BELFAST, Northern Ireland – Protestant and Catholic leaders, old enemies who until recently barely spoke to each other, took oaths of office in a power-sharing government in Northern Ireland on Tuesday, a key step in bringing a final end to sectarian violence that has killed 3,600 people in the British province.

The Rev. Ian Paisley, 81, the Protestant leader who once called Pope John Paul II “the anti-Christ,” smiled broadly inside the Stormont parliament building as he was elected to the top post in a government in which he and Catholic leaders will work together on issues from potholes to tourism. Paisley stood shoulder-to-shoulder with his new deputy, Martin McGuinness, 56, a leading Catholic politician and former Irish Republican Army commander; until recently, Paisley referred to McGuinness as a terrorist.

“I have sensed a great sigh of relief amongst all our people who want the hostility to be replaced with neighborliness,” Paisley declared Tuesday.

McGuinness said the formation of the government had “astounded the skeptics.” He gestured to his new partner, Paisley. “I want to wish you the best as we step forward into the greatest and most exciting challenge of our lives,” he said.

The grand Belfast parliament building, for years a symbol of the Troubles as it stood dormant, was abuzz with politicians, dignitaries, a heavy police presence and a throng of reporters broadcasting the proceedings live in Britain and Ireland.

The reconciliation, a primary goal of the 1998 Good Friday peace accord, drew leaders from Britain, Ireland and the United States to Belfast on a damp spring day. Quoting poets and Scripture, one leader after another spoke of the sadness of so many lives lost and the achievement of burying hatred.

British Prime Minister Tony Blair called the power-sharing government a “chance, at last, to escape the heavy chains of history.” Irish Prime Minister Bertie Ahern said that “we cannot undo our sad and turbulent past,” but “let us all resolve that this should be the last generation on these islands to feel the anger of old quarrels.”

Sen. Edward Kennedy, D-Mass., part of a U.S. delegation that came at the request of President Bush, said Northern Ireland stands as an example for the world on how to “put aside the bomb and bullet.”

It did not happen easily. The initial Northern Ireland Assembly following the Good Friday accord collapsed in 2002 amid sectarian bickering and allegations of spying by the Irish Republican Army. Since then, the province of 1.7 million people has been under the direct rule of London.

But now, elected Catholics and Protestants have agreed to sit together in the wood-paneled legislative chamber, instead of railing against each other in the streets, and to debate and vote on everyday issues, from how much each household will pay for water to which elementary schools must close.

All eyes have been on Paisley, whose support was vital as the leader of the largest Protestant party, the Democratic Unionists. Until recently, he vowed never to deal with Sinn Fein, the largest Catholic party and political affiliate of the Irish Republican Army. Paisley has softened his approach since the IRA’s 2005 disarmament and Sinn Fein’s agreement this year to cooperate with the Northern Ireland police.

A multibillion-dollar “peace dividend” from London’s treasury has also helped entice leaders to share power. As the peace process has evolved, Belfast has been transformed from an unsettled city of British army checkpoints to an emerging tourist destination.