ELFAST, Northern Ireland — Paving stones and gasoline bombs were raining in on a working-class Protestant neighborhood over the high wall separating it from a Catholic enclave. A roof caught fire, boarded-up windows clattered and shook from direct hits, and two residents, Raymond and Patsy Laverty, talked about how the Northern Ireland peace movement they once supported had sold out their people. 

"The Catholics treat us like we lived in the big house all those years, but we were never well off and we were oppressed too," Mr. Laverty, 41, said, watching a bombardment that has become almost routine. 

"We hoped for a change," said his wife, "but how can I tell my kids the peace process is working when we're getting shot at and you have to be Catholic to get a job."

Once, of course, only Protestants were welcome in the workplace in Belfast. Mrs. Laverty, 40, winced at the reminder. "I guess we've come full circle, haven't we?" she said. 

Northern Ireland's majority Protestants have, in fact, taken on the grievances of a minority, and their growing feeling of precariousness in the land they once dominated is being seen as the biggest menace facing the province's fragile peace deal. 

The 1998 agreement created equal opportunity arrangements in Northern Ireland's political, institutional and professional life to try to halt violence and start to build trust between the two rival communities. It balanced promises for Catholics — known as nationalists and republicans because of their wish to see Northern Ireland become part of the Irish Republic — with guarantees to Protestants — known as loyalists or unionists because of their desire to keep their land part of the United Kingdom.

But while Catholics have succeeded in moving into residential and job areas they never penetrated before and have felt their public influence enhanced by aggressive and fiercely focused political leadership, Protestants have despaired as their society has appeared to come apart.

Their working-class communities have descended into turf wars and gang struggles, their politicians have fallen into name-calling disputes among themselves and their educated elites have disengaged from public life, leaving the city for the security of hedged suburbs or fleeing Northern Ireland altogether. A census out later this year is expected to show the Protestant majority down to 51 percent and the Catholic minority up to 45.

"You find tremendous confidence among Catholics and an utter absence of it among unionists," said the Rev. John Dunlop, 62, of the Rosemary Presbyterian Church. 

The Northern Ireland peace accord has attracted international notice for boldly tackling a problem emblematic of modern combat — one where nations do not war with other nations, but differing cultural, religious or ethnic groups struggle for shared space within the same boundaries. 

Four years later, however, Belfast remains a city with Catholic and Protestant working-class communities demarcated by painted curbs, Irish or British flags and walls bristling with concertina wire and portraying militant murals of masked gunmen pledging the destruction of their enemies — who in Belfast are usually their neighbors. 

Cease-fires by paramilitary groups put an end to the systematic organized violence that cost 3,600 lives in the three decades before the agreement, but the conflict has moved increasingly into these so-called interface areas of Belfast where, this summer, Catholics and Protestants have plunged their streets into the worst rioting the city has seen in years. 

No one seems to have anticipated how vulnerable the Protestants would come to feel with the Catholic ascendancy, and the great frustration facing pro-agreement Protestants these days is persuading unionists of their own success.

"People have forgotten the deep sense of daily annoyance living here used to be," Dr. Dunlop said. "It was magnificent those first days just being able to drive downtown without being stopped at police checks and roadblocks all the time. The problem is that there is a tendency to get used to normality very easily." 

Chris Gibson, the head of Northern Ireland's biggest business group, looked out over Belfast's harbor and marveled at the number of cranes across the horizon and the construction sites along the Langan River where Victorian courthouses and bank buildings are being restored and new office towers are going up. "There's been so much progress," he said. "But we can't convince unionists of it because they are so demoralized and so divided."

Dr. Dunlop said he despaired over a new pattern in his neighborhood where Protestants were moving out now that Catholics were moving in. "A Catholic family just down the block told me they hoped Protestants would buy the next property that came on the market. They said, `We came here to get out of a Catholic ghetto, not to create a new one.' " 

He added, "If Protestants are not happy living next to Catholics, what future do we have in this land?" 

Protestants approved the peace accord in a referendum in 1998, but everyone agrees that they would not do the same today. In what amounts to a new referendum on the matter, Ulster's voters will elect members of the Northern Ireland Assembly in May 2003, and the fear of pro-agreement politicians is that the disillusioned Protestants will desert the moderate Ulster Unionist party for the hard-liners of the Rev. Ian Paisley's Democratic Unionist Party, who are pledged to bring down the power-sharing arrangements with Catholics. 

All eyes are on David Trimble, leader of the Ulster Unionists and first minister of the Assembly. He has already had to face down a number of leadership challenges from dissidents in his own party, and he is increasingly beleaguered in his role as the most vocal and forceful Protestant advocate of the peace agreement. 

"He is in one hell of a mess," said Paul Bew, professor of Irish politics at Queen's University, who is a friend of his and an adviser to the party. "Republicans have a collective sense of purpose, while the unionists are individualistic, divided and suspicious, with no sense of communal identity." 

There have been significant changes in Protestant society that have ended up skewing support for the peace agreement. In the Northern Ireland their parents grew up in, Protestant youths had jobs waiting for them in the industries their fathers and grandfathers worked in — engineering, the shipyards, the aircraft factory, the rope works, the linen mills. So they did not pursue higher education, and the current generation suddenly finds itself underequipped for the skilled jobs in Northern Ireland's new information technology and services economy. 

"The Catholics did just the opposite," said the Rev. Gary Mason, 44, head of a Methodist mission in an area of Protestant East Belfast under almost nightly bombardment. "They went after education, they did it here in Northern Ireland, and they did it well." 

The majority of students at Queen's, Belfast's premier university, are now Catholic, and Ulster's businesses, operating under new affirmative action mandates, are employing them. 

The gains that unionists made in the peace agreement are substantial but less easily felt than the progress republicans made. Republicans gained long-sought political and cultural parity with unionists and they advanced the North's linkages with Dublin, feeding their dream of merger with Ireland. 

The unionists achieved official recognition that Northern Ireland would remain British as long as its residents wanted it that way, and they secured the elimination from the Irish Constitution of clauses making territorial claims on the North. But implicit in those accomplishments is the admission that the day will come when demographics will put an end to those assurances. 

Many unionists, therefore, denigrate their own gains as reversible and view republican progress as permanent. "As Ian Paisley once put it to me in an interview, unionists don't aspire to anything," said Richard English, professor of politics at Queen's. "We've got what we want, and any change means we lose out." 

Unionists put little trust in republican claims of commitment to peace or statements like Tuesday's formal apology by the I.R.A. for the deaths of civilians it caused. 

Suspiciousness and internal disputes have cut into the capacity to produce political leadership. "People here haven't stopped playing the old zero-sum game — what's your enemy's gain must be your loss," said Mr. Gibson.