfast, were dotted with people, tents and a capacious marquee. Flags fluttered, families picnicked, penny whistles trilled. But the bristling defenses deployed on the slopes opposite the church were anything but bucolic. Rows of razor wire cut off all links between the church grounds and the main road into town. Behind this barrier was a second: a steel wall of armored Land Rovers, parked nose to tail. And behind the second cordon was a third: a phalanx of policemen from the Royal Ulster Constabulary in full riot gear. Northern Ireland's peace, a fragile thing in the best of times, looked as gossamer as a midsummer morning mist.

By week's end that peace had evaporated as the province looked back on its worst outbreak of violence since the cease-fire called by the Irish Republican Army and the Unionist paramilitaries in August of 1994. An RUC decision to cancel a traditional Protestant march sparked three days of rioting as Unionists across Northern Ireland protested the perceived insult to their heritage. When the march was abruptly reinstated, the Catholics exploded in anger. By Friday the tourists who were boosting the region's economy had fled, arson fires were burning, hundreds were injured, and the politicians were wondering how to get peace negotiations back on track. The Social Democratic and Labour Party announced that it would withdraw from the Northern Ireland Forum talks, leaving the organization without a party representing Catholic opinion. What was all too clear was the sense that regardless of tentative political progress in recent months, Ireland's warring communities remain locked in their bitter sectarian feud. "There is still such hatred," lamented Paul Bew of Queen's University in Belfast, "hatred you could cut with a knife."

In Ulster the second week of July is the culmination of the "marching season," a time when Protestants belonging to the Order of Orange don bowler hats and orange sashes and embark on a series of marches to commemorate the Battle of the Boyne on July 12, 1690, the most important date on the Unionist calendar. On this date, William of Orange vanquished his Catholic rival, King James II, in a victory that established England's Protestant ascendancy in Ireland--an ascendancy that, in Northern Ireland at least, is celebrated by Orangemen and resented by Catholics to this day.

It was in memory of this event that 1,300 Orangemen gathered early last week in the fields outside Portadown, a town of 18,000 Protestants and 6,000 Catholics. Here the Orangemen had come to proclaim, as they have for the past 189 years, what the Rev. Ian Paisley, leader of the hard-line Protestants, refers to as their "Britishness." And here in Portadown their demonstrations provoked, as they invariably do, bitter recriminations from the town's Catholic minority. Drumcree church is a flash point because the Orangemen's route takes them along a stretch of Garvaghy Road, where the majority of residents are Catholic.

On July 7, in hopes of preventing riots, police ordered the march rerouted. Unionist leaders, however, decided to take a stand. They had walked this path for nearly 200 years, and they would not deviate from it by a inch. But RUC Chief Constable Sir Hugh Annesley remained firm; the march would not pass. Infuriated Unionists then rioted all over the province. Gangs blocked roads and cut off bridges, putting cars to the torch. Crowds stoned houses. So many fires raged in Belfast that the commander of the city's fire brigade called it his department's worst night since Luftwaffe bombs rained down in 1941. Said Robert Eames, the Church of Ireland's Anglican Primate: "If continued, this will push us back into a nightmare that we prayed had been left behind."

By Thursday morning the first contingent of two extra battalions of British soldiers had arrived from England. Soon there would be a total of 18,500 troops in Ulster--the highest number since 1982--but still they were stretched thin. Equally strained was Prime Minister John Major's majority in the House of Commons. Major's ability to govern hinges on the support of 13 Northern Ireland Unionists, and they were no happier with the RUC than were the rioters in the streets. Later, Whitehall vehemently denied any suggestion that political pressure was applied to the RUC from London. Nevertheless, on Thursday, Sir Hugh executed a surprise reversal. "We face a situation," he explained, "where potentially tens of thousands of Orangemen would face the police with a potential risk to life." In other words, the Portadown march was back on. Police began shoving Catholic protesters away and escorting the Orangemen down Garvaghy Road, to the beat of a single drum.

That appeased the loyalist anger, but now the nationalists' fury was unleashed: Catholics went wild, setting fires and tossing rocks and petrol bombs. On Thursday night in Londonderry, 900 of the bombs were hurled at the police. The next day, officers kept nationalist protesters at bay with a huge show of force, and most Unionist marches across the province went off smoothly. But then riots broke out again, prompting police to fire volleys of plastic bullets, the same ammunition they had been using days earlier against the Protestants. In Friday's unrest in Derry, a Catholic man died of injuries probably caused when he was accidentally struck by a British military vehicle; meanwhile, in Belfast, a police station came under gunfire, the second incident of armed sectarian attack on the police since the I.R.A. cease-fire.

The acrimony spilled over into relations between Dublin and London. On Friday, Irish Prime Minister John Bruton had a 25-minute phone conversation with Major. In a bbc interview, Bruton said he told Major that Britain had failed to meet the people's expectation that it be impartial and immune to pressure. Northern Ireland Secretary Sir Patrick Mayhew denounced Bruton's "extraordinary outburst."

Many Irish were fearful that the rioting would trigger reprisals from the I.R.A. For their part, loyalists complained bitterly that London, pushed by Dublin and Washington, has been making one concession after another to the I.R.A. and its political arm, Sinn Fein. Unionists are also worried that Britain is eager to get rid of Ulster altogether. But while this fear may spell more trouble for the peace talks, most Irish politicians declared that the negotiations, due to resume this week, have built up too much political and economic momentum to stall now. Still, doubts remain. The most ominous of them was sounded by Sinn Fein leader Gerry Adams. "The peace process," he declared, "is in absolute ruins."

--Reported by Helen Gibson/Belfast