BELFAST, Northern Ireland - The organist at St. Mathews Catholic Church was playing the hymn "Ave Maria," as Leo O'Neill recalls it, but he is not absolutely certain he remembers correctly because that June day was so sad. He and his three brothers each had a corner of their mother's casket resting on their shoulders and were carrying her up the three steps into the church, past her 22 grandchildren and dozens of friends.

That is when the trouble started. Bricks started flying over the "peace fence" erected by authorities to separate Catholics and Protestants in his tiny neighborhood in East Belfast. Then came the paint bullets, and then a couple of explosions sounded. The funeral of a 54-year-old woman who died of cancer this summer was under attack.

This is peace these days in small sections of Northern Ireland, where that word - peace - should not be taken literally but as a relative concept.

"Everybody ran into the church and closed the door, and you could hear everything outside, things hitting the doors," says O'Neill, a 30-year-old painter. "It was pandemonium. You wonder, is this really peace?"

Fortunately, or not, it is peace compared with recent years, when bombs were exploding and "murder campaigns" targeted nobody in particular, just Catholics and Protestants in general. But even through such horrible incidents as the attack on the funeral of Leo O'Neill's mother, Jean O'Neill, the relative peace has held.

Central Belfast has been all but immune to sectarian violence. Heavily bombed during World War II, it is a gray city of dismal architecture, but it has a shopping district crammed with people and a nightlife that hops well into the morning. The city is very much alive.

And, the people here seem to realize, that makes them lucky compared with the Middle East, Palestinians and Israelis, compared with the victims of Chechen rebels in Moscow and Chechen victims of the Russian military, lucky compared with children in Afghanistan whose schools are being attacked right under the rifles of an international military force.

Nobody seems to be able to figure out what to do in those places. That is partly because of the complexities of history and mostly because of the intensity of the hatred, passed down like a dominant gene to younger generations.

Northern Ireland was thought to be that way, too, a land occupied by people with insurmountable differences. But if anything positive can be taken from an attack on a funeral, it is this: The incident did not escalate. The peace, tentative as it is, was not broken.

Northern Ireland, sometimes referred to as Ulster, offers no template for solving the world's remaining conflicts, only lessons on how it has obtained its relative peace and warnings about how it might lose it.

Agreement at risk

The document that is supposed to ensure the peace is the Good Friday Agreement, signed that day in 1998. Never since its creation has it been in such danger as in recent weeks. Catholics and Protestants have been engaged in small-scale - but persistent and violent - clashes in several regions of Northern Ireland, with dozens of people injured by pipe bombs and fires and flying objects.

And the Irish Republican Army, whose terrorism is both credited and blamed for pushing the sides to agreement, has been accused of spying on its Protestant enemies in government. That led, last month, to the British government's resuming political control over the area, suspending the power-sharing executive of Protestants and Catholics. Otherwise, hard-line Protestants would have walked out, damaging the peace process even more severely.

"When I announced the Good Friday Agreement, I said that the agreement by itself did not guarantee peace and stability, that there would be difficult decisions ahead," said George J. Mitchell, the former U.S. senator who brokered the deal. "It's bumpier than I thought it would be. It's taking longer than I thought."

Whatever common elements there might be, whatever might be learned from Northern Ireland, the most important lesson here is not that reaching a peace agreement between such bitter enemies is difficult. That was known. The lesson here is that maintaining the peace might be even more difficult.

"I'm afraid. Of course, I am," confesses Leo O'Neill. "This place could still explode at any time."

There are plenty of reasons he thinks that, aside from the incident at the church. There is, for example, the incident earlier this month, when a young Catholic man was hanged on wooden posts with nails through his hands.

The Short Strand neighborhood of East Belfast is where Jean O'Neill's funeral was held. The Strand, as it is known, is a square-mile island of 3,000 Catholics surrounded by a sea of 90,000 Protestants. By most accounts, it has been the scene of the most persistent violence in Northern Ireland since the agreement was reached, and the problems in the neighborhood illustrate how the obstacles to relative peace were overcome and why the agreement thought to secure it seems so threatened.

In Northern Ireland, as in trouble spots elsewhere, the conflicts began centuries ago. The political situation has grown increasingly complex, most notably in the number of splinter groups spawned. No longer are there just two sides to the conflict, the Catholics, who historically have referred to themselves as Republicans or Nationalists, and the Protestants, who have called themselves Unionists or Loyalists.

The history of Northern Ireland is traceable to the 17th century, when English and Scottish Protestants colonized after the English military crushed rebellions, mostly led by Catholics. Had Northern Ireland united with the south, it would have been dominated by Catholics, which Irish Protestants in the north feared and fought. Most Irish Catholics, on the other hand, wanted a complete break from Britain.

It is primarily that disagreement that gave rise to the guerrilla warfare that has erupted intermittently between the two sides since then. Each time the prospect for peace has come tantalizingly close, groups opposing one agreement or another have split, giving rise to fighting within the groups.

The most serious violence in Northern Ireland these days, in fact, is Protestant paramilitary groups opposed to the Good Friday Agreement attacking other Protestants who favor it. Beatings of Protestants by paramilitaries of their own faith have become common occurrences.

"In our case, the problem with sustaining peace over the years is that no agreement has stuck because there hasn't been an agreement reached that both sides could support," said Peter Weir, a Protestant assemblyman opposed to the Good Friday Agreement.

Unraveling into violence

A treaty in 1921, which created what is now the Republic of Ireland, held until 1968, but that, too, unraveled into the type of explosion that Leo O'Neill and the other residents of Short Strand fear.

Discrimination against Catholics led to a Catholic civil rights movement that in turn led to fears among blue-collar Protestants that they would lose jobs, and that led to violence. It is no coincidence that most of the remaining violence is centered in economically distressed areas like the Short Strand, where Catholics can more ably compete for blue-collar jobs.

In the 1960s, when deadly riots broke out in Derry (or Londonderry) and in Belfast, British troops were brought in to stop the fighting, and the IRA and Protestant military groups cranked up the terrorism. More than 3,000 people have died in fighting since then in what, with rare understatement, people here refer to as "the troubles."

The Good Friday Agreement has put an end to the killing. In a referendum, Northern Ireland voters approved it with about 70 percent of the vote. But exit polling showed that while about 95 percent of Catholics voted in favor of it, slightly less than half of Protestants approved.

Residents of the Strand assert that Protestants who are against the agreement have been responsible for a series of attacks on them that have not ceased since May.

"We're 3,000 people here surrounded by 90,000," said Pat Fitzsimons, 42, whose arm was recently broken during one of the attacks. "We're supposed to be so stupid that we're creating trouble? I don't think so, mister."

Once a housing project, the Strand is a series of tightly packed and connected houses. Many of them have protective plywood or metal grating over the windows that face the peace wall - a fence 20 feet high. There is a convenience store but no real market, and residents have been prevented from going to the closest pharmacy because it is outside their gates, in Protestant territory. Murals saluting the dead remain on walls throughout the neighborhood.

In June, with objects flying from both sides of the wall - each side claims it was defending itself - five people on the Protestant side of the fence were shot.

"I'm afraid if one of those five people had been killed, you would have seen a complete breakdown," said Paul Bew, a professor at Queen's University and a friend of Unionist leader David Trimble. "I don't think anybody thought the violence was going to just disappear, but the level of it is depressing."

Perversely enough, what gives Trimble and others hope is the aftermath of incidents like Jean O'Neill's funeral and the reaction of people when Harry McCartan was found nailed to the posts.

McCartan, a Catholic, was found bloodied and unconscious Nov. 2 with rusty six-inch nails pounded through his hands and into the wood in an isolated field in back of a Protestant housing project.

Why he was attacked is in debate and being investigated. He says he was merely Catholic and in the wrong place, attacked by a Protestant paramilitary faction opposed to the peace process. Protestants say that religion and sectarianism played no part in his fate, that he was being punished for crimes.

He had been attacked before, they point out - his ankles were shattered - by other Catholics, including IRA members who went after him for not paying "protection" money.

The beating was savage. His face was so bruised and swollen that his father could identify him only through a tattoo on his arm. Newspapers and television stations in Northern Ireland showed his picture.

And, to the surprise of a lot of people in Northern Ireland, the reaction didn't even come close to setting off more violence.

"There would have been no sorting out incidents in the past," said Bew, the Queens professor. "Any bad incident of any kind of high profile would have led to serious problems."

Mitchell said that since brokering the Good Friday Agreement, he has been discouraged but remains optimistic, mostly because the relative peace has held long enough that most people in Northern Ireland are unwilling to allow any group to take them back to the bad old days.

Lesson for the world

The rest of the world can learn from Northern Ireland despite the current violence, Mitchell said. There was a persistence in the negotiating that has not been employed by groups fighting elsewhere. Among other problems, peace talks have been dropped too readily every time a cease-fire is broken - effectively handing control of the agenda to those who would continue to use violence.

Bringing entire communities into the peace process, through hearings and referendums, makes agreements more likely to win popular support, Mitchell said, which translates to less support for paramilitary or terrorist groups.

"The bottom line, and the most heartening part of the current situation, is there does not appear to be widespread conflict on either side," Mitchell said. "It's a much more open place than it was during the conflict."

Leo O'Neill is not so sure Northern Ireland is any better off than it was in 1998. His 9-year-old daughter, Leamme, was at the funeral when it was attacked. For three nights, she would not go to bed unless someone sat in her room until she fell asleep.

Her father wants to believe that there is "relative peace," but, at 30 years old, he said peace in any form is something new to him. Maybe that is why he does not recognize it. Maybe by the time his daughter reaches his age, he said, things will have improved enough that the peace is more apparent.

"I'd like it to be a hell of a lot sooner," he said, and, for the fourth time in a single conversation, he asks, "Is this really peace?"