BELFAST, Northern Ireland (AP) – Northern Ireland faced a hopeful new era Tuesday as long-warring Protestant and Catholic chieftains prepared to forge a joint government designed to consign to history decades of violence that claimed 3,700 lives.

Protestant firebrand Ian Paisley and Irish Republican Army icon Martin McGuinness, who took diametrically opposed sides in a four-decade struggle over this British territory, have pledged to lead a 12-member administration, as a 9-year-old peace accord intended.

The British and Irish prime ministers, Tony Blair and Bertie Ahern, were traveling to Belfast to celebrate the moment when the Northern Ireland Assembly jointly elects Mr. Paisley, leader of the Democratic Unionist Party, and Mr. McGuinness, deputy leader of the IRA-linked Sinn Fein.

Messrs. Paisley and McGuinness, who was long committed to destroying Northern Ireland rather than governing it, are also being bound together by taking a common oath of office. It requires all government ministers “to uphold the rule of law based as it is on the fundamental principles of fairness, impartiality and democratic accountability, including support for policing and the courts.”

Northern Ireland Secretary Peter Hain, the British minister handing over control of most government departments Tuesday, said he was astonished that two men who had been “sworn and bitter enemies” had convincingly buried the hatchet in recent weeks.

“That’s what fills me with optimism as well,” Mr. Hain said. “Not just that the darkness and horror of the past is now behind us, but that there is a real prospect of this government working.”

Both Mr. Paisley, 81, and Mr. McGuinness, 56, spent time behind bars for their extremist paths and analysts agree that both, in very different ways, have blood on their hands today.

Mr. Paisley, a bombastic orator who leads his own virulently anti-Catholic church, was imprisoned in 1969 for leading an illegal demonstration against Catholic marchers demanding equal rights in voting, housing and employment. His strident, stubborn invective fanned the flames of Protestant mob violence and helped to delay by decades today’s historic compromise.

Mr. McGuinness, a high school dropout from Londonderry who rose to become the city’s IRA commander, served two short 1970s sentences for IRA membership – and spent many years more on the run while serving in the IRA’s ruling “army council,” the seven-man committee ultimately responsible for killing nearly 1,800 people and maiming thousands more.

Power-sharing was a central goal of the American-brokered Good Friday peace accord of 1998, but Blair and Ahern since have had to lead several summits aimed at coaxing local leaders of the British Protestant majority and Irish Catholic minority together.

A four-party coalition led by moderate Protestants and Catholics took power in December 1999 but repeatedly broke down amid confrontations between Protestants and Sinn Fein. It collapsed for good in October 2002 over allegations that the IRA was using Sinn Fein’s position inside government to pilfer files and other intelligence on potential targets.

Mr. McGuinness served as education minister in that coalition. Mr. Paisley, who once campaigned on a slogan of “Smash Sinn Fein,” permitted two of his deputies to take part – but not to sit in Cabinet meetings because of Mr. McGuinness’ presence.

When 2003 elections to the Northern Ireland Assembly produced twin triumphs for Mr. Paisley’s Democratic Unionists and Sinn Fein, it appeared to cripple prospects for revived power-sharing.

But prospects were been transformed by the IRA’s 2005 decisions to disarm and renounce violence, and Sinn Fein’s vote in January to open normal relations with the Northern Ireland police.

Mr. Paisley stunned Northern Ireland on March 26 by appearing live on television beside Sinn Fein leader Gerry Adams – barely an hour after the two men negotiated together for the first time – to declare a deal.

“I see today very much as fulfilling the wishes of all the people of Ireland,” Mr. McGuinness said.

But in an editorial, the Belfast Telegraph noted that to be considered successful, power-sharing must bring together the two sides of the community – which in working-class parts of Belfast is literally divided by walls of brick and steel dubbed “peace lines.”

“Political agreement is just another step on Northern Ireland’s journey from darkness to light,” the newspaper said. “Not until sectarian divisions are erased, and all the peace lines dismantled, will the new Northern Ireland be able to reach its full potential.”