BELFAST, Northern Ireland – A militant Free Presbyterian preacher and a former leader of the Irish Republican Army were sworn in as the joint heads of a new government in Northern Ireland on Tuesday in a move to conclude more than 30 years of conflict between Protestants loyal to Britain and Catholics who fought for a united Ireland.

The two still-suspicious new government leaders did not single out each other in the giddy handshakes shared among the new Northern Irish officials. But as the Rev. Ian Paisley of the Democratic Unionist Party and Martin McGuinness of Sinn Fein took their oaths, both sides hailed the day as the final end of the Troubles that took more than 3,500 lives between 1969 and 2001. In taking office, the two swore to oppose discrimination, promote connections with Britain and Ireland and uphold the work of the police.

The event marked a crowning achievement for British Prime Minister Tony Blair, who has spent 10 mostly frustrating years of his premiership pushing the parties toward peace. He is expected to announce his resignation this week having brought the conflict’s most intractable activists into a common government.

“Northern Ireland was synonymous with conflict. People felt that it could not be done, indeed sometimes even that it shouldn’t be done, that the compromises involved were too ugly,” Blair said. “Yet in the end it was done. And this holds a lesson for conflict everywhere.”

Paisley, the 81-year-old Protestant leader of Northern Ireland’s pro-British hard liners, for years was known as “Dr. No” for his opposition to making peace with Catholic republicans who favor leaving Britain and joining the Irish Republic. His most famous words are his declaration of “never, never, never” in response to the agreement in 1985 between Britain and Ireland that set the course for self-determination and gave Ireland an advisory role in Northern Ireland.

He recalled that he was detained temporarily by civilian authorities on the night in 1998 when the peace process here took one of its first major steps forward with the Good Friday agreement.

“If anyone had told me that I would be standing here today to take this office, I would have been totally unbelieving. I am here by the vote of the majority of the electorate of our beloved province,” he said.

“In politics, as in life, it is a truism that no one can ever have 100 percent of what they desire. They must make a verdict when they believe they have achieved enough to move things forward. Unlike at any other time I believe we are now able to make progress.”

In the final rounds of negotiations leading up to Tuesday’s ceremony, Paisley won what he viewed as his most important concession – McGuinness’ oath to support the police and urge his community to support them as well. For years, many of the province’s Catholics saw the police as parties to the conflict.

McGuinness served six months in prison in the Republic of Ireland for possession of explosives and ammunition and later was banned from entering Great Britain under terrorism laws.

Sinn Fein, the political arm of the now-disbanded IRA, is increasingly turning its attention to elections in the Republic of Ireland, which covers the southern four-fifths of the island, as a step toward winning its goal of a united territory. Thus, Sinn Fein leader Gerry Adams nominated McGuinness, his deputy, as deputy first minister in the new government.

“The road we are embarking on will have many twists and turns,” McGuinness said. “It is, however, a road which we have chosen and which is supported by the vast majority of our people. In the recent elections, they voted for a new political era based on peace and reconciliation.”

The Good Friday agreement, whose parties were pushed to a settlement by U.S. Sen. George Mitchell, D-Maine, under the Clinton administration, set the course for self-determination and gave Ireland an advisory role in Northern Ireland. The agreement led to a change in the constitution of Ireland removing that nation’s claim to the territory and created a new Northern Ireland Assembly. Both sides renounced violence as a means of settling the conflict.

The moderate Protestant and Catholic leaders who helped negotiate the agreement won the Nobel Peace Prize in 1998. But the two, David Trimble, then head of the Protestant Ulster Unionist Party, and John Hume, former leader of the Catholic Social Democratic and Labor Party, were beset with opposition from radicals within their own movements. In the end, it took the naysayers, Paisley and Adams, to negotiate what looks to be a durable peace.

Under the agreement, Northern Ireland remains part of Britain unless – Sinn Fein would say until – a majority in the province vote to leave Britain and join Ireland. But Ireland and Britain have a role in the province through separate north-south and east-west councils.

“I have no doubt that we’re now in a situation of lasting peace,” Hume said after the ceremonies, during which Blair and Irish Prime Minister Bertie Ahern watched with other dignitaries from a public viewing gallery. “I think it’s a very moving day for all of us in Northern Ireland, given what the people of Northern Ireland have suffered during the last 30 years.”

The two sides are working in unison already to persuade British finance minister Gordon Brown to expand the $70 million “peace dividend” Britain is extending to Northern Ireland to get the new government off the ground. But they will almost certainly clash soon on issues such as performance testing in the schools – an issue both pledged to work on through normal channels of government.

The violence in Northern Ireland erupted in 1969 with civil rights marches launched by mainly Catholic nationalists, who were reacting to perceived discrimination in elections, jobs and housing and laws that allowed for the internment of citizens.

Communal conflict broke out in several parts of the province, quickly expanding to encompass the police and army, loyalist paramilitaries and the Provisional IRA, which vowed to wage armed struggle against British rule in Northern Ireland. IRA bombs planted as far away as London and Germany became a fixture of the conflict.

In the years of negotiations that followed the peak of the violence, the IRA implemented a cease-fire and gave up its weapons, winning release of prisoners who renounced violence. Last week, the Protestant Ulster Volunteer Force moved in a similar direction, announcing that recruitment, military training and targeting had ceased.

U.S. Sen. Edward M. Kennedy, D-Mass., who has long been an activist in the Northern Ireland peace process, also attended as part of a U.S. delegation.