Sinn Fein leader Gerry Adams led his IRA-allied party down the road from revolution to reform Sunday, winning full backing for the Northern Ireland peace accord against the odds of history.

In a fundamental reversal of decades-old policy, 331 out of 350 Sinn Fein activists voted to let their leaders participate in a new compromise administration for Northern Ireland. The verdict followed several hours of public debate at the Royal Dublin Society hall.Sinn Fein's warm, if belated, embrace of the accord won't make ratification of the deal any easier in May 22 public referendums. Although Northern Ireland's main Protestant party, the Ulster Unionists, approved it last month, many Protestants will oppose any deal deemed acceptable to Sinn Fein.

Still, the decisive outcome marked a personal triumph for Adams, who since taking charge of Sinn Fein in 1983 has inched the party slowly out of isolation while averting potentially deadly splits in the Sinn Fein-Irish Republican Army movement.

"Today we cleared the way for the future. Tomorrow we start to build the future," Adams told 1,000 cheering delegates.

Adams emphasized that the decision doesn't mean Sinn Fein accepted the right of Northern Ireland to exist, even though he is now free to help govern it.

That key issue has driven the past 30 years of bloodshed - and is spurring dissidents to try to wreck the IRA cease-fire of July 1997.

During the conference, IRA dissidents claimed responsibility for firing two mortar shells at a police barracks in the Northern Ireland border town of Belleek, injuring no one. On Saturday, in their first public statement, they called the truce "over" and accused Adams of taking Sinn Fein down the road of accepting Ireland's partition.

Because of the potential for such splits, Adams had delayed formally accepting the compromise accord reached April 10 with the British and Irish governments and seven other Northern Ireland parties.

British Prime Minister Tony Blair welcomed Sinn Fein's decision. "It means Sinn Fein has signed up to a process in which there is no place whatsoever for violence or the threat of violence," his office said in a statement.

Adams and Martin McGuinness, Sinn Fein's chief negotiator, offered polite applause to about a dozen speakers who bluntly opposed changing Sinn Fein's policy of boycotting government institutions in Northern Ireland, a Protestant-majority state founded in 1920.

"Your beliefs are born in your heart, your strategies in your head. When the two collide, something has to give," said John Murphy, a Sinn Fein activist in his mid-20s from the Irish Republic border town of Monaghan who wanted to reject the agreement.

But for most IRA supporters, the head prevailed. Sinn Fein leaders argued that Sinn Fein had to sit on the proposed 108-seat Assembly in Belfast, which would be overseen by a 12-strong Executive from several parties including Sinn Fein.

"Going into the Assembly is the right tactic at this time," said Gerry Kelly, legendary former IRA mastermind of London car bombs and prison breaks, who is now a Sinn Fein negotiator.

The delegates voted on several issues Sunday but only formally counted votes on the crucial question of whether to allow Sinn Fein to sit on the assembly. The decision to support the peace accord was reached by a near-unanimous show of hands.

Comparing the peace process to playing chess with the north's pro-British Protestant politicians, Kelly said Irish republicans shouldn't cede a single square on the board to their opponents.

He said Protestants had pushed hard in the 22 months of negotiations to create a new Northern Ireland government on the assumption that Sinn Fein would choose to boycott it.

"We need to put as many rebels as we can in amongst our opponents and to take them on in every way," Kelly said.

The British and Irish governments backed Adams' sales pitch with action.

Late Saturday, the British temporarily freed four influential IRA prisoners from Northern Ireland prisons to permit them to attend the debate.

And the Irish government surprised virtually everyone by temporarily freeing the IRA's four longest-serving prisoners to attend the conference, too.