Protestant and Catholic hard-liners scored unprecedented gains Friday in Northern Ireland's elections to the British Parliament, reflecting shifts in power that could threaten the province's 1998 peace accord.

A steep Protestant swing toward the uncompromising Democratic Unionist Party in Thursday's vote spelled trouble for efforts to keep a year-old Catholic-Protestant government running.

The power-sharing coalition joins the territory's four biggest parties, two Irish Catholic and two Protestant. The contest for Northern Ireland's 18 seats in Parliament demonstrated the tussle for dominance within each of the camps.

David Trimble's Ulster Unionist party was trying to fend off the Democratic Unionists, who oppose Trimble's compromise policies.

The Democratic Unionists won a record five seats and came close to winning others. Their leader, the Rev. Ian Paisley, vowed to force an end to a power-sharing experiment that includes the Sinn Fein party, which is allied with the Irish Republican Army.

His party cut deep into the traditional lead of the major Protestant party, the Ulster Unionists.

"David Trimble has destroyed this country with his drip-feed of concessions to the IRA," Paisley declared in his own North Antrim constituency.

Sinn Fein scored its own historic gains among the province's Catholic community. It won four seats, double its previous record.

A loss by Jim Cooper left Ulster Unionists with six seats, down from 10. Trimble, who has repeatedly survived threats to his leadership as he steered Protestants through a series of compromises with Sinn Fein, held his own parliamentary seat, but suffered sustained verbal abuse from a hostile Protestant mob at the counting center.

"We are not quitters," Trimble shouted above a din of heckling. "We will keep at this job until it is done."

In another development, Sinn Fein outpolled for the first time the province's traditional No. 1 Catholic party, the moderate Social Democratic and Labor Party, which retained its three seats. Sinn Fein received 21.7 percent of votes, the SDLP 21 percent.

Ulster Unionists did wrest back two seats previously held by Protestant hard-liners. But, emphasizing the split within his party ranks, one of Trimble's candidates spent his victory speech denouncing parts of the 1998 accord.

Elsewhere, Democratic Unionists ascended to previously unseen levels and jubilantly predicted Trimble's political demise.

One Ulster Unionist fared exceptionally well: hard-liner Jeffrey Donaldson, long considered Trimble's most likely successor as Ulster Unionist leader. He saw his vote rise slightly to nearly 26,000 in Lagan Valley.

Sinn Fein leader Gerry Adams registered a crushing 20,000-vote majority in his West Belfast constituency. The party's other incumbent, former IRA commander Martin McGuinness, scored another easy victory in his Mid-Ulster district.

Sinn Fein's surging vote demoralized the Social Democratic and Labor Party, which has traditionally won most Catholic votes with a trenchant anti-IRA stand.

The changing electoral tide proved most striking in West Tyrone, a hotly contested rural district along Northern Ireland's border with the Republic of Ireland. There Sinn Fein vice president Pat Doherty beat the SDLP's Brid Rodgers by nearly 6,000 votes.

SDLP leader John Hume, who shared the 1998 Nobel Peace Prize with Trimble, easily defended his seat in Northern Ireland's second-largest city, Londonderry.

Hume's deputy Seamus Mallon, who also holds the No. 2 post in the Northern Ireland administration, beat Sinn Fein by just 3,000 votes.

Elected Sinn Fein members planned to continue to boycott debates and votes in Parliament in London because they would be required to give an oath of allegiance to Queen Elizabeth II.