TO OUTSIDERS, nothing seems more stupid than Northern Irish "Orangemen" proclaiming their Britishness by celebrating the 309-year-old victory of a Dutch king over an English monarch.

But the fact that the Dutch king, William of Orange, had a Protestant army while the defeated forces of King James II were Irish Catholics is reason enough for many of Northern Ireland's Protestants.Their Orange Order was set up 204 years ago to perpetuate the memory of the Irish defeat at the battle of the River Boyne on July 12, 1690. Every summer it marches through towns and villages in the six counties that form the British province atop the Irish Republic, bringing Catholics to a boil.

The marching season has begun again, despite a landmark deal struck in April and approved in a May referendum to end 30 years of sectarian conflict and eight centuries of Irish-British enmity. A series of parades set to culminate on Monday have already brought violence and tension to a community trying to cement the still tenuous peace and heal old war wounds.

As usual the focus is on Portadown, 35 miles from Belfast, where the Orange Order was founded in 1795 to defend the "reformed faith" against "the false doctrines of Popery." To Catholics, it is a symbol of British colonialism and a galling reminder of the discrimination they suffered not too long ago at the hands of the Protestant majority.

Orangemen, clad in their old-fashioned uniform of suits, umbrellas, bowler hats and orange sashes, have paraded past Catholic homes on the Garvaghy Road since 1807, asserting their right to "march the Queen's highway" to the Drumcree Anglican Church. Their recent marches have ended in violence three years in a row.

In 1996, police tried to block the Orangemen at Drumcree but relented after four nights of intensifying bloodshed, forcing Catholic protesters off Garvaghy Road. In 1997, British soldiers and police escorted the marching Protestants, sparking widespread Catholic rioting.

This year an independent Parades Commission banned the marchers from Portadown's Catholic quarter, triggering Protestant riots aimed at getting Britain to reverse the decision. But British Prime Minister Tony Blair refused to do so, and British troops reinforced about 2,000 policemen blocking the Protestants' path.

Protestant protesters have attacked policemen and their families in Belfast and surrounding communities, burned Catholic homes and hijacked cars. More than 500 attacks were reported in the first five days of rioting, including 14 shootings, 29 bombings, 73 homes of Catholics or police officers vandalized, 93 businesses and schools damaged by fire and more than 400 vehicles stolen and burned. At least 50 police officers were injured.

Most of the violence was blamed on the militant Ulster Defense Association, fanned by the fiery rhetoric of Protestant rabble rousers such as the Rev. Ian Paisley. And many found it ironic that the UDF was targeting the predominantly Protestant Royal Ulster Constabulary.

For years, Catholics have accused the RUC and British troops of siding with Protestant gunmen against the outlawed Irish Republican Army. The Protestants, in turn, have always maintained that the IRA's political struggle is simply a "law and order problem," and they are merely helping the police battle Catholic "terrorists."

Now the Protestants are showing quite graphically on television screens around the world that they too are a law-and-order problem - one that must be quickly suppressed if the peace agreement is to be saved.

It was approved by more than 90 percent of the province's Catholics and more than half its Protestants, suggesting that the troublemakers are a distinct minority. And, to be fair, the leaders of the Orangemen do not condone the violence.

Less than two weeks ago, Northern Ireland's first parliament in nearly a quarter of a century held its inaugural session, with once-bitter enemies sitting across the aisle from each other. David Trimble, the assembly's Protestant leader, acknowledged that "there are people in this room who have done terrible things in the past. But just because they have a past doesn't mean they cannot have a future."

Now the past intrudes again, and the future could be lost for a road.